The first copper-catalyzed formal carboboration of alkynes, in which a C-B bond and a C-C bond are created in a single catalytic cycle, is presented. The reaction proceeds with high regioselectivity and syn-stereoselectivity to form tri- and tetrasubstituted vinylboronic esters from commercially available bis-(pinacolato)diboron. A subsequent cross-coupling reaction gives access to highly substituted alkenes.