A copper-catalyzed ring-opening diborylation of vinylcyclopropanes has been developed, providing efficient access to stereodefined 1,5-diborylalkenes from readily accessible substrates. In the presence of a dcpe-ligated copper catalyst and bis(pinacolato)diboron (B2pin2), a broad range of 2-aryl vinylcyclopropanes undergo selective C−C bond cleavage and diborylation under mild conditions, affording trisubstituted alkenyl diboronates in moderate to high yields with high regio- and stereoselectivity. The alkenyl boronate products contain both allylic and homoallylic boronate functionalities and can undergo sequential and selective transformations to furnish a variety of functionalized compounds. Mechanistic studies reveal that NaBHEt3 activates CuI/dcpe to generate a copper hydride species, which enters the catalytic cycle by reacting with B2pin2 to form a catalytically competent copper−boryl intermediate. This copper-catalyzed ring-opening diborylation proceeds through borylcupration of the vinylcyclopropane followed by β-carbon elimination and turnover via B2pin2.
Tan et al. (Mon,) studied this question.