Sulphenyl ketones

For example, several microorganisms have been employed for the reduction of a,a,a,-trifluoromethyl a -sulphenyl ketones (Fig. 15-33). Some of them produce the corresponding alcohols in high diastereo- and enantioselectivities the high conver-... 

Figure 15-33. Reduction of sulphenyl ketones followed by epoxide formation I,82l.

Enethiols are reactive molecules and therefore useful starting materials in syntheses. They are acyl anion equivalents and good Michael acceptors. Addition of a thiol to the double bond, followed by Horner-Wittig reaction and then hydrolysis, constitutes a regioselective synthesis of a-sulphenyl ketones (equation 97). 

Oxirans.—A new general synthesis of oxirans from a-sulphenylated ketones has been described (Scheme 1) the procedure leads exclusively to ci5-epoxides... 

Unfortunately, the usual routes to a-PhS ketones 94, from the parent ketone33 6i, 62) by sulphenylation or halogenation, themselves require a solution of the specific enol problem This can be found if silyl enol ethers are combined with PhSCl63). 

A series of cyclic 1,2-diketones have been prepared via the a-methylthioketbnes prepared by sulphenylation of the ketone enolate with dimethyl disulphide, by treatment with a mixture of copper(II) chloride and copper(II) oxide in aqueous acetone... 

In a study of sulphenylations and dehydrosulphenylations of esters and ketones it has been reported that quenching the enolate of (507) with dimethyl disulphide or diphenyl disulphide affords (508 R = Me or Ph). Oxidation with sodium... 

The characteristic reaction behaviour of sulphenyl halides is exemplified in a wide range of alkyl- or aryl-thiolation processes. 2,3-Dimethylindole gives (153) with 2,4-dinitrophenylsulphenyl chloride, and a-phenyl-thiolation of ketones (PhSCl + Ri CO CHR R R -CO-CR R SPh) ... 

T. S. Croft, Phosphorus Sulfur, 1976, 2, 133 [phenols -1- CF3SCI - ortho- and para-substitution products) Yu. V. Zeifman, L. T. Lantseva, and I. L. Knunyants, Izv. Akad. Nauk SSSR, Ser. Khim., 1978,1229 and K. Hiroi, Y. Matsuda, and S. Sato, Chem. Pharm. Bull., 1979,27,2338 [sulphenylation of ketone anions and 1,3-dicarbonyl dianions, respectively see also A. De Groot and... 

Arylsulphenylation of 1,3-dicarbonyl compounds cm be effected at room temperature in an Et4N+ F" emulsion, but dianions R CHCOCHCOR, formed by successive treatment with NaH and Bu"Li, are sulphenylated at the alternative site by RbSSPh. 8-Keto-esters, malonates, and a-cyanoalkanoates can be sulphenylated and decarbalkoxylated in a one-pot process by reaction at 150—160 C, in HMPA, with PhSSPh and Nal, providing a-(phenylthio)alkyl ketones, cp(phenylthio)alkanoates, and tf-cyanoalkyl phenyl sulphides. 

Another example of the addition of sulphur-stabilized carbanions to carbonyl groups is shown in the synthesis of a-sulphenylated aldehydes (179) from ketones (RR CO) and PhSCHOMe, and of vinyl sulphides or thioacetals from ketones and R C(SR)2 or C(SR)3, respectively. a-Sulphenylated aldehydes are also formed by electrolysis of vinyl sulphides as in the conversion of PhC=CSR to PhCH(SR )CHO. The carbanion PhSCH2 adds specifically to the ketone in (180) to provide methylenecyclohexenes by further elaboration as shown in Scheme 33. °... 

Thio- and Seleno-ketones.—A new regiospecific synthesis of a-thioketones has been described (Scheme 1)." Note that desulphurization of a-phenylthioketones can be achieved by treatment of these ketones with zinc and chloro-trimethylsilane." Methyl 2-nitrophenyl disulphide is a convenient reagent for bis-a-sulphenylation of ketones."... 

When cyclohexanones are treated with diphenyl disulphide and sodium methoxide, aromatization accompanies sulphenylation if not more than one alkyl group is present in the a-position of the ketone [equation (21)]. ... 

Allylic thiocarbamates (145) are available from ketones by sequential condensation with vinyl-lithium species and dimethylthiocarbamoyl chloride followed by a [3,3] sigmatropic rearrangement. It has now been shown that these can be used as precursors to a,jS-unsaturated esters by bis-sulphenylation and mercury(ii)-promoted hydrolysis (Scheme 39). Only the B-isomers are produced when the final product (146) is unsubstituted i.e. = H) or carries an a-methyl... 

Trapping of the initially formed aluminium enolate from a,/8-unsaturated ketones and diethylaluminium cyanide, with chlorotrimethylsilane-pyridine yields the corresponding silylenol ethers (35), which can be alkylated or phenyl-sulphenylated (Scheme 22). ... 

Paterson I, Osborne S. Enol borinates in organic synthesis regioselective a-sulphenylation and a-selenylation of ketones. Synlett 1992 145 146. 

Sulphenylation with a sulphenamide occurs in the formation of sulphides from an JV-alkylthio-phthalimide or -succinimide with a Grignard reagent or an alkyl-Iithium compound, respectively, and in the formation of a-phenylthio-ketones from enamines and (PhSlsN. ... 

Methods for the introduction of an a-alkylthio-group into an aliphatic ketone have been established, involving either treatment of the silyl enol ether derived from the ketone with MeLi and a sulphenyl chloride, or a-carbanion formation from the ketone with the Li salt of a secondary amine, followed by treatment with a disulphide or a sulphenyl halide. ... 

The interaction of azobenzene-2-sulphenyl bromide and methyl alkyl ketones in aqueous ethanol yields benzothiazol-2-yl alkyl ketones (33), by way of intermediate sulphides. ... 

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