Quantum chemical study on enantioselective reduction of aromatic ketones catalyzed by chiral cyclic sulfur-containing oxazaborolidines. Part 3. Structures of catalyst-alkoxyborane adducts

Abstract

The chiral cyclic sulfur-containing oxazaborolidine catalyst reacts with aromatic ketone in the presence of borane to form the catalyst–alkoxyborane adduct with a B-O-B-N four-membered ring. The ab initio molecular orbital method is employed to study the structures of the catalyst–alkoxyborane adduct. All the calculated systems are optimized completely by means of the Hartree–Fock method at 6-31g* basis sets. The B-O-B-N four-membered ring is stable, although there is strong tensile stress in the four-membered ring. The catalyst–alkoxyborane adduct exists in four stable structures. Among these structures, the largest energy difference is only about 4 kJ/mol. In the catalyst–alkoxyborane adduct, the B(2)N(3) bond in the catalyst is weakened greatly. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 261–268, 2000