ENANTIOCONTROL IN INTRAMOLECULAR CYCLOPROPANATION OF DIAZOKETONES - CONFORMATIONAL CONTROL OF METAL CARBENE ALIGNMENT

Diazo ketones with gamma or delta double bonds undergo catalytic intra molecular cyclopropanation. These reactions occur with high enantiocon trol when catalyzed by copper semicorrins and bis-oxazolines, but low enantiocontrol characterizes reactions catalyzed by a broad selection of chiral dirhodium(II) carboxamidates. The reverse stereocontrol occu rs for intramolecular cyclopropanation of allylic and homoallylic diaz oacetates and diazoacetamides. This divergence is explained by conform ational control of carbonyl alignment (syn or anti to the metal) of th e metal carbene intermediate.