The electrochemical fluorination of dithiols [1,4-butanedithiol (I), 1,5-pentanedithiol (II), and 3-oxapentane-1,5-dithiol (III)] and cyclic sulfides [tetrahydrothiophene (IV), 2-methyltetrahydrothiophene (V), 3-methylthiophene (VI) and tetrahydrothiopyran (VII)] was conducted. Dithiols afforded the corresponding fullyfluorinated analogs of the starting dithiol (SF5(CF2)n SF5; n=4 from 1,5 from II; SF5CF2CF2OCF2CF2SF5 from III) and the cyclic products (perfluorotetramethylenesulfur tetrafluoride from I, perfluoro-2-methyltetramethylenesulfur tetrafluoride, perfluoro-3-methyltetramethylenesulfur tetrafluoride, and perfluoropentamethylenesulfur tetrafluoride from II, and perfluoro-4-oxapentamethylenesulfur tetrafluoride from III). The corresponding perfluoro-cyclic sulfur(VI) compounds were obtained from IV, V, VI, and VII in reasonable yields. The novel perfluoropolymethylene bis(sulfur pentafluoride)s are transparent heavy liquids. Their physical properties and 19F NMR and IR data are reported.
Novel conversions of pyrrolo-pyrimidines into pyrimido-pyrimidines are described. The treatment of 5-nitrosopyrrolo-pyrimidine (I) under Beckmann conditions causes ring expansion to give pyrimido-pyrimidine (II). Both the reduction of I with triphenylphosphine, potassium pyrosulfite, or sodium dithionite in dimethylformamide and the oxidation of 5-aminopyrrolo-pyrimidine with lead tetraacetate in dimethylformamide or acetic acid afford II. 5-Aminopyrimido-pyrimidine is prepared by the nucleophile-induced ring expansion of I. The possible mechanisms of these ring expansions are proposed.
Aluminum chloride-catalyzed reactions of β-lactones with acid chlorides were studied. 3-Propanolide and 3-methyl- and 2-methyl-3-propanolide all undergo predominantly the O-alkyl bond fission to give mixed anhydrides of β-chloropropionic acid. The reaction was postulated to proceed via dichloraluminum β-chloropropionate.
Intermolecular interaction between nitrophenols, such as m-, p-nitrophenol, 2,4-dinitrophenol, and picric acid, and adenine derivatives, such as N(6)-benzoyladenine, N(6)-benzoyl-2-methylthioadenine, and N(6)-benzyladenine, was verified by the formation of the corresponding molecular compounds. On the basis of these results, condensation reactions of these adenine derivatives with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose were carried out in nitrophenols, which were used as the activating agents. They were proved to afford the corresponding nucleosides in good yields. In addition, a novel glycosyl rearrangement reaction was first observed in the case of the reaction of N(6)-benzyladenine with the ribofuranosyl acylate.
The effect of pressure on the formolysis and methanolysis rates of representative secondary alkyl tosylates was investigated, and the activation volumes, ΔV0\
eweq, were estimated. The values of activation volume for formolysis were found to correlate excellently with σ*. This conformity of ΔV0\
eweq to the Hammett-type correlation is interpreted as a consequence of the kc-character of the reaction. The values of activation volume for methanolysis, however, converged to more negative values. The ks-character of methanolysis is thought to be responsible for this behavior. The kc-ks-hybrid nature of the reaction is also discussed.
Photochemical reduction of thiobenzophenone by 1,4-dihydrobenzene, 1,4-dihydronaphthalene, 9,10-dihydroanthracene, 1,3,5-cycloheptatriene, and acridane was studied. Relative reactivities and product analyses have revealed that the reaction is initiated by hydrogen-abstraction (one-electron-transfer followed by a proton migration) with thiobenzophenone in the n,π* triplet state. Inability of diphenylmethane to undergo the reaction can be interpreted by means of this mechanism.
Studies were carried out on the hydride reduction of the following five stable N,S,S-tri(hetero)substituted carbonium ions: N,N,S,S′-tetramethyldithiocarbamidium ion (1a), 2-dimethylamino-1,3-dithiolanylium ion (1b), 2-dimethylamino-1,3-dithianylium ion (1c), 2-methylthio-3-methyl-4,5-dihydrothiazolium ion (1d), and 2,3,5,6-tetrahydrothiazolo[2,3-b]thiazolium ion (1e). Sodium dihydrobis(methoxyethoxy)aluminate (RDB) was found to be a suitable reducing agent. The RDB reduction of the carbonium ions at −5 °C gave the corresponding formamide thioacetals (2) in moderate yields. This provides a practical method for the synthesis of formamide thioacetals. The RDB reduction of 1d at higher temperature, however, yielded abnormal products, thiazolin-2-thione (3) and thiazolidine (4) instead of the formamide thioacetal (2d). The mechanism for the formation of 3 and 4 has been discussed in terms of the ambident character of the cation (1d). Pyrolytic reactions of the thioacetals (2) and unsuccessful attempts to abstract the methine proton of 2b by various bases are also described.
A general synthetic route to unsymmetric 3,6-dialkylidene and 3-alkylidene-6-arylidene-2,5-piperazinediones is described. The condensation reaction of ethyl 2-oxocarboxylates with chloroacetamide in the presence of several acidic catalysts afforded N-chloroacetyldehydroamino acid esters. These compounds were cyclized in saturated ethanolic ammonia to give 3-monoalkylidene and benzylidene-2,5-piperazinediones (2). Compound 2 and 1-monoacetyl- or 1,4-diacetyl-3-alkylidene and benzylidene-2,5-piperazinediones, derived from a reaction of 2 with acetic anhydride, were condensed with alkyl and arylaldehyde in the presence of bases to afford 5.
The one-electron reduction of a series of phenyl- and/or n-propyl-substituted cyclopropenium ions with Cr(II) has been carried out in a 10% HCl solution. The reduction of triphenylcyclopropenium (Ia), diphenyl-n-propylcyclopropenium (Ib), and phenyldi-n-propylcyclopropenium (Ic) ions quantitatively gives dimers of the respective cyclopropenyl radicals, i.e., the bis(cyclopropenyl) derivatives, whereas the tri-n-propylcyclopropenium ion (Id) is quite unreactive. A kinetic study has shown that the reactivity of these stable carbonium ions toward the one-electron reductant (Cr(II)) is lowered with a decrease in the number of the phenyl substituent: k225°C=3.0×10−4l/g-ion·s for Ia, 2.7×10−6l/g-ion·s for Ib, 2.8×10−9l/g-ion·s for Ic, and <10−11l/g-ion·s for Id. The added NaCl was found to accelerate the reduction rate of Ia, whereas the added HCl showed an initial rate enhancement effect, followed by a slight rate-retarding effect. A plot of logk2 against the electron affinities of the respective cations, estimated from the transition energies of the charge-transfer bands for Ia,b with pyrene, has been found to fit a linear correlation previously obtained for a series of tropylium ions. The values of logk2 also exhibit a linear free-energy relationship with the pKR+ of these cations.