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

Racemic vinylallenes are shown to be attractive substrates for catalytic multicomponent diastereo-, and enantioselective 1,6-conjugate addition of multifunctional allyl moieties to easily accessible α,β,γ,δ−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 α,β,γ,δ-unsaturated diester. By just one operation, a variety of vinylallenes were converted to products bearing a Z-trisubstituted alkenyl–B(pin) moiety, a vinyl group, a β,γ-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. A variety of chemoselective modifications involving the alkenyl–B(pin), 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. These studies foreshadow the use of vinylallenes as starting materials in a wide range of multicomponent reactions, those catalyzed by Cu–H or Cu–B(pin) complexes.