3-Hydroxypyrroles and 1H-pyrrol-3(2H)-ones. Part 2. Scope and limitations of the synthesis of pyrrol-3-ones by pyrolysis of aminomethylene Meldrum's acid derivatives

Abstract

Flash vacuum pyrolysis of N,N-disubstituted aminomethylene Meldrum's acid derivatives provides a route to 4,5-unsubstituted 1H-pyrrol-3(2H)-ones by a hydrogen-transfer–cyclisation sequence. Alkyl and aryl 1-substituted, 1,2-disubstituted, and 1,2,2-trisubstituted pyrrolones can be obtained. In competitive cases, there is little selectivity between hydrogen transfer from primary, secondary, or tertiary sites, although benzyl hydrogen atoms proved particularly reactive, giving a general synthesis of 2-phenyl-1H-pyrrol-3(2H)-ones.