Catalytic Asymmetric Addition of Grignard Reagents to Alkenyl-substituted Aromatic N-heterocycles

Catalytic asymmetric conjugate addition reactions represent a powerful strategy to access chiral molecules in contemporary organic synthesis. However, their applicability to conjugated alkenyl-N-heteroaromatic compounds, of particular interest in medicinal chemistry, has lagged behind applications to other substrates. We report a highly enantioselective and chemoselective catalytic transformation of a wide range of β-substituted conjugated alkenyl-N-heteroaromatics to their corresponding chiral alkylated products. This operationally simple methodology can introduce linear, branched, and cyclic alkyl chains, as well as a phenyl group, at the β-carbon position. The key to this success was enhancement of the reactivity of alkenyl-heteroaromatic substrates via Lewis acid activation, in combination with the use of readily available and highly reactive Grignard reagents and a copper catalyst coordinated by a chiral chelating diphosphine ligand.