Novel base-catalysed rearrangements of (–)-fisetinidol-(+)-catechin profisetinidins with 2,3-trans-3,4-cis-flavan-3-ol constituent units

Abstract

The (–)-fisetinidol-(4β, 8)-(+)-catechin-O-methyl ether (1) is subject to facile C-ring isomerizations in NaHCO₃–Na₂CO₃ buffer solution to form a range of novel 8,9-cis-9,10-trans- and 8,9-trans-9,10-trans-3,4,9,10-tetrahydro-2H,8H-pyrano-[2,3-h]chromenes (2)–(5); analogues (4) and (5) are representative of an unique class of phlobatannins in which the resorcinol A- and pyrocatechol B-rings are interchanged.