The synthesis of pyrroles from N-alkenylisoxazol-5(2H)-ones

Abstract

Isoxazol-5(2H)-ones undergo Michael addition to propiolate esters under mildly basic conditions to form N-alkenylisoxazolones, with small amounts of the isomeric G or O-alkylated materials. The former lose carbon dioxide when subjected to flash vacuum pyrolysis or photolysis, and give pyrroles in ca 40% yields. Minor accompanying products arise from capture of the intermediate carbene by solvent, or from hydrogen atom abstraction.