A Cross Metathesis Based Protocol for the Effective Synthesis of Function­alised Allyl Bromides and Chlorides

Abstract

Functionalised allyl halides, useful starting materials for the preparation of substituted organometallic reagents can be simply obtained by a straightforward approach. Hoveyda's ruthenium carbene catalyst 3, used in catalytic amount (2 mol%), is able to promote the cross metathesis of allyl bromide and chloride with a variety of different substituted olefins giving the corresponding functionalised allyl halides in satisfactory yields. trans-Olefins are obtained as major diastereoisomers reaching 90:10 (trans:cis) ratio when allyl chloride is used as the metathesis partner. This reaction represents a simple and accessible way for the preparation of valuable precursors for functionalised organometallic reagents. In particular, the use of functionalised allyl bromides (lOb and 13) in the enantioselective Nozaki-Hiyama reaction promoted by [Cr(Salen)Cl] is presented.