Samarium Diiodide Induced Reactions of Cyclopropyl Ketones: Reductive Ring Cleavage and Dimerization Leading to 1,8‐Diketones – Scope, Limitations, Mechanisms

Reactions of the samarium diiodide/HMPA complex with alkyl cyclopropyl ketones such as 3, 5, and 7 provided dimers incorporating a 1,8‐diketone moiety. The products 4, 6, and 8 were isolated in moderate to good yields. The aryl‐substituted cyclopropyl ketones afforded a broader product spectrum, which results from the attack of samarium intermediates to the aryl group. Cyclopropyl phenyl ketone (13) gave dimer 14, where one cyclopropane ring was reductively cleaved, whereas the second one is still present. The reductive dimerization of cyclopropyl 2‐thienyl ketone (21) furnished the product 22, which still contains two cyclopropyl groups. Further examples demonstrate the diversity of samarium diiodide induced reductions of cyclopropyl ketones. Plausible reaction mechanisms involving samarium ketyl intermediates are presented.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)