A Boron-Oxygen Transborylation Strategy for the Asymmetric Reduction of Ketones

Abstract

The asymmetric reduction of ketones with pinacolborane (HBpin) has been catalysed by an enantioenriched borane catalyst, formed <i>in situ</i> from 9-borabicyclo[3.3.1]nonane (H-<i>B</i>-9-BBN) and β-pinene. While previously only used stoichiometrically, this borane has now been rendered catalytic using a new turnover mechanism, B-O transborylation. Thermodynamic and kinetic parameters of the key B-O/B-H transborylation showed this is a sub-class of σ-bond metathesis.