Substituted Cyclobutenes, Their Preparation, and Their Versatility in Synthesis

Cyclobutene compounds are interesting intermediates that have proven to be useful in organic synthesis. This review mainly deals with preparations and reactions of some cyclobutenes disubstituted at the allylic position. Several possibilities in the area of the thermal ring opening of these compounds into dienes are explored, and some features of the selectivity of addition reactions to cyclobutenes to afford tri‐ or tetrasubstituted cyclobutanes are also examined. When suitable leaving groups are present, these cyclobutanes can yield cyclopropanes stereospecifically through ring contraction or bicyclic compounds through intramolecular cyclization. Some applications to the synthesis of nucleoside analogues and of bicyclic compounds are pointed out. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)