Synthesis of a Condensed Tannin Model Compound, 4-(2,4,6-Trihydroxyphenyl)Flavan-3,3′,4′,5,7-Pentaol

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Abstract
A free phenolic condensed tannin model compound, 4-(2,4,6-trihydroxyphenyl)flavan-3,3′,4′,5,7-pentaol, was synthesized in high yield from phloroacetophenone dibenzyl ether and protoca-techualdehyde dibenzyl ether. Condensation of the 2,3-trans-3,4-cis-flavan-3,4-diol with phloroglucinol in the presence of a Lewis acid, TiCl4, proceeded with high stereoselectivity, to give only the 2,3-trans-3,4-trans isomer in over 90percnt; yield. The reactivity of this model compound might be compared with those of other model compounds to determine the effect of the hydroxyl groups in the A, B, and D rings on the reactivity of the C ring. Furthermore, this synthetic route might be applied to the synthesis of artificial tannin derivatives.