Reactions of p-ylides with sulphenes

Abstract

The reactions of stable P-ylides with sulphonyl chlorides in the presence of triethylamine have been investigated. P-Ylides bearing an c~-hydrogen such as carbethoxymethylene- and benzoylmethylene-triphenylphosphoranes react with methanesulphonyl chloride to yield c~- sulphonated P-ylides (A). On the other hand, if P-ylides having no s-hydrogen are used, episulphones (B) or their decomposition compounds, olefins (C), and (alkanesulphonyl)methylene P-ylides (the sulphene insertion compounds) (D), are obtained. The ratio of B and D is 4:1 in the reaction with fluorenylidenetriphenylphosphorane, but D is usually the principal product in the reaction with a series of ~-carboalkoxy(or carbophenoxy)ethylidenetriphenylphosphoranes. ALTHOUGH the successful isolation of sulphenes has not been achieved, their transitory existence has been indicated in many reactions in which both sulphonyl halides and tertiary amines are involved. For example, in reactions with electron-rich olefins such as enamines, ketene acetals, or ketene aminals, the formation of four-membered ring sulphones (thiethane dioxides) could be understood as a result of cycloadditions of sulphenes to these olefins. 1 Moreover, recently two research groups have independently obtained strong evidence for intermediate sulphenes in the base-catalysed solvolysis of sulphonyl chlorides, namely through the appearance of nearly one and only one atom H--D exchange at the ~-position to the sulphonyl group during the reaction in deuterated media. 2 An electrophilic attack of halocarbenes (generated in situ) on P-ylides leading to halo-51efins has been described. 3~,b'° We now wish to report the results on an analogous reaction between sulphonyl chlorides, which would act as sulphene sources in basic media, and stable P-ylides. Treatment of stable P-ylides bearing an e-hydrogen such as carbethoxymethylene- and benzoylmethylene-triphenylphosphoranes with methanesulphonyl chloride and triethylamine afforded ~-sulphonyl P-ylides in which the e-hydrogen had been replaced by methanesulphonyl group. This sulphonation is similar to e-acylation of stable P-ylides with acyl halides. 4 A priori, two reasonable reaction paths can explain this sulphonation: (1) an electrophilic addition of sulphene initially formed to the