3-Hydroxypyrroles and 1H-pyrrol-3(2H)-ones. Part 3. Pyrrolones from pyrolyses of aminomethylene Meldrum's acid derivatives: loss of chirality at the site of hydrogen transfer

Abstract

Pyrolyses of the diastereoisomeric Meldrum's acid derivatives (4) and (5), or of the chiral derivatives (6), (7), and (9), gives 2,2-disubstituted 1H-pyrrol-3(2H)-ones in which there is loss of configuration at the reaction site [e.g.(15) obtained from (9)]. The extent of configuration loss is greater if the reaction site is part of a ring. These results are explained by a two-step, hydrogen-transfer–cyclisation mechanism, following initial generation of a methyleneketene.