The Stereochemistry of Carbenoid Cyclopropanation Reactions

The stereochemical course of the intramolecular carbenoid cyclopropanation reaction has been studied for the epimeric carbenoids 12a and 12b. In these reactions the tert‐butyldimethylsilyloxy substituent serves as an internal stereochemical reference point. It was found that 12b cyclizes rapidly at −110°C in a complexation‐assisted concerted process to give the bicyclo[3.1.0]hexane 16. The diastereomer 12a cyclizes more slowly at −100°C to give both 16 and 17; the former is probably formed by a complexation‐assisted carbolithiation pathway.