Stereoselective synthesis of (Z/E)-1,2-dibromoalkenes from terminal alkynes

Abstract

A Ag–CH₃SO₃H co-catalyzed direct Z-selective synthesis of 1,2-cis-dibromoalkenes from alkynes has been developed. Mechanistic studies showed that the reaction proceeded through the formation of a silver allene cation intermediate followed by sequential bromine free radical addition and substitution. This discovery might open up a new arena for silver catalysis and important allene chemistry. Additionally, an efficient PPh₃-promoted E-selective synthesis of 1,2-trans-dibromoalkenes from alkynes is also disclosed. Both protocols utilized the easy-to-handle N-bromosuccinimide as the sole brominating reagent and proceeded under much milder reaction conditions.