A cross metathesis based protocol for the effective synthesis of functionalised allyl bromides and chlorides

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 (10b and 13) in the enantio selective Nozaki-Hiyama reaction promoted by [Cr(Salen)Cl] is presented.