Catalytic Asymmetric Intramolecular Cyclopropanation of α-Diazo-α-Silyl Acetate

The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of α-diazo-α-silyl acetates to form oxabicyclo[3.2.1]hexane, which proceeds with high yields and enantioselectivities, is described. The maximum enantiomeric excess observed was 96% ee and the absolute configuration of the products was elucidated. The counteranion of the Cu(I) catalyst was found to play a crucial role in determining the yields and enantioselectivities, with highly anionic counteranions improving both yields and enantioselectivities. Our previously reported model explains the enantiofacial selectivity of the reacting alkene.