Z-Alkenylcuprates 1 and 2, prepared in situ by addition of acetylene to alkylcuprates, react with a variety of electrophiles (epoxides, carbon dioxide, aldehydes) and give conjugate addition products with a,ß-unsaturated aldehydes, ketones and esters, and with activated cyclopropanes. They also add across the triple bond of some alkynes. The synthesis of natural products (7,9,22) is described.