Asymmetric Imine Hydroboration Catalyzed by Chiral Diazaphospholenes

Abstract

AbstractThe first use of diazaphospholenes as chiral catalysts has been demonstrated with enantioselective imine hydroboration. A chiral diazaphospholene prepared in a simple three‐step synthesis from commercial materials has been shown to achieve the highest enantioselectivity for the hydroboration of alkyl imines with pinacolborane reported to date. Enantiomer ratios of up to 88:12 were obtained with low (2 mol %) catalyst loadings. Twenty examples of asymmetric reduction employing this main‐group catalysis protocol, including the synthesis of the pharmaceuticals ent‐rasagiline and fendiline, are shown.