Synthesis of condensed tannins. Part 4. A direct biomimetic approach to [4,6]- and[4,8]-biflavanoids
作者:Jacobus J. Botha、Daneel Ferreira、David G. Roux
DOI:10.1039/p19810001235
日期:——
their condensation with nucleophilic flavan-3-ols to form [4,6]- and [4,8]-biflavanoids at ambient temperatures and under mildly acidic aqueous conditions apparently simulates the initial step in condensed tannin formation in a number of natural sources. The stereospecificity (or stereoselectivity) of the reaction is conditioned mainly by the 2,3-cis or 2,3-trans stereochemistry of the parent flavan-3
在环境温度和温和条件下,由flavan-3,4-二醇生成flavanyl-4-carbo-阳离子并与亲核flavan-3-ol缩合形成[4,6]-和[4,8]-双黄烷酮。酸性水溶液条件显然模拟了许多天然来源中单宁缩合形成的初始步骤。反应的立体特异性(或立体选择性)主要取决于母体flavan-3,4-二醇的2,3-顺式或2,3-反式立体化学,但也取决于flavan-3-ol的亲核性,和其空间专一性(或区域选择性)过程是由黄烷-3-醇的感受性A环取代取代变化引起的空间因素引起的。