Synthesis of 2,3-Disubstituted Pyrroles Initiated by 1,4-Addition of Chelated Enolates onto Alkynyl Carbene Complexes

Chelated glycine ester enolates, which have been found to be good nucleophiles, e.g., for Michael additions, undergo 1,4-addtition toward alkynyl Fischer carbene complexes. Instead of the expected unsaturated carbene amino acid derivatives, 2,3-disubstituted pyrroles are formed, probably by a domino process initiated by the 1,4-addition. Subsequent 1,3-H-shift, 1,2-addition, and reductive elimination during workup finalized the reaction cascade.