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

Functionalized allyl halides, useful starting materials for the prepn. of substituted organometallic reagents can be simply obtained by a straightforward approach. Hoveyda's ruthenium carbene catalyst, used in catalytic amt. (2 mol%), is able to promote the cross metathesis of allyl bromide and chloride with a variety of different substituted olefins giving the corresponding functionalized 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 prepn. of valuable precursors for functionalized organometallic reagents. In particular, the use of functionalized allyl bromides in the enantioselective Nozaki-Hiyama reaction promoted by [Cr(Salen)Cl] is presented.