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

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.