Stereoselective Synthesis of Trisubstituted Vinyl Bromides by Addition of Alkynes to Oxocarbenium Ions

Abstract

We have developed an efficient method for the synthesis of trisubstituted (E)-vinyl bromides by a Friedel–Crafts-type addition of alkynes to oxocarbenium ions formed in situ from acetals. The success of this reaction relies on the identification of magnesium bromide etherate as both a Lewis-acid promoter and a source of bromide. This reaction employs simple inexpensive starting materials and proceeds under mild conditions to allow the preparation of a range of vinyl bromide products in high yields and high E/Z selectivities. Furthermore, the vinyl bromides also contain an allylic ether functional group. Both the vinyl bromide and allylic ether groups are effective handles for the elaboration of these useful synthetic intermediates.

Key words

haloalkenes - stereoselectivity - oxocarbenium ions - ­Friedel–Crafts reactions - alkynes - vinylations

• References and Notes

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