Investigations into transition-state geometry in the Mukaiyama directed aldol reaction
Investigations into transition-state geometry in the Mukaiyama directed aldol reaction
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DOI：
10.1002/asia.200700300
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发表时间：
2008-01-01
影响因子：
4.1
通讯作者：
Lee, Wheeseong
中科院分区：
文献类型：
--
作者：
Denmark, Scott E.;Lee, Wheeseong
设计了一种模型化合物，研究了Mukaiyama羟醛缩合反应中烯醇硅烷和羰基的相对取向。环化反应必须以醛相对于烯醇硅烷的向斜或反周面取向进行。这两个方向导致非对映体的产品，从而允许明确的产品配置和过渡态几何之间的相关性。由于位阻偏置是最小的，产物分布应该反映过渡态中反应物几何形状的内在偏好。环化的模型化合物显示出适度的偏好反应通过一个反periplanar（开放过渡态）的反应物在广泛的刘易斯酸（TiCl 4，SnCl 4，SnCl 2，BF 3中心点OEt 2，TMSBr，三苯甲基高氯酸盐，EtAlCl 2）和三氟甲磺酸的存在下取向。锡（II）盐促进的环化反应是顺式选择性的，并依赖于反离子的性质。氟离子促进的反应是反选择性的，并且与阳离子的性质无关。
A model compound was designed to study the relative orientation of enol silane and carbonyl moieties in the Mukaiyama aldol reaction. The cyclization must proceed with either a synclinal or an antiperiplanar orientation of the aldehyde with respect to the enol silane. These two orientations lead to diastereomeric products, thus allowing for unambiguous correlation between product configuration and transition-state geometry. As steric bias is minimal, the product distribution should reflect the intrinsic preferences for reactant geometry in the transition state. Cyclizations of the model compound showed a modest preference for reaction via an antiperiplanar (open transition state) orientation of reactants in the presence of a wide range of Lewis acids (TiCl4, SnCl4, SnCl2, BF3 center dot OEt2, TMSBr, trityl perchlorate, EtAlCl2) and triflic acid. The cyclizations promoted by tin(II) salts were syn-selective and dependent on the nature of the counterion. Fluoride ion promoted reactions were anti-selective and were independent of the nature of the cation.