Biflavanoids and a Linear Triflavanoid with Terminal 3,4-Diol Function

Biflavanoids and a Linear Triflavanoid with Terminal 3,4-Diol Function 

The biflavanoids with 2,3-trans-3,4-cis 2 y-trans-y,4 trans and -2, 3 -trans-y,4 Cis configurations together with the 2,3-trans-3,4-cis 2 y-trans-y,4 -trans 2 ,3 -trans-3 ,4 trans triflavanoid result from the in vitro self-condensation of the parent (2i ,3S, 4i )-3, 4, 7-trihydroxyflavan-3,4- 

The flavan-3,4-diol resists self-condensation under those conditions (0.1 M HCl, 20°, 2 -4 h) which catalyse its condensation with the fiavan-3-ol analogue, (-)-fisetinidol. A plausible explanation for this dramatic difference lies in the inductive effect of the 4-hydroxy function of the flavan-3,4-diol (or the putative 4-carbenium ion resulting from it) as potential substrate for electrophilic attack, thus reducing the nucleophilicity of the A-ring, and inhibiting the onset of self-condensation. However, once bifla-vanoid formation is initiated under more drastic conditions, the upper unit in the absence of 4-oxygenation now represents a suitable substrate for accelerated electrophilic attack and the condensation runs out of control. 

---

VI. Biflavanoids and a Linear Triflavanoid with Terminal 3,4-Diol Function. .. 60... 

---