Ketenimines bearing electron-withdrawing groups (X in 1) at the C2-position react with lithium trimethylsilyldiazomethanide [diazo(lithio) trimethylsilylmethane] to give 4-amino-3-trimethylsilylpyrazoles 4 or 5 mainly; in some cases 4-trimethylsilyl-1,2,3-triazole derivatives 3 were formed as the major products.
N-Ethyl(diethylphosphono)methylketen imine, a new type of keten imine, was easily prepared in high yield, and reacted with the sodium salts of salicylaldehyde and 2-formylpyrrole to afford the benzopyran and pyrrolizine derivatives, respectively.