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。