Highly Regio- and Stereoselective Asymmetric Bromoazidation of Chiral α,β-Unsaturated Carboxylic Acid Derivatives: Scope and Limitations

Abstract

Lewis acid catalyzed asymmetric bromoazidation of chiral α,β-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.