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
作者:Jan H. van der Westhuizen、Daneel Ferreira、David G. Roux
DOI:10.1039/p19810001220
日期:——
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
Synthesis of condensed tannins. Part 1. Stereoselective and stereospecific syntheses of optically pure 4-arylflavan-3-ols, and assessment of their absolute stereochemistry at C-4 by means of circular dichroism
作者:Jacobus J. Botha、Desmond A. Young、Daneel Ferreira、David G. Roux
DOI:10.1039/p19810001213
日期:——
Stereoselective and also stereospecific condensation at C-4 of flavan-3,4-diols of known absolute configuration with phloroglucinol and resorcinol in acid medium proceeds at ambient temperatures with partial retention of configuration for 2,3-trans-isomers and with inversion for 2,3-cis-analogues. Circular dichroism spectra of the resultant 4-arylflavan-3-ols all exhibit multiple Cotton effects. The