Dimethyloxosulphonium methylide

Phase-transfer catalytic conditions provide an extremely powerful alternative to the use of alkali metal hydrides for the synthesis of cyclopropanes via the reaction of dimethyloxosulphonium methylides with electron-deficient alkenes [e.g. 54-56] reaction rates are increased ca. 20-fold, while retaining high yields (86-95%). Dimethylphenacylsulphonium bromide reacts in an analogous manner with vinyl-sulphones [57] and with chalcones [58] and trimethylsulphonium iodide reacts with Schiff bases and hydrazones producing aziridines [59]. 

The intermediacy of oxaspiropentanes was first proposed in some reactions i.e. the addition of diazomethane to cyclohexanone the reaction of dimethyloxosulphonium methylide with a-haloketones and the reaction of iV,iV-dimethylaminophenyloxo-sulphonium cyclopropylide with ketones . The parent oxaspiropentane (115) has been obtained from the p-nitroperbenzoic acid oxidation of a methylene chloride solution of methylenecyclopropane (69) at - 10°C (equation 82). ... 

The 3,6-cyclo-A-nor-3,5-secoandrostanes (354) were synthesized through reduction of the enol lactones (355) (see ref. 67). The syntheses of 5,7/3-cyclo-B-homo-5/3- and 6/S,7a/S-cyclo-B-homo-5a-cholest-2-enes and derivatives of these were reported.Notably, reaction of the 6j8,7a/3-cyclo-B-homo-compound (356) with HOBr and with peracid gave, in each case, a single product resulting from exclusive -face attack.Methylenation of cholesta-4,6-dien-3-one with dimethyloxosulphonium methylide gave 6/8,7aj8-cyclo-B-homocholest-4-en-3-one and the 6a,7a-epimer. ... 

An interesting variation in the stereochemistry of addition of dimethyloxosulphonium methylide to 5-acetylpyrrolidin-2-one is produced by the addition of anhydrous ZnCl282. In the absence of the salt a 78 22 mixture of epoxides (47 a-Me) and (47 -Me) results, whereas, with added ZnCl2, this ratio changes to 23 77-... 

Full details have appeared of the synthesis of thiabenzene 1-oxides from the reaction of acetylenic ketones with dimethyloxosulphonium methylide (Scheme 1), following a preliminary account. By working at low temperatures with THF-DMSO solutions, intermediate allylides (22)—(24) could... 

Four-membered Rings.— This Section will include examples of /3-lactam synthesis since these molecules serve as interesting intermediates for the preparation of antibiotics, both natural and synthetic, and as fascinating molecules in their own right. Methylene transfer for conversion of aziridines into azetidines has been little explored. The reaction of dimethyloxosulphonium methylide with... 

Reactions.—A variety of examples have appeared of oxiran and cyclopropane formation through addition of dimethyloxosulphonium methylide to carbonyl compounds and to conjugated double bonds, respectively. The mechanism of this latter process has been investigated. Synthetic applications of cycloalkenone 3-dimethyloxosulphonium methylides have been explored, providing the basis in one case for a novel approach to hydroazulenes (22). 

An unusual 1,4-oxathian synthesis, the formation of (174) in 12% yield, was observed in the phase-transfer-catalysed generation of dimethyloxosulphonium methylide and its reaction with benzaldehyde. A possible pathway to (174) involves protonation and dehydration of the initial ylide-benzaldehyde adduct to give (175). Ylide formation at a methyl... 

A variant of the dimethyloxosulphonium methylide synthesis of thiaben-zene 1-oxides has been developed in which 2,2-diacyl-1-alkoxyethylenes (21) are used in place of aj3-ethynyl ketones (Scheme 1). The thiabenzene 1-oxides (22)—(24) were obtained directly, but the stable intermediate (25) was isolated in the synthesis of the derivative (26) using diethyl ethoxy-methylenemalonate. The H-2 and H-6 signals in the H n.m.r. spectra of compounds (22)—(24) and (26) occur at relatively high field (H-2,... 

A further example has been reported of the formation of a benzene derivative (44) from the 2,4,6-triphenylthiopyrylium cation and a reactive carbanion, in this case dimethyloxosulphonium methylide. 

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