Formation of four-membered heterocycles

Robiette, Raphaël [UCL] Marchand-Brynaert, Jacqueline [UCL]

This review focuses on new developments in [2 þ 2] cycloadditions leading to four-membered heterocycles (b-lactams, b-lactones, b-sultams, azetidines, etc.) which appeared between 1992 and 2011. A special attention is drawn to the mechanistic aspects of the reactions and their consequences on the stereochemical outcome of the cycloaddition processes. Accordingly, the subdivision in sections reflects this point of view: the entries are related to reactions of various reagents (ketenes, enolates, ynolates, isocyanates, etc.) with CQX bonds instead of a list of types of heterocycles. The accent is also put on asymmetric catalysis, which is of particular interest for the enantioselective synthesis of biologically active compounds or their precursors.