Mechanistic and Computational Studies of Exocyclic Stereocontrol in the Synthesis of Bryostatin-like <i>Cis-</i>2,6-Disubstituted 4-Alkylidenetetrahydropyrans by Prins Cyclization
作者:Yasuyuki Ogawa、Phillip P. Painter、Dean J. Tantillo、Paul A. Wender
DOI:10.1021/jo301953h
日期:2013.1.4
4-alkylidenetetrahydropyrans as sole products in excellent yields regardless of the aldehyde (R″) or syn-β-hydroxy allylsilane substituent (R′) used. By reversing the R″ and R′ groups, complementary exocyclic stereocontrol can be achieved. When the anti-β-hydroxy allylsilanes are used, the Prins cyclization gives predominantly cis-2,6-disubstituted 4-alkylidenetetrahydropyrans, now with the opposite olefin geometry
顺-β-羟基烯丙基硅烷和醛的 Prins 环化以优异的产率得到顺式-2,6-二取代的 4-亚烷基四氢吡喃作为唯一产物,而不管使用的醛 (R") 或顺-β-羟基烯丙基硅烷取代基 (R') . 通过反转 R" 和 R' 基团,可以实现互补的环外立体控制。当使用抗-β-羟基烯丙基硅烷时,Prins 环化主要产生顺式-2,6-二取代的 4-亚烷基四氢吡喃,现在具有相反的烯烃几何结构,产率很高。DFT 计算支持提出的反应机理和观察到的这些过程的立体选择性。