Mercaptals synthesis

Synthesis.— Thioketones (or enethiols) react with sulphur and carbon disulphide in DMF in the presence of triethylamine to give both 1,2-dithiole-3-thiones and l,3-dithiole-2-thiones thus heptane-4-thione yields 4-ethyl-5-propyl-l,2-dithiole-3-thione (1) and 4-ethyl-5-propyl-l,3-dithiole-2-thione (2). 5-Phenyl-4-styryl-l,2-dithiole-3-thione has been prepared by application of the well-known keten mercaptal synthesis, and some aryl-1,2-dithiole-3-thiones have been obtained, conventionally, by hi -temperature reactions of arylalkanes with sulphur. ... 

Addition of methyllithium to the lactone 1219, followed by reduction with sodium borohydride in refluxing ethanol, afforded, almost quantitatively, ellipticine (228). Reaction of the compound 1219 with the lithio derivative of formaldehyde diethylmercaptal, and reduction with sodium borohydride in refluxing ethanol, led to the mercaptal 1221. Cleavage of the mercaptal 1221 with bis(trifluoroacetoxy) iodobenzene [Phl(OCOCF3)2] in aqueous acetonitrile gave the 11-formyl derivative, which was reduced with sodium cyanoborohydride (NaBHsCN) to 12-hydroxyellipticine (232) (710,711) (Scheme 5.202). The same group also reported the synthesis of further pyiido[4,3-fc]carbazole derivatives by condensation of 2-substituted indoles with 3-acetylpyridine (712). 

As a result of these considerations, a rejuvenescence of interest in sulfonic esters of acyclic-sugar derivatives, e.g., of sugar mercaptals, is to be expected, since they afford a route to the synthesis not only of compounds having one or more methylene groups at desired positions in the sugar chain (of which 2-deoxy-D- ribose, or 2-deoxy-D-eryother groupings, e.g., double bonds, at selected positions in the chain. 

Schmidt and Wernicke74 have described a synthesis of digitalose starting with D-fucose dibenzyl mercaptal, which on condensation with acetone yielded the 4,5-isopropylidene derivative (LXXIV). Elimination of the dibenzyl mercaptal residues with mercuric chloride and cadmium carbonate in methanol gave 4,5-isopropylidene-D-fucose dimethylacetal (LXXV), from which the 2-benzyl ether was obtained on treatment with sodium and benzyl chloride. Methylation produced 2-benzyl-3-methyl-4,5-iso-propylidene-D-fucose dimethyl acetal (LXXVI), from which the iso-propylidene group was eliminated on treatment with methanolic hydrogen chloride, which also effected glycopyranoside formation (LXXVII). The... 

AUehyde synthesis. The carbanion generated from this reagent (I) reacts with an alkyl halide to give an aldehyde dimethyl mercaptal S-oxide (2). This product is easily... 

Micheel and Spruck improved the synthesis of a pentaacetyl-o-galactoseptanose by using 6-trityl-2,3,4,5-tetraacetyl-D-galactose diethyl mercaptal as the starting material. 

An alternative approach to the stereocontrolled synthesis of ulosonic acids was based on nucleophilic acylation of 2,3 5,6-di-O-isopropylidene-D-mannose 173 with a glyoxylate carboanion [116] derived from the mercaptal glyoxylate (Scheme 37). As a result the corresponding thio-octulosonates 174 and 175 were formed in 76% yield. Both compounds were converted to 176 using NIS (or NBS) and then MeONa. Applying Barton procedure [117] 176 was deoxygenated at C-3 to afford KDO derivative 124. 

S-Isopropyl-S-phenyl-N-tosylsulfilimine and a 5 mole excess of K-tert-butoxidc in benzene allowed to stand 15 hrs. at room temp, under isopropenyl phenyl sulfide. Y 80%. F. e. s. N. Furukawa, S. Oae, and T. Masuda, Chem. Ind. 1975, 396 with KOH in ert-butanol, prepn. of ketene mercaptals, s. H, Yoshida, T. Ogata, and S. Inokawa, Synthesis 1976, 552. 

Yinylketene mercaptals, diene synthesis with - 21, 728 suppl. 28 jS-Vinylketones... 

Benzaldehyde diethyl mercaptal added in one portion to a suspension of bis-(acetylacetonato)copper(II) and cupric chloride in dry tetrahydrofuran, stirred 8 hrs., and allowed to stand overnight at room temp. 3-(a-ethylthiobenzyl)-pentane-2,4-dione. Y 92% from acetylacetone in the presence of 2,6-lutidine as HCl-scavenger Y 79%. F. e. s. T. Mukaiyama et al.. Bull. Chem. Soc. Japan 43, 2549 (1970) sulfur compds. in synthetic organic diemistry, review, cf. L. Field, Synthesis 1972, 101. 

An alternate approach to the synthesis of polymercaptan precursor was considered by H. Ringsdorf et al. 28-31). They prepared vinyl mercaptals by either dehydration of the analc es S- -hydroxyethyl... 

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