AN EXPERIMENTAL AND THEORETICAL-STUDY ON STEREOSELECTIVE ADDITION TO 3-FORMYL-DELTA-2-ISOXAZOLINES .1. 1,3-ANTI-SELECTIVITY INDUCED BY BF3OET2

Experimental and theoretical investigations of the anti-selective nucl eophilic addition induced by BF3 to 3-formyl-DELTA2-isoxazolines are d escribed. Ab initio molecular orbital (MO) calculations show that the 3-formyl-DELTA2-isoxazoline-BF3 complex prefers s-trans conformation t o s-cis conformation. Nucleophiles attack the stable s-trans conformer from the opposite side of C(4) substituent, giving anti-adducts selec tively. The B-O bond lengths and the stabilization energies suggest th at the features of the complex resemble those of aliphatic aldehyde-BF 3 complexes. Introduction of substituent to allyl tin improves the ant i-selectivity from 87/13 to 98/2. These results suggest that the react ion proceeds via anti-periplanar transition state.