Mechanism and origin of stereoselectivity in Robinson annulations leading to bicyclo[3.3.1]nonanes: a rare Curtin–Hammet scenario

Abstract

Computational studies on the mechanism and diastereoselectivity of base catalyzed synthesis of bicyclo[3.3.1]nonanes by Robinson annulation are reported. Three possible mechanisms were considered, and only the methanol assisted H‐shift process could be the favorable pathway. We have discovered a rare Curtin–Hammet scenario: rate determining steps for the two diastereomeric products formed are completely different reactions, and a correction factor should be considered when gauging the ratio of products from competing pathways. The pathway leading to the anti product is kinetically preferred, which is consistent with experimental results. Finally, the ratio of the two products was rationalized. Copyright © 2016 John Wiley & Sons, Ltd.