Asymmetric Imine Hydroboration Catalyzed by Chiral Diazaphospholenes
Matt R Adams1, Chieh-Hung Tien1, Robert McDonald2
1Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada.
Abstract:
The 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.
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