Copper(I)-catalyzed diastereoselective borylative exo-cyclization of alkenyl ketones with bis(pinacolato)diboron is reported. The reaction of alkenyl aryl ketones under a CuCl/Xantphos catalyst system provides four- or five-membered-ring syn-2-(borylmethyl)cycloalkanol derivatives in good yields with high syn selectivities. The utility of this method is demonstrated by further transformations of the cyclic products.