PPh3-catalyzed reactions of alkyl propiolates with N-tosylimines: a facile synthesis of alkyl 2-[aryl(tosylimino)methyl]acrylate and an insight into the reaction mechanism.

A new PPh(3)-catalyzed synthesis of alkyl 2-[aryl(tosylimino)methyl]acrylates from propiolate and N-tosylimine has been developed. Deuterium-labelling experiments show that the reaction mechanism involves several hydrogen-transfer processes, which are not the turnover-limiting step and strongly rely on the nature of the reaction media. The stable phosphonium-enamine zwitterion, which was proven to play an important role in the catalytic cycle, has been isolated and characterised by X-ray analysis.