Synthesis of condensed tannins. Part 2. Synthesis by photolytic rearrangement, stereochemistry, and circular dichroism of the first 2,3-cis-3,4-cis-4-arylflavan-3-ols

Abstract

Photolytic rearrangements of those 2,3-trans-3,4-trans- and 2,3-trans-3,4-cis-4-arylflavan-3-ols in which the nucleophilicity of D-ring (4-aryl group) functionality exceeds that of the A-ring, provide the first access to 2,3-cis-3,4-cis-diastereoisomers. The circular dichroism of these new isomers is at variance with the proposed general rule for assessing the absolute configuration at C-4. In terms of the aromatic quadrant rule such discrepancies correlate with deviations from the preferred C-ring conformations.