Racemic Vinylallenes in Catalytic Enantioselective Multicomponent Processes: Rapid Generation of Complexity through 1,6-Conjugate Additions

摘要

Racemic vinylallenes are shown to be effective substrates for catalytic multicomponent diastereo- and enantioselective 1,6-conjugate addition of multifunctional allyl moieties to easily accessible alpha,beta,gamma,delta-unsaturated diesters. Reactions may be catalyzed by 5.0 mol% of a readily accessible NHC-Cu complex at ambient temperature, and other than a vinylallene, involve B-2(pin)(2) and an alpha,beta,gamma,delta-unsaturated diester. A variety of vinylallenes were converted to products bearing a Z-trisubstituted alkenyl-B(pin) moiety, a vinyl group, a,beta,gamma-unsaturated diester unit, and vicinal stereogenic centers in up to 67% yield, 87:13 Z/E ratio, >98:2 d.r., and 98:2 e.r. Chemoselective modifications involving the alkenyl-B(pin), the vinyl, or the 1,2-disubstituted olefin moieties were carried out to demonstrate versatility and utility. Stereochemical models, based on mechanistic and DFT studies, demonstrate the dynamic behavior of intermediated Cu-allyl species and account for various selectivity profiles.