Identification of Reactive Intermediates for the Decarbonylative Reaction of 1-Alkylprolines

1-Alkylprolines undergo decarbonylative reactions with oxalyl chloride and subsequent Mannich reactions with nonactivated C-H nucleophiles to give 2-substituted pyrrolidines as Mannich adducts. We showed that 1-alkyl-1-pyrrolinium compounds are the reactive intermediates formed by the decarbonylative reactions of 1-alkylprolines. Our results also confirmed that an azomethine ylide, although unreactive toward the Mannich reaction and not involved in the decarbonylative Mannich reaction, can be generated by deprotonation of the corresponding 1-alkyl-1-pyrrolinium compound under mild conditions.