Synthetic studies of proanthocyanidins. Part 2: Stereoselective gram-scale synthesis of procyanidin-B3
作者:Akiko Saito、Noriyuki Nakajima、Akira Tanaka、Makoto Ubukata
DOI:10.1016/s0040-4020(02)00936-5
日期:2002.9
A stereoselective synthesis of procyanidin-B3, a condensed catechin dimer, is described. Condensation of benzylated catechin with various 4-O-alkylated flavan-3,4-diol derivatives as an electrophile in the presence of a Lewis acid led to protected procyanidin-B3 and its diastereomer. In particular, the reaction using (2R,3S,4S)-3-acetoxy-5,7,3′,4′-tetrabenzyloxy-4-(2″-ethoxyethoxy)flavan as an electrophile
描述了花青素-B3(一种儿茶素缩合二聚体)的立体选择性合成。在路易斯酸的存在下,苄基儿茶素与各种4 - O-烷基化的flavan-3,4-二醇衍生物作为亲电试剂的缩合导致被保护的原花青素-B3及其非对映异构体。特别地,在TMSOTf存在下,使用(2 R,3 S,4 S)-3-乙酰氧基-5,7,3',4'-四苄氧基-4-(2“-乙氧基乙氧基)黄酮作为亲电试剂的反应在-78℃下,得到具有高立体选择性和优良分离产率的八-O-苄基化花青素-B3。此外,我们成功地完成了保护性原花青素B3的立体选择性克级合成。