Synthesis of condensed tannins. Part 10. ‘Dioxane-linked’ profisetinidins

Abstract

Isolation of a natural 2,3-trans-3,4-trans:2′,3′-trans-3′,4′-cis-diastereoisomer of the hitherto unique [3,4′:3′,4]-O,O-linked bis-(2,3-trans-3,4-cis-3′,4′,7-trihydroxyflavan) from a common source, the heartwood of Acacia mearnsii, has prompted synthesis of their hexamethyl ethers by self-condensation of (+)-3′,4′,7-trimethoxy-2,3-trans-flavan-3,4-trans-diol with BF₃–diethyl ether in dioxane. The major 3,4-cis:3′,4′-cis isomeric product of synthesis is subject to further condensation, and to inversion at a single C-2 chiral centre.

Simple and complex dibenzo-α-pyrones accompany the profisetinidins in a chromogenic fraction of the heartwood extract.