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An investigation into the origins of the enantioselectivity observed in oxazaborolidine-catalyzed reductions of ketones was carried out by examination of the reaction surfaces generated using the MNDO Hamiltonian.The reports describing the enantioselective reduction of ketones using stoichiometric borane in the presence of catalytic amounts of chiral oxazaborolidines represent a significant advance in rational reagent design (Figure l).l These reactions presumably occur by the following sequence: (a) complexation of borane to the ring nitrogen; (b) coordination of the ketone oxygen to the ring boron; (c) hydrogen transfer from the NBH3-unit to the carbonyl carbon via a six-membered cyclic transition state. The (1) (a) Corey, E. J.; Bakshi, R. K.; Shibata, S . J. Am. Chem. SOC. 1987, 109,5551. (b) Corey, E. J.; Bakshi, R. K.; Shibata, S.; Chen, C.-P.; Singh, V. K. Sakurai, Y.; Ito, K.; Hirao, A.; Natmhrma, S. Bull. Chem. SOC. Jpn. 1987, 60, 395. (m) Rao, A. V. R.; Gurjar, M. K.; Shanna, P. A.; Kaiwar, V.

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