Tin—Copper Transmetalation: Cross-Coupling of α-Heteroatom-Substituted Alkyltributylstannanes with Organohalides

Copper (I), in the absence of other transition metals, catalyzes the cross-coupling of (α- (acyloxy)benzyl)- tributylstannanes with allylic bromides in THF in fair to good yields and with aryl/vinyl halides less efficiently or not at all. Simple (α- (acyloxy)alkyl)tributylstannanes react sluggishly even with allyl bromide. However, proximal thiosubstituents on either reaction partner dramatically enhance yields, reaction rates, and the variety of suitable educts. (α-Phthalimidoylalkyl)tributylstannanes afford protected α-amino thio esters. In contrast with the Stille reaction, copper-mediated cross-couplings of α-heteroatom-substituted alkyltributylstannanes proceed with complete retention of configuration via a coordinatively stabilized organocopper intermediate that can be intercepted in good yield by 1, 4-conjugate addition to 2-cyclohexen-1-one.