Synthesis of condensed tannins. Part 4. A direct biomimetic approach to [4,6]- and[4,8]-biflavanoids

摘要: The generation of flavanyl-4-carbo-cations from flavan-3,4-diols and their condensation with nucleophilic flavan-3-ols to form [4,6]- [4,8]-biflavanoids at ambient temperatures under mildly acidic aqueous conditions apparently simulates the initial step in condensed tannin formation a number natural sources. stereospecificity (or stereoselectivity) reaction is conditioned mainly by 2,3-cis or 2,3-trans stereochemistry parent flavan-3,4-diol, but also nucleophilicity flavan-3-ol, its regiospecific regioselective) course steric factors arising variation substitution receptive A-ring flavan-3-ol.