A diastereoselective metal-catalyzed [2+2] cycloaddition of bis-enones
A diastereoselective metal-catalyzed [2+2] cycloaddition of bis-enones
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DOI：
10.1021/ja010800p
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发表时间：
2001-07-11
影响因子：
15
通讯作者：
Krische, MJ
中科院分区：
文献类型：
--
作者：
Baik, TG;Luis, AL;Krische, MJ
虽然光化学促进的分子内烯烃[2+ 2]环加成通常用于合成复杂的分子结构，但金属催化的系链烯烃[2+ 2]环加成尚未被描述。2,3迄今为止，金属催化的烯烃[2+ 2]环加成仅限于张力烯烃（降冰片二烯或亚甲基环丙烷）和缺电子烯烃的分子间反应，通常使用零价镍催化剂。最近，手性路易斯酸被证明可以催化缺乏电子的烯烃和乙烯基硫化物或缩醛缩硫烯之间的分子间[2+ 2]环加成反应。在这篇文章中，我们提出了第一个分子内金属催化的烯烃[2+ 2]环加成反应。这种方法可以方便地构造取代的双环[3.2]。[0]非对映纯形式的环体系。最近，我们的实验室报道了非对映选择性（双酮ato）金属催化的醛醇和迈克尔环还原。5在优化双烯酮1a和2a的Michael环还原过程中，有以下观察结果：当使用2.4当量的苯硅烷时，Michael环还原反应代表了唯一的反应途径，而在1.2当量的苯硅烷存在下进行的反应产生了相当数量的环还原反应，值得注意的是，产生了[2+ 2]环加成产物。对[2+ 2]环加法流形进行了优化设计。进一步减少苯硅烷的用量并没有实质性地改变产物的比例，而是导致两种产物的产率下降。在没有硅烷的情况下，没有观察到反应。筛选了不同硅烷源诱导[2+ 2]环加成途径选择的能力。[2+ 2]环加物1b和2b的最佳产率为4.0当量的苯基甲基硅烷
While photochemically promoted intramolecular alkene [2+ 2] cycloadditions are routinely used in the synthesis of complex molecular architectures, 1 related metal-catalyzed [2+ 2] cycloadditions of tethered alkenes have not been described. 2, 3 To date, metal-catalyzed alkene [2+ 2] cycloadditions have been restricted to the intermolecular reaction of strained alkene (norbornadienes or methylenecyclopropanes) and electron-deficient alkene partners, typically using zero-valent nickel catalysts. 4 More recently, chiral Lewis acids have been shown to catalyze the enantioselective intermolecular [2+ 2] cycloaddition between electron deficient alkenes and vinylsulfides or thioketene acetals. 2c In this account, we present the first intramolecular metal-catalyzed [2+ 2] cycloaddition of alkenes. This methodology allows for the facile construction of substituted bicyclo [3.2. 0] ring systems in diastereomerically pure form.Diastereoselective (diketonato) metal-catalyzed aldol and Michael cycloreductions recently were reported from our labs. 5 In the course of optimizing the Michael cycloreduction of bis-enones 1a and 2a, the following observations were made. Whereas Michael cycloreduction represents the exclusive reaction pathway when 2.4 equiv of phenylsilane are used, reactions conducted in the presence of 1.2 equiv of phenylsilane gave comparable amounts of cycloreduction and, remarkably,[2+ 2] cycloaddition products. Attempts were made to optimize the [2+ 2] cycloaddition manifold. Further decreasing the amount of phenylsilane did not substantially alter the product ratio and resulted in diminished yields of both products. In the absence of silane, no reaction was observed. Alternative silane sources were screened for their capacity to induce selection of the [2+ 2] cycloaddition pathway. Optimal yields of the [2+ 2] cycloadducts 1b and 2b were obtained with 4.0 equiv of phenylmethylsilane in the