A copper-catalyzed C(sp(3))-Si cross-coupling of aliphatic C(sp(3))-I electrophiles using a Si-B reagent as the silicon pronucleophile is reported. The reaction involves an alkyl radical intermediate that also engages in 5-exo-trig ring closures onto pendant alkenes prior to the terminating C(sp(3))-Si bond formation. Several Ueno-Stork-type precursors cyclized with excellent diastereocontrol in good yields. The base-mediated release of the silicon nudeophile and the copper-catalyzed radical process are analyzed by quantum-chemical calculations, leading to a full mechanistic picture.