New 3,3?[2,2?-oxy-bis-(oxazaborolidine)]-ethylenes. Structural studies by NMR, X-ray, and quantum chemistry methods

3,3?-[2,2?-Oxy-bis-(4S-methyl, 5R-phenyl-1,3,2-oxazaborolidine)]ethylene (4a) and 3,3?-[2, 2?-oxy-(4S-methyl-5R-phenyl-1,3,2-oxazaborolidine)- (1,3,2-benzoxazaborolidine)]ethylene (4b) were synthesized by the reaction of N,N?-bis-[(1R,2S)-norephedrine]oxalyl (3a) or N,N?-[((1R,2S)-norephedrine, o-hydroxyphenylamine]oxalyl (3b) with BH3-THF. The molecular structure of these compounds was established by NMR and infrared spectroscopy. The molecular geometry for 4 was studied by means of theoretical methods, resulting in structures that were in total agreement with those obtained by spectroscopy data and X-ray diffraction.