Diastereoselection and diastereofacial selection in 5-(3,4) ene cyclizations: Recent studies and applications in organic synthesis

Abstract

Stereoselectivities in the thermal and Lewis acid-catalysed 5-(3,4) ene cyclizations of 1.6-dienes activated by one or two electron- withdrawing groups on the enophile are studied. Inadequacy of HouK's force field model to explain the preponderance of trans products is discussed. High diastereoface selectivity is observed in ene cyclizations of 1,6-dienes carrirng a silyloxy group in the tether. The ene adducts with a strategically placed trimethylsilyl group in the olefinic side chain are of value as exemplified by the synthesis of (+-)-hirsutene and (+-)-methyl cucurbate.