Sulphonium and oxosulphonium carbalkoxymethylides

Sulphur-ylides with carbalkoxy substituent on the ylide carbon have been prepared and identified. They are classified into monoester type (IV, X), β-keto ester type (V, XII), malonamide ester type (VI, XIII), malonic diester type (XIV, XV) and lactone type (VIII). The structure of each class of compounds is discussed on the basis of IR and NMR spectra and large contribution of the betaine formula (A) is concluded. Reactions of less stable monoester type ylides IVa and X with trans-1,2-dibenzoylethylene resulted in formation of a cyclopropane XVIa and a cyclic sulphoxide XVII, respectively.