The effects of various additives on the regioselectivity in the reactions of ally! dithiocarbamate with aldehydes were examined. The lithium salt of allyl dithiocarbamate reacts with aldehydes in the 'absence of an additive to give γ-adducts exclusively. However, the reactions in the presence of some additives, especially of Ti(OPrⁱ)₄, afford α-adducts in a regioselective manner. These reactions are explained by assuming a 6-membered chair form transition state, involving a titanium atom.

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DBU absorbs CO₂ effectively at room temperature in the presence of water or alcohol. Subsequently, DBU carbonate salts produced react with alkylating reagents to form the corresponding dialkyl carbonates in fairly good yields under mild reaction conditions.
On the other hand, the mixture of water, CS₂, and DBU (molar ra tios 2: 3: 4) gives 2moles of DBU trithiocarbonate salt, with evolution of 1 mole of CO₂, by heating at 80°C and the reaction of the resulting salt with alkylating reagents affords dialkyl trithiocarbonates in good yields.
The main difference between the above two cases could be ascribed to the stronger nucleophilicity of the preformed anion of sulfur than that of oxygen.

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Stereocontrol in baker's yeast-mediated reduction of β-keto esters was successfully achieved by introducing the sulfenyl functionalities at α-position of the esters to afford optically pure (3 S)-hydroxy esters, such as ethyl (3 S)-hydroxy-2-(methylthio)butanoate [2 a], ethyl (3S)-hydroxy-2-(methylthio)pentanoate [2 f], ethyl 5-benzyloxy-(3 S)-hydroxy-2-(methylthio)pentanoate [2 g]. Reduction of α-alkyl β-keto dithioester derivatives with baker's yeast afforded asymmetric reduction products having S configuration, methyl (2 R, 3 S)-3-hydroxy-2methyldithiobutanoate [7 a] and (1 R, 2 S)-2-[(methylthio)thiocarbonyl]cyclohexanol [7b], with high enantio- and threo diastereoselectivity. The utility of the present method was demonstrated in the stereoselective synthesis of the sex attractant of pine saw-fly, (2 S, 3 S, 7 S)-2-acetoxy-3, 7-dimethylpentadecane [10] from two optically pure hydroxy esters, [2 a] and [7 a].

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The reaction of dimethyl acetylenedicarboxylate (DMAD) with elemental selenium in a molar ratio of 2: 1 in refluxing o-dichlorobenzene for 6 h afforded tetramethyl 2, 3, 4, 5-selenophenetetracarboxylate in 54% yield. Although the use of DMAD in excess afforded an improved yield (65%) of the selenophene, the reaction was accompanied by the formation of an appreciable amount of trimethyl 5-methoxy-2, 3, 4-furantricarboxylate as by-product, which resulted from the self-condensation of DMAD. Heating of methyl propiolate with elemental sulfur in a molar ratio of 5: 1 in benzene at 205∼215°C for 14 h in a stainless steel autoclave afforded dimethyl 2, 4- and 2, 5-thiophenedicarboxylates in 41 and 19% yields, respectively, while heating with elemental selenium under the same conditions gave dimethyl 2, 4- and 2, 5-selenophenedicarboxylates in 45 and 30% yields, respectively. The proposed mechanism involves the initial formation of 1, 2-dithiete(1, 2-diselenete)intermediates from acetylenes and elemental sulfur (selenium). These intermediates, after ring-opening, undergo cycloaddition with acetylenes to give 1, 4-dithiins(1, 4-diselenins) which eliminate sulfur (selenium)to give the observed final products.
Benzyne, generated by t hermal decomposition of diphenyliodonio-2-carboxylate in boiling o-dichlorobenzene reacted with elemental sulfur to give thianthrene (5%) and benzopentathiepin (6%), and reacted with elemental selenium to give selenanthrene (26%). The formation of thianthrene and selenanthrene provides, though indirect, an evidence for the intermediacy of (1, 4-diselenins) as intermediates in the foregoing reactions.

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4-Biphenylselenocarboxylic acid [6], selenium isologue of 4-biphenylcarboxylic acid, was synthesized by the reaction of hydrogen chloride in ether with sodium 4-biphenylselenocarboxylate [4']prepared from bis(4-biphenylcarbonyl) diselenide [3] and sodium methoxide. The spectral data of [6], a red solid of mp 39.0∼40.0°C, were specified. [6] changed to [3] by heating, and to bis(4-biphenylcarbonyl) selenide [7] and [3] by heating in hexane. [6]reacted with methanol to give methyl 4-biphenylcarboxylate, [7], and C3 J. Th[6e] reaction of [6] with phenylisocyanate to gave phenylcarbamoyl 4-biphenylselenocarboxylate[13]and with aniline gave 4-biphenylcarboxanilide [14]. [13]changed to [14] by heating.1Adamantaneselenocarboxylic acid (yellow solid of mp 28.0-∼29.0°C) was also synthesized by the same manner as the preparation of [6] and its spectral data were specified.

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Optically active diaryl selenoxides have been prepared by either asymmetric oxidation of diaryl selenides or optical resolution of diastereomeric aryl p-(l-menthyloxycarbonyl)phenyl selenoxides. Ena. ntiomerically pure selenoxide has been synthesized for the first time by ester exchange of the diastereomerically pure 1-menthyl ester with sodium methylate. Diaryl selenoxides with bulky ortho substituents were found to be stable toward thermal racemization. Optical purity of the asymmetric diaryl selenoxides was found to be determined by HPLC using optically active column.

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Acylation of amino groups under mild conditions is important in the synthesis of alkaloids and amino glycosides. We found that S-acyl Se-phenyl selenosulfides (SSe-phenyl (selenothioperoxy)carboxylates) [1] which could be easily prepared from thiocarboxylic acid and N-(phenylseleno)phthalimide, served as the active acylating agent. Reaction of an amine with the selenosulfide [1] gave rather poor yield of the amide, but we examined various additives for this reaction and found the addition of mercury(II) acetate remarkably increased the yield. Thus, primary amines such as benzylamine, pyrrolidine as a secondary amine, and amines with a hydroxyl group such as 2-aminoethanol can be readily acylated at ambient temperature. Diamines such as putrescine and cadaverine, and spermidine were dibenzoylated. Maytenine was synthesized from spermidine and S-cinnamoyl Se-phenyl selenosulfide. Selenosulfides [1] have been found to be effective acylating agents which can react with various amines under mild conditions to give the corresponding amides.

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A convenient synthetic procedure for penam-type β-lactams utilizing methylseleno-promoted ketene-imine cycloaddition reaction has been developed. Several alkoxyketenes [11 a, d] were treated with racemic and optical active alkyl 2-methylseleno-2-thiazoline-4-carboxylates [6]∼[8] to give the C 5-methylseleno-substituted penams [12]∼[16] and [33] in a highly stereoselective manner and in good yields. Reductive demethylselenation of compounds [6]∼[8] and [33] by treating with (n-Bu)₃ SnH in refluxing THF and MeCN or in THF and MeCN at 60°C in the presence of AIBN furnished the corresponding racemic and optically active penams [17]∼[20], [22], and [34]. Some of these penam esters were successfully converted to new penamcarboxylic acids [32], [37] and the potassium salt derivatives [31], [35].

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Synthesis of selenium and tellurium derivatives of thiocarboxylic acid which are interesting synthetically and biologically has not been described in literature, except for SeS-aryl (selenothioperoxy)carboxylates and TeS-aryl (telliiirothioperoxy)crboxylates. As a part of our study concerning synthesis of new thio- and dithiocarboxylic acid derivatives, synthesis and reaction of the title's compounds were investigated. Reactions of potassium or piperidinium thiocarboxylates with selenium tetrachloride or sodium selenopentathionate and with tellurium tetrachloride or sodium telluropentathionate were found to give selenium [1] and tellurium bis(thiocarboxylates) [2] in moderate yields. The obtained [1] and [2] are colorless or pale yellow crystals and relatively stable at room temperature. Both [1] and [2] react with chlorine, bromine, and iodine at 0°C to give the corresponding diacyl disulfides. The reaction with, halogen, followed by the addition of piperidinium dithiocarboxylate, afforded the unsymmetrical acyl thioacyl disulfide together with diacyl disulfide and selenium or tellurium bis(dithiocarboxylates). Whereas, the reaction of [2] with bromine at -30°C afforded the crystalline adduct, dibromotellurium bis(thiocarboxylates), which decomposes to give acylthio bromide. On the basis of these, results, possible reaction mechanism, where halogen attacks initially selenium or tellurium atom and then the S-Se or 5-Te bond is cleaved to give acylthio halide (RCOSX, X=halogen) and acylthioseleno or acylthiotelluro halides (RCOSEX, E=Se or Te, X=halogen), was proposed.

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Elemental selenium and tellurium were found to catalyze the formation of thiophene derivatives in the reaction of elemental sulfur with alkyne (dimethyl acetylenedicarboxylate [1 a] and diphenylacetylene [1 b]). In the reaction of 100 mmol of [1 a] with 40 mmol of S at 110°C for 24 h in the absence of selenium or tellurium, the yield of tetramethyl 2, 3, 4, 5-thiophenetetracarboxylate [2 a] was 5%, while the yields of [2 a] in the presence of 0.04, 0.48, and 4.0 mmol of Se were 22, 39, and 53%, respectively. Elemental tellurium acted as a catalyst. In the similar conditions the yield of [2 a] in the presence of 0.2 mmol of Te was 38%.
In the thi ophene forming reaction catalyzed by (η-cyclopentadienyl) (1, 5-cyclooctadiene)cobalt(I) [4], elemental selenium promoted the reaction. The yield of [2 a] was 75%in the reaction of 100 mmol of [1 a] with 40 mmol of S at 110°C for 24 h in the presence of 0.2 mmol of [4] and 40 mmol of Se.
In the reaction of [1 b] p (25 mmol) with S (10 mmol) at 140°C for 24 h, the presence of 10 mmol of Se increased the yield of 2, 3, 4, 5-tetraphenylthiophene from 2% (in the absence of Se) to 10%.

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Various alkyl phenyl tellurides are prepared by several methods, one of which consists of a newly developed Michael-type addition of benzenetellurolate anion to alkenes having an electron-withdrawing substituent such as CO₂Et or CN. Treatment of these tellurides with carbon monoxide (1∼20 atm) in acetonitrile or methanol in the presence of a palladium (II) salt such as Li₂PdCl₄, PdCl₂ or Pd(OAc)₂ affords benzoic acid or methyl ben zoate as a main product together with the corresponding alkenes and a small amount of alkanoic acids or their methyl esters. Similar reaction of didodecyl telluride results in a predominant formation of I-dodecene. The migration of phenyl or alkyl group from tellurium to palladium(transmetallation) at the initially produced telluride-palladium(II) complex to giv e a reactive organopalladium species followed by CO insertion or β-elimination is proposed as one of the possible reaction pathways.

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Dibenzoyl ditelluride [1], tellurium analogue of benzoyl peroxide, was synthesized by the reaction of benzoyl chloride in ether with sodium hydrogentelluride prepared from tellurium and sodium borohydride in water. IR and ¹³C-NMR spectra of [1] were compared with those of dibenzoyl diselenide [1], selenium analogue [1] reacts with water to give tellurium and benzoic anhydride, and with ethanol to give tellurium and ethyl benzoate by the path (scheme 2), with involves pertellurocarboxylic Te-acid and Tellurocarboxylic Te-acid as intermediates. [1] seems to eliminate tellurium by the reaction with triphenylphosphine.

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Benzenetellurenyl benzoate was synthesized by the reaction of silver or sodium benzoate with benzenetellurenyl bromide in benzene prepared from diphenyl ditelluride and bromine, and also by the reaction of diphenyl, ditelluride, benzoic acid, and t-butyl hydroperoxide. Benzenetellurinyl benzoate was forted as a by-product in both reactions. Benzenetellurenyl benzoates with p-substituents on either benzene ring were also synthesized by the same manner. Some reactions of benzenetellurenyl benzoates were studied.
Benzenetellurenic and p-substituted benzenetellurenic acids were prepared by hydrolyses of the corresponding benzenetellurenyl benzoates, and also by the reactions of the corresponding ditellurides and t-butyl hydroperoxide. Some reactions of tellurenic acids were studied.

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Sodium telluride, prepared by heating tellurium and sodium hydride in a 1: 2 molar ratio in dry N, N-dimethylformamide, readily debrominates a bromoacetic ester [2] at low temperatures to generate an ester enolate anion [13], which undergoes a Reformatskytype reaction with various nonenolizable aldehydes [1] to give the corresponding α, β-unsaturated esters [3] in good to moderate yields. Haloacetonitrile [4] reacts similarly to afford α, β-unsaturated nitriles [5] in moderate yields. Although the results were unsatisfactory with N, N-dialkylbromoacetamides [7], N, N-dialkyltrichloroacetamide was found to produce N, N-dialkyl- p p-aryl- α-oxopropionamides [10] as a major product. On a similar treatment, 4-cyanobenzyl bromide [11] condenses with piperonal in a reductive way to give 4'-cyano-3, 4-methylenedioxystilbene [12] among other products.

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The reduction of benzenetellurol has been studied in detail. Benzenetellurol is generated in situ by methanolysis of phenyltellurotrimethylsilane
. Since the conversion is rapid and the sole by-product, methyl trimethylsilyl ether, does not interfere with the reaction of benzenetellurol, this provides a method of choice for examining the reactivity of benzenetellurol itself under neutral conditions.
A variety of nitro com pounds were smoothly reduced with benzenetellurol to the corresponding amines at room temperature in benzene (Table 1). Aldehydes and phenyl ketones were similarly converted into primary and secondary alcohols, respectively (Table 4). Moreover, olefinic or acetylenic compounds conjugating with a phenyl or carbonyl group were hydrogenated by benzenetellurol (Table 5). Effects of sunlight (Fig.1), reaction temperature, and additives (Table 8) on reduction of carbonyl and olefinic compounds suggested that these reactions proceeded via a mechanism involving initial electron transfer from benzenetellurol to substrate (Scheme 3).
On the other hand, secondary alkyl tellu rides were converted into alkanes via thermal or photoinduced radical process (Table 6, Scheme 4). Primary alkyl tellurides resisted the reduction. Acetals were not reduced with benzenetellurol under normal conditions but to the corresponding ethers in high yields by using ZnI₂ as a catalyst (Table 7).

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2-Aminobenzothiazoles [2] were prepared by the reaction of electrogenerated thiocyanogen with aromatic amines [1], Electrochemical reaction was carried out by passing 5F/mol electricity under a constant current in aqueous acetic acid containing ammonium thiocyanate at 5∼10°C.

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The reaction of 4, 4-dimethylthiete 1, 1-dioxide [1] with carbanions was studied in comparison with those of three-membered and acyclic α, β-unsaturated i sulfones. The reaction of [1] with α-sodiodiphenylacetonitrile gave a Michael addition product, while the ring of [1]was cleaved to form 3-cyano-3-phenylallyl isopropyl sulfone when treated, with α-sodiophenylacetonitrile. In the reaction with ethyl α-sodiophenylacetate, , [1] gave an allyl sulfone derivative as well as a dihydrothiopyranone 1, 1-dioxide derivative.

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The reductive thiolation of aromatic ketones and aldehyde has been investigated. Hydrogen sulfide, generated in situ from elemental sulfur, carbon monoxide, and water, reacted with various aromatic ketones and aldehyde to give the corresponding thiols in moderate to good yields.

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Reaction of dibutyltelluronium (isobutylcarbamoyl)methylide with aldehydes gave α, β-unsaturated carboxamides with high E-selectivity and good yields. When reacted with trans-2-octenal, this reagent afforded pellitorine ((2 E, 4 E)-N-isobutyl-2, 4-dodecadienamide)in 71% isolated yield.

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Stereo- and regioselectivity of the addition of benzenetellurolate ion (PhTeNa), formed in situ from (PhTe)₂, and NaBH₄ in ethanol, to acetylenic bonds have been studied. Its addition to monosubstituted acetylenes such as phenylacetylene, 1-octyne, and propargylic alcohols proceeded completely in a trans fashion to afford a regioisomeric mixture of the corresponding vinylic tellurides, the attack of PhTe moiety occurring mainly at the terminal carbon (terminal/internal=ca.80∼90/10∼20) except the case of phenylacetylene where the ion attacked completely the terminal carbon. No reaction was observed with 4-octyne, while diphenylacetylene afforded a low yield of the addition product. In the case of propiolic acid esters the addition of PhTe moiety occurred completely regioselectively at acetylenic β-carbon, while a small amount of cis-addition product was always formed (trans' cis= ca 95/5). Benzenetellurol(PhTeH), formed in situ by methanolysis of (phenyltelluro)trimethyl. silane, showed a very low reactivity for this addition.

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