The generation and the reaction of beta-copper(II) ketones via electrophilic ring opening of siloxycyclopropanes with copper(II) tetrafluoroborate (Cu(BF4)2) were studied. Treatment of siloxycyclopropane with Cu(BF4)2 resulted in desilylative dimerization to give a 1,6-diketone in good yield. The ring opening took place regioselectively across the bond between the methylene and siloxy carbons. The reaction is reasonably interpreted by assuming the electrophilic ring opening by cupric ion to form beta-copper(II) ketone and trimethylsilylfluoride, followed by dimerization. With dimethyl acetylene dicarboxylate (DMAD) and water, beta-(acyl)alkyls were captured to give dimethyl 2-(3-oxoalkyl)maleate with high degree of stereoselectivity. The stereoselective transfer of beta-(acyl)alkyl arises from syn addition across the triple bond followed by in situ protonation of the resulting vinylcopper species with retention of configuration. The stereoselective transfer of beta-(acyl)alkyls to acetylenic sulfones, which gives beta-(acyl)alkylated vinylic sulfones, was also successful.