Journal of the American Chemical Society, Vol.117, No.22, 5973-5982, 1995
Tin-Copper Transmetalation - Cross-Coupling of Alpha-Heteroatom-Substituted Alkyltributylstannanes with Organohalides
Copper(I), in the absence of other transition metals, catalyzes the cross-coupling of (alpha-(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 (alpha-(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. (alpha-Phthalimidoylalkyl)tributylstannanes afford protected a-amino thio esters. In contrast with the Stille reaction, copper-mediated cross-couplings of alpha-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.