A novel synthesis of tricyclo[5.1.0.0(3,5)]octane-2,6-dione derivatives via double Michael addition-induced cyclopropanation reactions

Tricyclo[5.1.0.0(3,5)]octane-2,6-diones 1a-q were prepared in moderate yiel ds by the reaction of alpha,beta -unsaturated esters 2 with dihalomethane i n the presence of butyllithium, and by the reaction of dichloromethyl alpha ,beta -unsaturated ketones 3 with sodium ethoxide, respectively. This react ion was newly explained by a mechanism involving intermolecular double Mich ael additions of enolate anion 4 of ketones 3 and the following cyclopropan ation. (C) 2001 Elsevier Science Ltd. All rights reserved.