Alkenic conjugate additions, organocuprates

The double bond can be restored after a conjugate addition to an electrophilic alkene if the enolate intermediate 110 is trapped as a silyl enol ether 111 and then combined with a sulfur or selenium electrophile which is later eliminated. Organocuprates are ideal nucleophiles for this process as the intermediate enolate can be trapped as a silyl enol ether and reacted directly with PhSCl or PhSeCl. 

PhotoadditioH of organohalides to alkenes. CuBr PBu is an effective catalyst for the regioselective photoinduced addition to electron-deficient alkenes. On reduction with zinc dust the overall result is the same as the conjugate addition using an organocuprate. However, in many cases this method is more convenient. 

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