Three-component coupling reactions of an alkyne, an enone, and a diboron reagent provide access to highly substituted alkenyl boronates in good to excellent yields (see scheme). The coupling is highly regio- and stereoselective, and the products are amenable to further functional-group transformations. R(1),R(2) = H, alkyl, aryl, CO(2)Me; R(3) = alkyl, Ph; R(4),R(5) = H, alkyl.