Cyclo- and hydrodimerization of α,β-unsaturated ketones promoted by samarium diiodide

Abstract

Samarium(II) iodide is a strong one-electron transfer reducing agent, and is effective for the cyclo- and hydrodimerization of cyclic and non-cyclic α,β-unsaturated ketones. The title dimers can easily be prepared in good yields at room temperature under neutral conditions, using two-mole equivalent of SmI2 per mole of starting substrate. The reaction is stereocontrolled. The absence of an alcohol as a proton source is essential in the process and the use of HMPA as a copromoter improves the yield of dimeric products, making the reaction regioselective over the competitive CC double bond reduction. The crystal structures of some of the dimeric derivatives are reported. When η2- or η4-iron-coordinated α,β-unsaturated ketones are used as substrates, the reaction gives mainly the 1,4-reduced products.