Utilizing the characteristic properties of tin(II) species, various types of new synthetic reactions are developed and the results are summarized in this article.
It was found that tin(II) enolates are readily generated on treatment of carbonyl campounds with tin(II) triflate and N-ethylpiperidine, which in turn react smoothly with aldehydes to afford aldol products in highly stereoselective manner. In comparison with lithium and boron enolates, tin(II) enolates display enhanced reactivity towards ketones, and a facile method for the directed aldol reaction between two different ketones in realized.
he generation of tin(II) enolates from 3-acyl-2-thiazolidinethiones als o proceeds successfully on treatment with tin(II) triflate and N-ethylpiperidine, and the resulting aldol products are readily converted to various β-hydroxy carboxylic acid derivatives and β-hydroxy aldehydes. This reaction is further aβlied to the stereoselective construction of carbapenem skeleton, and the intermediate of thienamycin synthesis is synthesized with high stereoselectivity.
Utilizing the specific affinity of fin(II) with sulfur, a novel catalytic metal enolate mediated aldol reaction is realized. Thus, just by the action of a catalytic amount of fin(II)triflate salt of ethanethiol, the mixture of α, β-unsaturated ketone, aldehyde, and trimethylsilylether of ethanethiol affords the aldol type product in good yield.
The Michael addition reaction of metal enolate to α, β-unsatura ted ketone still remains as one of difficult problems due to the difficulty in controlling 1, 2- and 1, 4-addition. Really, tin(II)enolate alone did not add to α, β-unsaturated ketone efficiently. However, when trimethylsilyl chloride is added as an activator of the ketone, the Michael reaction proceeds smoothly to give the corresponding product in good yield.
When p-benzoquinone is employed as an acceptor, a novel aldol-reduction reaction proceeds when silyl chloride is added as an activator. According to this procedure, α-aryl carbonyl compound is easily prepared from the corresponding carbonyl compound and quinone.
Finally, a mild and efficient catalyst system is developed by the combined u se of trimethylsilyl chloride and fin(II) chloride. Various reactions of silyl enol ether with aldehydes, acetals, and α, β-unsaturated ketones are effectively catalyzed by the combined use of mild Lewis acid (tin(II) chloride) and neutral molecule(trimethylsilyl chloride).

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A bulky group can protect a reaction center of the generally unstable chemical species from the oligomerization of the species because of the large steric hindrance. This method'is very suitable to determine the physical properties without a perturbation from any electronic effect. In this review paper, using very bulky groups such as 2, 4, 6-tri-t-butOphenyl group (thereafter abbreviated as Ar) as sterically protecting group, symmetric and unsymm etric diphosphenes (ArP. PAr'), the corresponding oxide (ArP=P(0)Ar) and sulfides (ArP=P(S)Ar'), diphosphane (ArPH-PHAr), phosphaethylenes (ArP=CRR'), dithioxophosphorane (ArPS₂), iminomethylenephosphine (ArP=C=N-Ph), 1-phospha- (ArP=C=CPh₂), and 1, 3 diphosphaallenes (ArP=C=PAr) were isolated as stable compounds and characterized.
Addition of halogens, oxidation, sulfurization, selenization, reducti on, nucleophilic additions of hydride 'ion and butyllithium, and formation of VIB metal carbonyl complexes for diphosphenes, and photoisomerization, sulfurization, reduction, and formation of VIB metal carbonyl complexes for phosphaethylenes, 1-phospha-, and 1, 3-diphosphaallenes were investi gated. In some cases, the structures and stabilities of the simplest model compounds were calculated using ab initio MO method and compared with the observed results.

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Monosulfoxide of 1, 5-dithiacyclooctane was dissolved in conc. H₄SO₄ to be converted to the 1, 5-dithiodication ( 1 ) which was idntified by ¹H- and ¹³C-NMR. The dication ( 1 ) was isolated as a hygroscopic powder-like salt by quenching the H₂SO₄ solution with anhydrous ether. The dication ( 1 ) was further converted to the corresponding trifluoromethanesulfonates as a stable crystalline compound. Similarly, other monosulfoxides of various cyclic and acyclic 1, n-dithia derivatives were treated in conc. H₂SO₄ to give 1, n-dithiodications. These monosulfoxides underwent the Pummerer rearrangement upon treatm ent with Ac₂O giving both α- and ω-acetoxy-1, n-dithioethers. Formation of 1, n-dithiodications was also observed during the reactions.
New metacyclophanes(2, 11-dithia[3.3]metacyclophane) bearing a bridged sulfur atom between 9 and 18 positions in the rings were prepared. Both monosulfoxides or the cyclophane itself' gave a new trithiodication where the charges are delocalized among three sul fur atoms with the central one taking a hypervalent structure.

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Three types of the typical reaction and character of hypervalent sulfuranes are described mainly based on the results of the author's research group. First, it is presented that several types of iminothiadiazolines behaved as masked 1, 3-dipoles to react with activated acetylenes and imidates (nitriles) in the fashion of addition-elimination and addition-ring-transformation respectively, where the corresponding thiathiophthene analogous sulfuranes (10-S-3)were invoked as the intermediates. Second, ring-transformation (bond switch) equilibrations were observed for 5-(2-aminovinyl)isothiazole system in neutral solutions and also for 5-(aminomethyleneamino)1, 2, 4-thiadiazole system in acidic solutions. The rates were determined as the following, is e., for the former([28d]):_??_=6.21×10^-6s^-1, ΔH=12.2 k cal/mol, ΔS=41e. u.; for the latter ([26-H⁺]):_??_=10^6.4s^-1. Third, the formation of 10-S-4 sulfuranes were exemplified by the single crystal X-ray analysis for dibenzothiazocinium systems due to the 1, 5-transannular interaction between the sulfonio and the amino groups. The S-N bond lengths of the sulfuranes decrease and the sulfur atom gradually attains better TBP configuration according to the increase of electronegativity of the substituents at the sulfur. It is also shown that the electronic effect of the substituent at the sulfur was transmitted to the amino group through bond and/or through space by ¹H-and ¹³C-NMR measurements.

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Some new aspects of multiple-bond organic compounds-containing sulfur and slenium atoms have been described with emphasis on the author's recent work. The relative stability and geometries of various isomers of HNS2 have been calculated by ab initio method, the most stable one being (Z)-HN=S=S, consistent with the experimental fact that Ar'-N=S=S (Ar'=2, 4-di-t-butyl-6-methylphenyl) exists as Z-form as determined by X-ray crystallographic analysis. The first isolable aromatic (ArCHS, 4, 6-tri-t-butylphenyl) and aliphatic thioaldehyde (TsiCHS, Tsi=tris(trimethylsilyl) methyl) have been synthesized and some reactions of these thioaldehydes including thermolysis, photolysis, and reactions with organometallics have been carried out. Some attempts of the synthesis of stable aromatic and aliphatic selenoaldehydes have been made and ArCHSe (Ar=2, 4, 6-tri-t-butylphenyl) has been found to be much more reactive than the corresponding thioaldehyde, ArCHS, undergoing isomerization into a tetrahydro-2 H-2-benzoselenin derivative even at room temperature.

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Development of facile synthetic methods of sodium or lithium salts of hydrogen tellu. ride and tellurols opened up a new field of tellurium chemistry, where these tellurium compounds have been used as the reducing agents. On the other hand little attention has been paid to the reactivity of hydrogen telluride itself. Since hydrogen telluride has relatively weak Te-H bonds (bond energy=64 kcal/mol), it was expected that hydrogen telluride should have a high potentiality as a reducing agent.
We examined the reactivity of hydro gen telluride generated in situ by the hydrolysis of aluminum telluride and found that hydrogen telluride had a unique reducing ability toward some specific functional groups containing nitrogen and/or oxygen atoms. For example, azo-, azoxy-, and nitrosobenzene were reduced to hydrazobenzene under mild conditions. Nitrobenzenes, phenylhydroxylamine, imines, and enamines gave corresponding amines. Aromatic aldehydes were reduced to alcohols at 0°C in quantitative yields. Reduction of aliphatic aldehydes was slow under the identical conditions. Selective reduction of C-C double bond of α, β-unsaturated carbonyl compounds was achieved at lower temperatures. As an application of this reduction system, a new convenient method for reductive alkylation of amines with carbonyl compounds by use of aluminum telluride and water has been developed. When the reaction of aliphatic aldehydes with hydrogen telluride was carried out under acidic conditions, the reduction to alcohols was suppressed resulting in the formation of dialkyl ditellurides.
Present reduction method is quite simple in the experimental procedure, so that it will be useful in organic syntheses. Especially, the applicability of D₂O as the deuterium source in the present reaction is of vital importance as demonstrated in the reduction of aldehydes.

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So far, studies on mass spectrometric fragmentation processes of organogermanium cornpounds have been reported mostly for acyclic systems. In this paper, we report the mass spectrometric fragmentations caused by electron impact and their analysis for 1, 1-dimethylgermacyclohexane(1 ) and related compounds.
The main path of fragmentation of 1 is a loss of an ethylene moiety from the molecular ion, and a subsequent loss of a cyclopropane moiety to yield a dimethylgermyl cation radical. A loss of a methyl radical from the dimethylgermyl cation radical yielded methylgermyl cation which forms the base peak (m/z 89 for the hydrogen compound or m/z 92 for the deuterium compound). A further loss of a methyl moiety yielded a germanium ion. It was found that the main pathway is accompanied by other minor pathways.
The proposed pathway was confirmed by the shift method, i. e., a comparison of fragmentation pattern between the parent and appropriately substituted species. In this study, 1, 1, 3and 1, 1, 4-trimethylgermacyclohexanes(3 and 5) and 1, 1-bis(trideuteriomethyl)derivatives of 3 and 5 were analyzed.
For all of th e compounds investigated the base peak ions are identical, and ions which contain a germanium atom are more abundant than those without.

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Alternate-condensation rections of thermally evaporated germanium vapor with polyhaloalkanes were investigated. Germanium atoms were inserted into C-Cl and C-Br bonds, but not into C-H, C-F, and C-C bonds. The reactivity of germanium atoms toward polyhaloalkanes was discussed.

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Primary processes on photolysis of group 4B compounds containing carbon-germanium and carbon-tin bonds were studied at room temperature. The germyl and stannyl radica ls generated were observed directly by laser photolysis. Laser photolysis study of phenylsubstituted germanium compounds suggests that the corresponding germyl radicals are formed from their triplet states.

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Treatment of the chiral steroidal acetal ([8], S-R, R isomer), prepared from the steroidal aldehyde [3] and (2 R, 4 R)-(-)-2, 4-pentanediol, with allyltrimethylsilane [12 a], 9-ally19-BBN [12 b], or allyltributylstannane [12 c] in the presence of TiC14 followed by the usual work-up gave the homoallyl alcohol ([14], S, S-isomer) either exclusively or highly predominantly. Although the corresponding reaction of the chiral acetal ([9], S-S, S isomer), prepared from [3] and (2 S, 4 S)-(+)-2, 4-pentanediol, with [12 a] or [12 b] gave again [14]predominantly, an isomeric homoallyl alcohol [16], 5, R-isomer, was obtained preferentially with [12 c]. Similarly, the reaction of stannylacetylenes ([11 a], [11 b]) with [ 8 ] produced the S, S-isomer [13], while an analogous reaction with [9] gave the S, R-isomer [15] predominantly. The reaction of [9]with [11 c] gave the S, S-isomer [13] with high stereoselectivity. These results clearly indicate that the enantiomer excess or even the direction of asymmetric induction strongly depends on the nucleophilicity of organometallic compounds, and provide for the first time evidence that the bond-formation and bond-cleavage are fully concerted to achieve the high asymmetric induction dictated by acetal templates.

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Irradiation of an aqueous acetonitrile solution containing 1, 1-dicyano-2-(2-furyl)ethene and allyltributylstannane in the presence of phenanthrene gave regioselectively 5, 5-dicyano-4-(2 fury1)-1-pentene. Similar photoaddition reactions occurred upon irradiation of mixtures of 2-(2-furyl- or 2-thienyl)-substituted 1, 1-dicyanoethene derivatives and allylic and benzyli c stannanes in the presence of phenanthrene, affording the corresponding allylated or benzylated products in good yields. In these photoreactions, the allylic or benzylic groups were introduced into the β-carbon and hydrogen into the α-carbon to the cyano function of 1, 1-dicyanoethene derivatives with high regioselectivity. Such photoallylation reactions did not occur when allylic silanes were used in place of allylic stannanes. No reaction took place by irradiation in nonpolar solvents and also by refluxing the reaction mixture in the dark. The electron transfer mechanism is proposed for the photoreactions. The reactions involve coupling between 1, 1-dicyanoethene radical anions and allylic or benzylic radicals which are produced from the stannane radical cations.

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Catalytic capability of complexes between Bu₃SnI or Bu₂SnI₂ and some ligands such as Ph₃P, Ph₃P=O, Bu₄PI, and Ph₄SbI was examined for the cycloaddition of carbon dioxide to oxiranes. Some complexes showed quite high activity, though the individual component of the complexes did not individually. The combination between tin compounds and ligands was essential. For example, Bu₃SnI-Ph₃P showed quite low activity in contrast to the active Bu₂SnI-Ph₃P complex. Catalytic activity depended strongly on the stability and structure of complexes. In addition, the activities of these complexes were compared with those in the polymerization of trimethylene carbonate. It was revealed that the Lewis acidity of organotin halides was weakened by the complexations, because the polymerization using the complexes, Bu₃SnI-Bu₄PI [E] and Bu₃SnI-Ph₄SbI [G] was remarkably suppressed.
Consequently, both complex [E] and [G] were excellent catalysts, cle arly producing several kinds of carbonates under mild conditions as shown in Table 4.

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The reduction of various 1-phenyl-2(1H)-pyrimidinethiones substituted on the ortho and para position of the N-phenyl group by hydroxyl, methoxyl, or methyl group with metal hydride complexes (lithium aluminum hydride, lithium borohydride, or sodium borohydride)was investigated. It was found that the ratio of dihydropyrimidines to tetrahydropyrimidines depended largely upon the phenyl substituents and the metal hydride complex used. The influence of the ortho and para substituents was not observed when sodium borohydride was used. However, when lithium aluminum hydride or lithium borohydride was employed, the product ratio of the two dihydro forms and the tetrahydro form depended largely on the substituent, and an especially high regioselectivity for the 3, 6-dihydro form was observed when the ortho substituent was hydroxyl or methoxyl group. The high regioselectivity was attributed to the reaction of the metal hydride with the ortho sustituent to form initially phenaxide or a coordinated bond, followed by intramolecular hydride attack to the 6 -carbon of the pyrimidinethione to yield 3, 6-dihydro-2(1 H)-pyrimidinethiones preferentially.

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As an extension of our investigation for the preparation of optically active phosphorus compounds using L-proline ethyl ester as a chiral source(Scheme 1), the asymmetric synthesis of phenylthiomethylphosphonic acid derivatives was undertaken. The phosphonate [4] and its precursor [1] were found to be good synthetic intermediates for the preparation of various optically active phosphonates.
A diastereomeri c mixture of phosphonamidates [1 a, b ] was prepared by the reaction of ethyl phenylthiomethylphosphonochloridate with L-proline ethyl ester, which was separated efficiently to give pure [1 a ] and [1 b] by silica-gel column chromatography. The absolute configurations of both [1 a] and [1 b] were determined by the chemical correlation to ethyl methyl methylphosphonate [3] as shown in Scheme 2.
Acid-catalyzed methanolysis of [1 a] and [1 b] afford ed (S)s, -[4] and (R)s- [4], respectively. The enantiomeric excess of [4] was determined to be no less than 97% using NMR shift reagent Eu(hfc)₃. The optically active [4] was converted to ethyl methyl alkylphosphonates [5] and [6] in fair yields (Scheme 3). The phosphonate [4] was also transformed to optically active alkenylphosphonates [7] and [8] (Scheme 4). The phosphonamidates [1 a ] and [1 b] were converted to the corresponding optically active 1-propenylphosphonamidates, (E)- and (Z)- [9 a] and [9 b ] by the reaction sequences shown in Scheme 5.

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Addition reactions of phosphorus compounds having a H-P bond with nitroalkenes gave C-P compounds. The functional group interconversions of the nitro group by the Nef and some other related reactions were unsuccessful. Reaction of ozone or singlet oxygen with the nitro group provided the corresponding aldehyde, which was further converted into the corresponding alcohol by reduction with sodium borohydride or sodium cyanotrihydroborate. The present method thus provides a new synthetic route for the preparation of β-hydroxy phosphorus compounds. Some phosphino sugar derivatives, i. e., 6-O-acetyl-5-deoxy-5-C(diphenylphosphiny1)-1, 2-O-isopropylidene-3-O-methyl-β-L-idofuranose, 1, 2, 4, 6-tetra-Oacetyl5-deoxy-3-O-methyl-1, 5-C-(phenylphosphinylidene)-L-idose, and 1, 2, 4, 6-tetra-O-acetyl -5-deoxy-3-O-methyl-1, 5-C-(methoxyphosphinylidene)-L-idose, were synthesize d from adducts of phosphorus compounds and the nitroenose derivatives. The latter two cbmpounds have the phosphorus atom in their hemiacetal rings.

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As a part of our studies to search for efficient hybridization probes, we synthesized partially self-complementary dodecanucleotides d(GGGAAF*NTTCCC)(N =T, C, A, G) containing a pyrrolo[2, 3-d]pyrimidine deoxynucleoside [7 a, dF*] by the solid-phase phosphotriester approach, and examined their properties. The hitherto-unknown nucleosides, 3-(β-D-2-deoxyribofuranosyl)pyrrolo[2, 3-d]pyrimidin-2(3 H)-one [7 a] and its 6-butyl derivative [7 b], which were fluorescent, were synthesized starting from a 5-iodo-2'-deoxycytidine derivative [3] via palladium-catalyzed coupling with trimethylsilylacetylene or 1-hexyne followed by copper-catalyzed intramolecular cycli'zation. From the measurement of thermal stabilitie s (Tm's) of dodecamer duplexes, it was found that F* base can pair only with G base and F*G base pair-containing duplex has a stability similar to that of the C⋅G base pair.

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Synthesis and reactivity of phosphorus tris(isocyanate), P(NCO)₃, were investigated. The compound was prepared from the reaction of phosphorus trichloride (PCl₃) with sodium cyanate (NaOCN) in the presence of several additives in benzene. It was found that the reaction was accelerated remarkably by the presence of an additive which facilitates dissolution of NaOCN in benzene, such as acetonitrile and succinonitrile.
P(NCO)₃ reacted with primary alcohols in a molar ratio of 1: 1 and 1: 2 to give the corresponding P(NCO)₂(OR) and phosphorus compounds bearing triazine skeleton [(NXCO)₃: X=H, -P(NCO)(NHCO₂R), -P(NHCO₂R)₂]. The reaction with a large excess of such al cohols provided the corresponding carbamates and allophanates, P(OR)₃, and phosphorus compounds containing -NCO, -OR, -NHCO₂R, and -NHCONHCO₂R group. On the other hand, the reaction of P(NCO)₃ with t-BuOH afforded phosphorus compounds having triazine skeleton [(NXCO)₃: X=-P(NC0)(NHCO₂But)], together with 1-butene formed by dehydration of t-BuOH and compounds containing>P-H and>P(O)H bonds. Mechanism of the reaction leading to these products is also discussed.

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Douglas Fir Tussock Moth (Orgyia pseudotsugata) sex pheromone has been synthesized as an application of tandem Wittig reactions of 1, 1-diphenylphosphorinanium bromide [1].
Methylthio group was introduced into α-position to phosphorus atom of [1]. Subsequent Wittig reaction of the resulting salt with decanal gave vinyl sulfide [4] in 56% yield. The Wittig-Horner reaction of [4 ] with hexanal followed by treatment with sodium hydride gave the diene [6] (21% yield based on [4]) as a precursor of the pheromone. Treatment of [6] with aqueous hydrochloric acid gave the desired pheromone [7] in 82% yield.

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Thermolysis of trans- and cis-1, 2, 3, 6-tetrahydro-1, 2-diphenyl-1, 2-diphosphorin 1, 2-disulfides [ 8 b] was carried out in the presence of 2, 3-diphenyl-1, 3-butadiene. [ 7 a] to give trans1, 2, 3, 6-tetrahydro-1, 2, 4, 5 -tetrapheny1-1, 2-diphosphorin 1, 2 -disulficie, [8 a], 3, 6-dihydro-2, 4, 5-triphenyl-2 H-1, 2-thiaphosphorin 2-sulfide [9 a]; and 1, 3, 4 -tripheny1-1-phospholene 1-su lfide [110a ] in 0-12, 8-26, and 0-7% yields, respectively. In the, cas of reaction of cis-[8 b]the isomerization to trans-[8 b] was also observed., A possible mechanism is proposed as follows: [8 b] undergoes the retro-Diels-Alder reaction to give J, 2-dipheny1-1, 2-diphosphene 1, 2-disulfide [4 a], which is trapped directly with [7 a] to afford [8 a], or dissociates to phenylphosphinothioylidene [6 a], which is trapped with [7 a], to give [9 a]and/or [10 a]

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The reaction of N-(1-phenylvinyl)iminotriphenylphosphorane [1 a] and N-(1-phenylvinyl)iminotributylphosphorane [1 b] with α, β-unsaturated ketones [2 a-e] an d with α-bromo ketones [14 a-j] were investigated. The compounds [1 a, b] underwent the Michael addition with [2 a-d] followed by aza-Wittig reaction to result in the formation of phenyl-substituted pyridines [3 a-d]along with acetophenone and phosphine oxides. The isolation of diketones [5 b, c] is a good evidence for the mechanistic aspect of the reactions. On the other hand, the reaction of [l a, b] with [2 e], which has neither methyl nor phenyl group on the carbonyl carbon atom, β-carbon atom of [l a, b]underwent a charge-controlled attack to thecarbonyl group to result in the formation of the pyridine [4 e]. In the reaction of [1 a, b]with α-bromo ketones [14 a-i], phenyl-substituted pyrroles [15 a-i] was obtained via a novel C-C bond formation followed by aza-Wittig reaction. However, [1 a]with ethyl bromoacetate [14 j] underwent no aza-Wittig reaction but instead a C-C bond formation to give [17j] was observed. The ₁H-NMR and ₁₃C-NMR spectra of [l a, b] also suggested the nucleophilic property of the β-carbon atom of the vinyl group.

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We succeeded in the synthesis of (2-oxocyclobutyl)diphenylphosphine oxide [4] via (1cyclobutenyptriphenylphosphonium salt [1] in good yield. Reaction of [4] with methanol gave methyl 4-(diphenylphosphinyl)butyrate [5] in 64% yield. Reaction of [4] with Schiff bases such as N-isobutylidenebenzylamine [6a], N-benzylidenebutylamine[6b], and N-benzylideneiso`proPylakriaine [6c] gave N-benzy1-5-(diphenylphosphiny1)-6-isopicipyl-2-pip e ridinone [7a] (28%), 4-(diphenylphosphiny1)-4-pentenamides [8a-c] (33-44%), and 4(diphenylphosphinyl)butyramides [9a, c] (24-32%), 'respectively. Reaction of [4] with diazomethane gave the ring-expansion products, (2-oxocyclopentyl)diphenylphosphine oxide (39-61%) and (2-methoxy-1-cyclopentenyl)diphenylphosphine oxide [11] (6-40%). Reaction of the enolate anion of the cyclobutanone [4]with diphenyl phosphorochloridate and benzoyl chloride produced enol esters of the cyclobutanone, [13] and [14], respectively, in good yields. Reaction of enol diphenylphosphate ester [13] with lithium dibutylcuprate ( I ) gave (2-butyl-1-cyclobutenyl)diphenylphosphine oxide CM) in 32% yield. The PielsAlder reactions of 3-substituted 2-diphenylphosphiny1-1, 3-butadienes, generated by thermolysis of (2-substituted 1-cyclobutenyl)diphenylphosphine oxides [14] and [15], with N-phenylmaleimide gave functionalized (1-cyclohexenyl)diphenylphosphine oxides [16] (28%) and [17](82%). Reaction of [4] with benzaldehyde did not give the Wittig-Horner reaction product, but 4-(diphenylphosphinyl)-5-phenyl-4-pentenoic acid [20] was obtained in 53% yield.

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The reactivity of intramolecular aza-Wittig type reactions of some selected ω-azido carbonyl compounds [2], [4] as well as ω-chloro acyl azides [ 6 ], was described. The starting azides were readily obtained by nucleophilic substitution reactions of the coesponding chlorides with NaN₃ under the phase-transfer-catalyzed conditions, and by the Michael addition reactions of HN₃ to α, β-unsaturated ketones.
The intramolecular aza-Wi ttig reactions proceeded readily for γ-azido ketone [2 c], and even for razido ester[2 d] and γ-chloro acyl azide [6 b], to give pyrroline, pyrrolidine systems respectively. On the other hand, the corresponding intramolecular reactions of [ 4], [2 b] and [6 a] to azetine, azetidine systems did not proceed under vigorous conditions. However, 2-phenyl-1-azetin [18] was given in very lower yield by the reaction of β-azidopropiophenone[2 a] with PPh₃, that was confirmed by an alternative synthesis from 1-phenylcyclopropyl azide [23] and by conversion to the corresponding azetidine [19].

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Upon UV-irradiation, some (substituted benzyl)phosphonic acids underwent easily C-P bond cleavage in a basic aqueous solution (pH 8 or above), resulting in the formation of corresponding substituted toluenes and orthophosphate. The photochemical C-P bond cleavage of nitro-, benzoyl-, and phenylsulfonyl-substituted derivatives were observed, but ethoxycarbonyl-, chloro-, di-phenylphosphinyl-, and phenyl-substituted derivatives were stable on irradiation. This photolysis may proceed via an intramolecular electron transfer from PO₃^2- group to substituted aromatic moiety to give a radical anion as a transient intermediate, which undergoes C-P bond cleavage to give substituted benzyl anion and monomeric metaphosphate ion. The photolysis of a 1: 2 molar mixture of p-(nitrobenzyl)- or p-(benzoylbenzyl)phosphonic acid and 1, 8-diazabicyclo[5.4.0]undec-7-ene in excess alcohol gave alkyl dihydrogenphosphate in fairly good yields.

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The crystal and molecular structure of the title compound was determined by the single crystal X-ray diffraction method. The crystal is monoclinic with the space group P 2₁/n, a=15.531(10), b=10.7 98(5), c=11.8 93(5)Å, β=91.27(4)°, Z=4, and the final R valu e obtained was 0.048. The antimony atom is bonded with three phenyl carbon and two 1, 1diolato oxygen atoms and has a deformed square-pyramid geometry (its summit is occupied by a carbon atom). The four membered ring is almost on one plane (average deviation of the respective atomic positions from the average plane is 0.022Å). Two Sb-O bonds are about the same in their lengths (2.037Å on the average), and they are regarded as covalent bonds. The bond lengths of C-0 are 1.383Å on the average, and the angles O-C-O', C-O(or O')-Sb, and O-Sb-O' are 105.6, 99.4 (on the average), and 65.45° respectively. These data show that the ring is not much deformed or stressed. The compound is stable and can be regarded as a heterocyclic compound rather than a metal chelate.

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α-Keto alcohols were oxidized into α-diketones with triphenylantimony dibromide [2 a] in the presence of two equiv. of base. The oxidation is rationalized by the sequence involving the base-catalyzed ligand exchange at apical position from bromine to a-keto alcohol to give hypervalent antimony [D] or stibonium bromide [E] which is followed by deprotonation at carbinyl position to furnish a-diketone directly with loss of triphenylstibine (path 1) or via hypervalent antimony [F] (path 2) (Scheme 2). Treatment of tri(p-tolyl)antimony dibromide [2 b] with 2-pyridone and triethylamine afforded bis(2-pyridyloxy)tri-p-tolylsantimony (V) [2 d] which was more effective for the oxidation without additional base (Scheme 3).
Finally antimony-catalyzed debromination and oxidation cycle was devised for the sys tem of α-keto alcohols and 2, 3-dibromo-3-phenylpropionate (bromine donor) (Scheme 4).

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Reduction of the ylides [1], [2] has been investigated by means of ESR and UV spectroscopies. Afterdis appearance of their short-lived anion radicals, trianion radicals ([4], [6]; Fig. 2c) produced by the reduction with alkali metal in THF were ob served. ESR data (g=2.0030) have shown and that the para position of the pyridine ring was reduced complet ely (see, Fig.1).

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Reduction of 7, 7-dibromobicyclo[4.1.0]heptane was examined in the presence of amine (triethylamine, tributylamine, N, N-diethylaniline etc. ) to evaluate dialkyl phosphonate (R=Me, Et, or i-Pr) as a reducing reagent. A combination of diethyl phosphonate and triethylamine was found to work efficiently for the selective reduction to 7-bromobicyclo[4.1.0]heptane as compared with other known debromination agents. Similarly gem-dibromocyclopropanes bearing the trimethylsilyl group were reduced to the corresponding monobromocyclopropanes under the present conditions.

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The reactions of 1-adamantyl azide [1 a], 2-adamantyl azide [1 b], , 2-methyl-2-adamantyl azide [1 c], , 3-homoadamantyl azide [1 d], , and bicyclo[3.3.1]non-1-y1 azide [1 e], with P(C₆H₅)₃ [2 a], , P(n-Bu)3 [2 b], 1 and P(OEt)₃ [2 c], were examined in order to prep are the corresponding iminophosphoranes. The relative reactivity of [1 a], in the reactions of [2a]-[2c], under reflux in benzene for 1 h was shown to be 1.0 0: 16.5: 8.50 based on the IR spectra. The relative reactivity of [2 a], in the reactions of [1 a]∼[1 e], under the same conditions as above was shown also as 1.00: 10.2: 0.58: 1.76. The corresponding iminophosphoranes [5 a], , [5 b], , and [5 c], from [1 a], with [2 b], and [2 c], , and from [1 b], with [2 a]respectively were obtained in high yields. Some examples of their applications on synthesis of adamantyl isocyanate, isothiocyanate, and carbodiimide, and/or their derivatives were also reported.

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A highly nucleophilic triarylphosphine, [2, 4, 6-(CH₃O)₃C₆H₂]₃P, was found to work as a convenient and excellent catalyst for the Michael addition reactions of CH₂=CHCN, CH₂=CHCOOCH₂CH₃, and CH₂=CHC(O)CH₃ with some nitroalkanes.

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In the presence of catalytic amount of palladium (Pd(PPh₃)₄, PhCH₂PdCl(PPh₃)₂), coupling reaction of dipropynyltrimethylantimony(V)[1] with acid chlorides took place to give only propynyl ketones [4] without concomitant formation of methyl ketones. An initial step of the coupling reaction may be the oxidative addition of [1] to Pd(O) at the propynyl-antimony bond.

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In an attempt to develop\ a functionalized organic metal, we have synthesized novel tetrathiafulvalene [6] and a ielated compound, 2-(4 H-thiopyran-4-ylidene)-1, 3-dithiole [7], which are fused with crown ether. They form crystalline 1: 1 charge-transfer complexes with strong r-electron acceptors such as TCNQ, TCNQF₄, DDQ, and HCBD. In addition, they form a complex with heavy metal salts, such as AgNO₃, CuCl₂, and PdCl₂. The electrical conductivities of these complexes are, however, semiconductive or insulating without exception. A single crystal X-ray analysis of [6]⋅TCNQ complex demonstrates that it has a unique stacking structure of alternate donor-donor-acceptor-acceptor sequence.

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Thioxyallyl which is a sulfur analogue of trimethylenemethane is thought to be an intermediate of cyclopropanethione-allene episulfide tautomeric system. However, there has been few studies for characterization of this system.
The MCSCF (multiconfigration self-consiste nt-field) studies of thioxyallyl intermediate showed that ¹B₁ state is more stable than ¹A₁ state, and is the lowest singlet state. This result suggests a striking contrast to the lowest ¹A₁ state of oxyallyl. Flash vacuum pyrolysis and thermolysis of both tetramethylallene episulfide [5] and 3, 3, 5, 5-tetram ethyl1-pyrazoline-4-thione [6] gave 2, 4-dimethyl-1, 3-pentadiene-3-thiol [7] via thioxyallyl intermediate [8]. Thermolysis of allene episulfide [5] is of first-order in unimolecular C-S bond cleavage of [7]. Solvent effects also appear on first-order rate co nstants and activation parameters, which may be due to the dipole moment of thioxyallyl intermediate [8]. Thermal reaction of allene episulfide [5] with carbonyl compounds gave 1, 3oxathiolane derivatives and pentadienethiol [7], whereas oxathiolane did not from in the reaction of 1-pyrazolinei-4-thione [6]. These results show that oxathiolane derivatives may be formed in direct reaction of allene episulfide [5], not via thioxyallyl intermediate. Reaction of diphenylcyclopropenethione [15] and 1, 3-diphenylisobenzofuran gave benzbthiophene derivative [19] via formation of cyclopropanethione [16] and its ring opening to thioxyallyl intermediate.
These resu lts suggest that thioxyallyl intermediate is a polarized biradical species, and is accordingly different from zwitterionic oxyallyl one.

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Eleven derivatives of orthocarbonate, spiroorthocarbonates and their sulfur analogues were synthesized to obtain their mass spectra. The molecular ion peaks were clearly observed for the spiro derivatives (eight samples) but hardly detected for the non-spiro derivatives (three samples). The sulfur analogues of the spiroorthocarbonates had much larger relative intensities of the molecular ions than the corresponding spiroorthocarbonates. Molecular ion peaks for aromatic spiroorthocarbonate and its sulfur analogue were observed as the base peaks. Fragmentation of the spiro derivatives was considered to proceed competitively via two of the three major pathways (Scheme 9) depending on the kind of the heteroatoms. Furthermore, the mass spectral differences between the oxygen and the sulfur derivatives and among the spiro derivatives bearing different number of ring members have also been studied.

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The structure and reactions of (phenylhydrazonomethylthio)alkanes (-N-N=CH-S-) were investigated and compared with those of (phenyliminomethylthio)alkane (-N=CH-S-). (Phenylhydrazonomethythio)alkanes were prepared by the reaction of (methylphenylhydrazono)methanethiol with alkyl halide. The structure of (phenylhydrazonomethylthio)alkane was investigated by ¹H-NMR, ¹³C-NMR, IR and UV spectroscopies and extended Hiickel molecular orbital calculations. (Methylphenylhydrazonomethylthio)ethane [2 a] and (phenyliminothylthio)ethane [1 a] were allowed to react with electrophilic, nucleophilic and oxidative reagents. The results were discussed in terms of different degree and mode of resonance stabilization of (phenylhydrazonomethylthio)alkane and (phenyliminomethylthio)alkane.

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The reaction of (methylphenylhydrazonomethylthio)ethane [1] with m-chloroperbenzoic acid(MCPB) in dichloromethane gave the corresponding sulfoxide [2] J and sulfone [3]The structures of [2] and [3] were investigated by ¹H-NMR, ¹³C-NMR, and IR spectroscopy. Unusual spectroscopic features of [2] and [3], were observed., Treatment of [2]with 98% sulfuric acid was found to give a purple solution which showed a UV absorption peak at 512.5 nm(max 9800). No coloration was observed with the [1] and [3]. The ESR spectrum of the colored solution was taken and the g value was determined to be 2.0083. It is strongly suggested that the g value is ascribed to the formation of sulfur centered cation radical, since almost identical g value was obtained for several sulfurcentered cation radical derived from diaryl sulfoxides. It is noted that the ESR signal of the colored solution was detected in sulfuric acid over 70% concentration and was stable for 10 days at least. The results were discussed in terms of different degree and mode of resonance stabilization and stability of cation radical by the use of extended Hückel molecular orbital calculations. Consequently, a possible explanation for this may be that the unusual spectroscopic features of [2] and [3] can be ascribed to the different degree of resonance structure, and that the rather stable cation radical is formed by the unimolecular fission of the sulfur-oxygen bond, perhaps via the resonance stabilized structure of butadiene type (3 pir-2 pr-2 pr-2 pr) in which both the 7r-electron and p-electron on sulfur atom are drifted to nitrogen atom.

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The structures of 5-oxo- and 5-hydroxy-substituted 5, 6-dihydro-4-phenyl-4 H-1, 3, 4thiadiazine, [1] and [2], were discussed in terms of resonance stabilization based on the spectral data and the extended Hckel molecular orbital calculations. The structures of [1]is best interpreted by weak combination of two adjacent, local resonance structures of 3π-2π-2πr(-S-C=N-) and 2π-2π2π(-N-C=O). On the other hand, [2] takes single butadiene-type resonance structure of 3π-2 π-2 π-2π(-S-C=N-N).
As to the chemical properties, while [1] was ine r t to electrophiles, nucleophiles and radical reagents, [2] was unstable to weak acids and other electrophiles giving hardly separable complex mixtures. Treatment of [2] with alcohols, thiols and amines readily gave, however, the corresponding 5-alkoxy-, 5-alkylthio- and 5-alkylamino-4-phenyl-5, 6dihydro-4 H-1, 3, 4-thiadiazines in almost quantitative yield.
The high reactivity of [2] towards electrophiles an d nucleophiles may be ascribed to the resonance stabilization of the carbocation intermediate, 5, 6-dihydro-4 H-1, 3, 4-thiadiazinium cation, formed by heterolysis of the carbon-oxygen bond.

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A new phosphonium salt, (triphenylphosphonio)methyl 1-pyrrolidinecarbodithioate bromide [7], was prepared from the reaction of (bromomethyl)triphenylphosphoniurn bromi[de and pyrrolidinium 1-pyrrolidinecarbodithioate in 85% yield.
Treatment of the salt [7] with potassium t -butoxide at 0°C in tetrahydrofuran gave a yellow solution of the ylide [8], which reacted with various aldehydes and activated ketones, such as biacetyl, benzil, and methyl pyruvate, to give the corresponding vinyl esters [9] in moderate to high yields (Table 1).
It was found that the ylide [8] is rather stable than the ylides [10] and [11], which were generated from (triphenylphosphonfo)methyl arenecarbothioate bromides [5] and carbodithioate iodides [ 6 ].
The reaction of [9] with some nucleophiles was investigated (Table 2). The esters [9] were converted to the corresponding vinyl sulfides [4] via the alkenethiolates [3]by treatment with n-BuLi, followed by alkylating agent.

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A new cyclic sulfur ylide, 8-methyl-1, 3-diphenyldibenzo[b, f]cyclopenta[d]thiepinio-2-ides [8 a]was synthesized by deprotonation of the thiaazulenium sa [lt [7 a] with sodium hydride. Other 81-alkyl derivatives were generated in situ and subjected to thermal reactions. The ylide [8 a] underwent 1, 4-rearrangement to give 3 a-methyl-1, 3-diphenyl-3 ali-dibenzo[b, cyclopenta[ d ]thiepin [11 a] (64%) together with the demethylated product [ 6 (12%), whereas S-ethyl [8b]and 5-propyl derivative [8 c] afforded the 1, 4-rearranged product 11b] (34%), [11 c] (14%) and the 1, 2-rearranged product [12 b] (29%), [12 c] (47%), respectively.
This 1, 2-rearrangement is unique and interesting because it proceeds at a cost of the benzenoid stabilization of a condensed benzene ring.

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Tetrakis(alkylthio)thieno[3, 4-c]thiophenes containing a 10 π electron nonclassical condensed thiophene nucleus were prepared by the dimerization' reaction of bis(alkylthio)cyclopropenethiones. The thermodynamical stability and unreactibity toward oxgen are interpreted in terms of the substituent effects of alkylthio groups. Since the low oxidation potentials were observed by cyclic voltammetry, the charge-transfer complexes of [1] with several acceptors were prepared and the properties were examined.

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Selective and facile synthesis of benzene ring-substituted benzimidazolones, benzoxazolones and benzothiazolone was successfully accomplished in good yield by reductive carbonylation of the corresponding o-substituted nitrobenzenes with elemental sulfur, carbon monoxide and water in the presence of triethylamine.
The reaction of elemental s u lfur with carbon monoxide in the presence of triethylamine may initially afford carbonyl sulfide, which reacts with water to give the mixture of hydrogen sulfide and carbon dioxide under the reaction conditions.
Therefore, the present reactions probably took plac e through initial reduction of the starting nitrobenzenes with hydrogen sulfide followed by intermolecular cycloaddition of the resulting aniline derivatives with carbonyl sulfide generated in situ under the reaction conditions.
The reaction did not occur in the absence of either triethylamine or water.

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Reductive elimination reactions of β-nitro sulfides with sodium sulfide or tributylstannane provide a new method for the preparation of olefins. α-Nitrostilbenes, which are prepared by the condensation reactions of aldehydes with nitro compounds, are converted into stilbenes on treatment with sodium sulfide in the presence of thiophenol. The reaction proceeds very rapidly at room temperature to complete within 5 min. Allyli calcOhols are readily prepared by the tributylstannane-promoted elimination reaction from γ-phenylthio β-nitro alicohols, which are prepared by the reaction of nitro olefins with thiophenol and aldehydes in the presence of a catalytic amount of a base.

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The dianions of heteroatom-substituted 2-methylpropenamides were generated at -78°C. Among the dianions studied, the reagent formed from N-phenyl-2-[(phenylsulfonyl)methyl] propenamide exhibited a high regioselectivity toward a wide variety of electrophiles in tetrahydrofuran (THF).
The α-adducts prepared from the dianion and alkyl halides gave stereoselectively (E)-2methyl-2-alkenamides on brief treatment with sodium borohydride in ethanol. The corresponding sequence using aldehydes and epoxidesa fforded( E)-4-hydroxy-2-methyl-2-alk. enamides and (E)-5-hydroxy-2-methyl-2-alkenamides, respectivelyu nder similar reaction, c onditions.5, 6-Dihydro-2 H-pyrans were prepared by treatment of α-adducts, obtained from the dianion of N-phenyl-2-[(phenylsulfonyl)methyl]propenamide and epoxides, with potassium t-butoxide in THF.

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Treatment of aromatic aldehydes with dialkyl sulfides-alkyl halides under benzene-aqueous NaOH solution (liquid-liquid two phase) or solid KOH-CH₃CN (solid-liquid two phase systern)produced oxiranes in moderate to good yields in one pot. In these procedures, it was demonstrated that sulfides worked as mediators which could transfer alkyl groups to the aldehydes while the sulfonium salts play a role as phase-transfer catalysts.1, 5-Dithiacyclooctane was found to promote remarkably the reactions. Scope and limitations of the reactions as a synthetic method for oxiranes were also described.

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The solid-state reaction of the ground mixture of 1, 2, 2, 6, 6-pentamethyl-4-oxothianium tetrafluoroborate [ 3] with some alkali metal halides has been examined in comparison with the corresponding reaction in aqueous solution. Each ground mixture was prepared by a mill or an agate mortar. At room temperature, changes were recognized in the infrared spectra as the time proceeds in KC1 and KBr, but were little observed in KI and NaCl. The reaction of [3] with KCl occurred via ion exchange and afforded mainly 2, 6-dimethy1-6methylthio-2-hepten-4-one [4], α β-elimination product, and 2, 6-dichloro-2, 6-dimethy1-4heptanone [6]an HCl adduct of 2, 6-dimethyl-2, 5-heptadien-4-one [5]. On heating the system, the chief product was [4] in KCl and NaCl. In KBr, products were [4], 2, 2, 6, 6tetramethylthian-4-one [8] and [5]. The reaction products in KI were nearly exclusively [8] which was formed by the attack of S-methyl group at the oxothianium ring. On the other hand, the reaction in aqueous solution afforded only [4]for all alkali metal halides employed. Based on the facts described above, it became clear that the reactions in the solid state are different from those in solution, and that chloride, bromide and iodide ion act as hard, borderline and soft base, respectively. Furthermore, it was found that the reactivity of halide ions was changed by the substituent group on 2- and 6-position of the 4-oxothianium ring.

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Sulfonium tribromides have been found to brominate trans-stilbene effectively in solid state reactions. When the ground mixture of 1-methylthianium tribromide and trans-stilbene in an agate mortar was stored in a thermostat, at 30°C for 2 d, meso-1, 2-dibromo-1, 2-diphenylethane (meso-stilbene dibromide) was obtained quantitatively and stereoselectively (transaddition). Several other sulfonium tribromides also gave similar results, though the reaction time needed for completion varied. Examination of the progress of the reaction of 1rnethylthianium tribromide by infrared absorption spectrometry and powder X-ray diffraction indicated that the crystals of trans-stilbene gradually change to those of meso-stilbene dibromide, while those of the sulfonium tribromide to those of the sulfonium bromide.

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The thermal and the photolytic decomposition of tosylhydrazones of tetrahydro-4 H-thiopyran4-one [2] and dihydro-2 H-thiopyran-3(4 H)-one [4] were studied. In the thermal and the photolytic decomposition of [2] and [4] cyclic olefins were produced. In the case of [4], α, β-unsaturated olefin was predominated over β, γ-unsaturated one in the thermal decomposition in the presence of sodium hydride in diglyme and the photolytic decomposition in the presence of sodium in ethylene glycol, as shown in eqs. (6) and (9).
On the other hand, in the case of [2] the corresponding azine afforded as a major product in the thermal decomposition in the presence of sodium methoxide in ethylene glycol and the photolytic decomposition in the presence of sodium hydride in diglyme, as shown in eqs. (3) and (4).
The mechanism which may explain the formations of the observed products were discussed.

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Low-pressure pyrolysis technique was used to study the thermal decomposition of thiirane and thiolane at pressure 10^-2 Pa and the temperature up to 1100 K (Table 1). Thiirane decomposed above 900 K (Fig.1) to yield ethylene stoichiometric ally (Table 2). RRK unimolecular reaction theory was applied to interprete the results. Arrhenius A factor was estimated as shown in Table 3. The best fit to the experimental rate constants kuni was obtained when the following high pressure Arrhenius parameters were assumed (Fig: 2).
k=10^13.2exp(-171(kJ⋅mol^-1)/RT)s^-1
The estimation of thermodynamic properties of 2-thioethyl biradical (Table 4) indicated that'the obtained activation energy is too low to form the biradical as an intermediate. To verify whether this low activation energy is characteristic for the decomposition of thiirane, we studied thiolane under similar conditions.
Thiolane decomposed above 900 K (Fig.3) to yield propylene and ethylene as main products (Table 5). By using the procedure as employed for thiirane, the A factor was estimated as shown in Table 6, and the high pressure Arrhenius parameters were obtained (Fig.4).
k=10^15.6exp(-301(kJ⋅mol^-1)/RT)s^-1
The estimation of thermodynamic properties of the 4-thiobutyl biradical (Table 6) indicated that the obtained activation energy is in excellent agreement with the enthalpy change for the formation of 4-thiobutyl biradical. Accordingly the following biradical mechanism may well explain the decomposition of thiolane.
Thus we conclude that the unusually low activation energy is characteristic to thiirane. We proposed an alternative mechanism in which thiirane decomposes through triplet state rather than through biradical formation as reported previously.

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Aryl(o-phenylaryl)thione S-imides were formed by reaction of the corresponding thioketones with chloramine salts. The thione S-imides further underwent electrocyclization followed by the Stevens-type rearrangement involving intermediary cyclic sulfur ylides, to give Nphenyl sulfonyl- and N-tosy1-9-ary1-9-fluorenesulfenamides. The reaction of the thione containing a mesityl substituent gave E-isomers of thione S-imides stereoselectively. On the contrary, , both geometrical isomers of sulfines were obtained by oxidation of the thiones with m-chloroperbenzoic acid. E-isomers of the sulfines stereospecifically underwent electrocyclization followed by rearrangement in the presence of catalytic AlCl₃, whereas the Z-isomers were unreactive under these conditions. This reaction involved the Pummerer-type rearrangement of intermediary cyclic sulfoxides.

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Reactions of 2, 3-diphenylthiirene 1-oxide [1] with several nucleophiles and with 1, 3-dipoles were investigated to compare with those of the corresponding thiirene 1, 1-dioxide. In the reaction with α-lithioisobutyronitrile, 5-imino-4, 4-dimethyl-2, 3-dipheny1-2-thiolene 1-oxide was formed in a good yield via nucleophilic attack of the carbanion to the ring carbon of [1] followed by recyclization of the resulting sulfenic acid intermediate. When a nitrile, bearing an α-hydrogen such as α-sodiobenzyl cyanide reacted, an acyclic product, 2, 3, 4tripheny1-2-butenenitrile, was obtained through rearrangement of a sulfenic acid intermediate to a more stable olefin and SO elimination. Nucleophilic cycloaddition was observed in the reaction with N-(2-methy1-1, 3-pentadienyl)piperidine to give 3, 5-dimethy1-1, 2-dipheny1-6 piperidino-1, 3-cyclohexadiene and 3, 5-dimethyl-1, 2-diphenylbenzene in 12 and 5% yields, respectively. Furthermore, 1, 3-dipolar addition with C, N-diphenylnitrilimine and benzonitrilium p-nitrobenzylide afforded 1, 3, 4, 5-tetraphenylpyrazole and 5-(p-nitrophenyl)-2, 3, 4triphenylpyrrole in 49 and 57% yields, respectively. Though the monoxide [1] showed a reactivity pattern similar to those of the thiirene dioxide, the reactivity of [1] was relatively lower than that of the dioxide.

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In order to clarify the effect of electron-releasing property of substituents on the hydrodesulfurization, the ortho, meta and para isomers of aminobenzenethiol, methoxybenzenethiol and toluenethiol were hydrogenolyzed by a batch method at 160∼240°C and H₂ (40 atm) over molybdenum(M) sulfide catalyst. Benzothiazole and phenothiazine were also reacted un der the similar conditions.
Hydrogenoly ses of aminobenzenethiols at 160°C (Table 2), methoxybenzenethiols at 200°C (Table 3), and toluenethiols at 240°C (Table 4) yielded appreciable amounts of aniline, anisole/phenol, and toluene, respectively, as the main hydrodesulfurization products. Among the isomers of these ring-substituted benzenethiols, the easiness of the hydrodesulfurization by the C-S bond cleavage was found to be in the order of para>ortho>meta isomer, approxiMately. Furthermore, in the case of the para-substituted benzenethiols, the easiness of the hydrodesulfurization resulted in the following order: p-aminobenzenethiol>>p-methoxybenzenethiol>p-toluenethiol=benzenethiol at 160°C, and p-toluenethiol>>benzenethiol at 240°C. These results indicate that the hydrodesulfurization of the ring-substituted benzenethiols are promoted to a great extent when high electron-releasing substituents like amino and methoxy l group exist in the para or ortho position of benzenethiols. The promoting effect of the substituents on the reaction might be attributed to the increase of the electron density on the electron acceptable sulfur atom by the presence of the electron-releasing substituents making these substrates to be easily adsorbed on the anion vacancy of the catalytic surface through the sulfur atom.
In the hydrogenoly s es of benzothiazole and phenothiazine, the selective cleavage of C-S bond on benzene ring took place easily at 280°C (Table 5) in a similar manner as the above stated hydrodesulfurization of p- or o-aminobenzenethiol. It was suggested that the hydrodesulfurization of these heterocyclic compounds were extremely accelerated by the presence of ring-substituted nitrogen atom in the ortho position, compared with the hydrodeoxygenation of oxygen analogues presented before.

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