Highly regio- and stereoselective asymmetric bromoazidation of chiral α,β-unsaturated carboxylic acid derivatives:: Scope and limitations

[GRAPHICS] Lewis acid catalyzed asymmetric bromoazidation of chiral alpha,beta-unsaturated carboxylic acid derivatives was performed using N-bromosuccinimide (NBS) and trimethylsilyl azide (TMSN3) as the bromine and azide sources. Among the Lewis acids, Yb(OTf)(3) was found to be the best catalyst. Regio- and anti-selectivity of 100% and moderate to good diastereoselectivity (up to 89:11) with good yields were obtained when Oppolzer's bornane sultam chiral auxilairy was used. Diastereoselectivity of > 95:05 was observed when (2S, 5S)-2,5-diphenylpyrrolidine was used as the chiral auxiliary.