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)