A COMPUTATIONAL STUDY ON THE ACTIVATION OF CHIRAL N-SULPHONYLATED OXAZABOROLIDINONES BY LEWIS-ACIDS

Activation of N-sulphonylated oxazaborolidin-5-ones as Lewis acids cap able of binding aldehydes was studied computationally by means of ab i nitio methods. Formaldehyde was used as a model of aldehydes and N-sul phonyl-1,3,2-oxazaborolidin-5-one 1' as a model of the oxazaborolidino nes. Energies (RHF/MP2/6-31G//RHF/MP2/6-31G*) of the coordination of H2C=O to 1' were -42 kJ mol(-1) (H2C=O as a monodentate ligand) and -2 5 kJ mol(-1) (H2C=O as a bidentate ligand) when 1' was activated (by c oordination of borane to O-SC=0 of the oxazaborolidin-5-one moiety). T he corresponding energies were -23 and -4 kJ mol(-1) in the case of no n-activated 1'. Results of this study support the existence of novel C -H- -O hydrogen bonds proposed by Corey et al. but indicate that the b onds can be based on electrostatic interactions only. Energies of the novel bonds were estimated to be about 10 kJ mol(-1) (as calculated in CH2Cl2). (C) 1997 Elsevier Science Ltd.