NMR investigations on boron complexes in the conjugate addition on alpha,beta-unsaturated imides.

[reaction: see text]. The 1,4-addition of O-benzylhydroxylamine to alpha,beta-unsaturated imide 1 in the presence of BF3.Et2O proceeds with the preferential attack of the nucleophile on the Cbeta-re face. To explain this unexpected reactivity 1H, 13C, and 11B NMR investigations have been carried out on the boron-imide complex, which show the presence of an S-cis imide chain conformation.