Stereoselective C-4 functionalisation of flavan-3-ols. The significance of conformational mobility of the flavan heterocycle in stereoselectivity at the benzylic carbon

Abstract

The peracetates of (+)-catechin [(2R,3S)-2,3-trans-3′,4′,5,7-tetrahydroxyflavan-3-ol] and a variety of related flavan-3-ols are very susceptible to formation of their 4β-bromo derivatives when treated with NBS in the presence of benzoyl peroxide. The observed stereospecific C-4-brominations, and the stereoselectivity displayed during substitution reactions of the functionalised flavan-3-ols, are explicable in terms of conformational mobility of the flavan heterocyclic ring.