Lam Yu-hong, Cheong Paul Ha-Yeon, Blasco Mata José M, Stanway Steven J, Gouverneur Véronique, Houk K N
Chemistry Research Laboratory, University of Oxford, UK.
J Am Chem Soc. 2009 Feb 11;131(5):1947-57. doi: 10.1021/ja8079548.
The Diels-Alder reactions of a series of silyloxydienes and silylated dienes with acyclic alpha,beta-unsaturated ketones and N-acyloxazolidinones have been investigated. The endo/exo stereochemical outcome is strongly influenced by the substitution pattern of the reactants. High exo selectivity was observed when the termini of the diene and the dienophile involved in the shorter of the forming bonds were both substituted, while the normal endo preference was found otherwise. The exo-selective asymmetric Diels-Alder reactions using Evans' oxazolidinone chiral auxiliary furnished a high level of pi-facial selectivity in the same sense as their well-documented endo-selective counterparts. Computational results for these Diels-Alder reactions were consistent with the experimental endo/exo selectivity in most cases. A twist-asynchronous model accounts for the geometries and energies of the computed transition structures.
研究了一系列甲硅烷氧基二烯和甲硅烷基化二烯与无环α,β-不饱和酮及N-酰基恶唑烷酮的狄尔斯-阿尔德反应。内型/外型立体化学结果受反应物取代模式的强烈影响。当参与形成较短键的二烯和亲双烯体的末端均被取代时，观察到高外型选择性，否则则呈现正常的内型偏好。使用伊文斯恶唑烷酮手性助剂的外型选择性不对称狄尔斯-阿尔德反应，与已充分记录的内型选择性反应类似，提供了高水平的π-面选择性。这些狄尔斯-阿尔德反应的计算结果在大多数情况下与实验得到的内型/外型选择性一致。一个扭曲异步模型解释了计算得到的过渡结构的几何形状和能量。
