Copper-Catalyzed Conjugate Additions of Alkylboranes to Imidazolyl α,β-Unsaturated Ketones: Formal Reductive Conjugate Addition of Terminal Alkenes

Conjugate addition of alkylboron compounds (allryl-9-BBN) to imidazol-2-yl alpha,beta-unsaturated ketones proceeded in the presence of a catalytic amount (10 mol %) of CuCl, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), and t-BuOK. The alkylboranes are available through alkene hydroboration, and thus the overall process represents a reductive conjugate addition of alkenes to enone derivatives. A variety of functional groups are tolerated in both the alkenes and the alpha,beta-unsaturated ketones. The 2-acylimidazole moiety can easily be converted into the corresponding carboxylic acid, ester, and amide derivatives.