Computational educidation of the catalytic mechanism for ketone reduction by an oxazaborolidine-borane adduct

The reaction pathway around the complete catalytic cycle for THF-borane reduction of propanone catalysed by the oxazaborolidine form (S)-proline has been determined by AM1 semiepirical MO calculations, including characterisation of all transition structures; the transition structure for ketone coordination is almost as high in energy as that for the rate-limiting hydride-transfer step, and the calculated kinetic isotope effect for reduction by THF-[ ²H₃]borane is in accord with experiment.