Sc(OTf)3-catalyzed diastereoselective Friedel-Crafts reactions of arenes and hetarenes with 3-phenylglycidates.
Sc(OTf)3-catalyzed diastereoselective Friedel-Crafts reactions of arenes and hetarenes with 3-phenylglycidates.
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Sc(OTf)3 催化的芳烃和杂烯与 3-苯基缩水甘油酯的非对映选择性 Friedel-Crafts 反应
DOI：
10.1039/c2ob25988e
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发表时间：
2012
影响因子：
3.2
通讯作者：
T. Bach
中科院分区：
文献类型：
--
作者：
D. Wilcke;T. Bach
制备了五种不同的对位取代的3-苯基缩水甘油酯（3-苯基环氧乙烷-2-羧酸酯），并在路易斯酸催化下与芳烃和杂烯进行反应。发现 Sc(OTf)3 可有效（5 mol%）促进以硝基甲烷为溶剂的弗里德尔-克来福特反应。该反应显示立体会聚进行，这使得苄基阳离子可能成为中间体。非对映选择性根据亲核试剂和 3-芳基缩水甘油酯的选择而变化。使用 3-茴香基缩水甘油酸叔丁酯获得了最佳结果，其在非对映体比率 (d.r.) 之间提供了在 82 : 18 和 >95 : 5 之间具有高顺式偏好的相应产品。观察到的选择性可以通过模型来解释，根据该模型，中间苯甲基阳离子采用首选构象，这允许通过相邻立体异构体进行非对映面分化中心。
Five different para-substituted 3-phenylglycidates (3-phenyloxirane-2-carboxylates) were prepared and subjected to reactions with arenes and hetarenes under Lewis acid catalysis. Sc(OTf)3 was found to effectively (5 mol%) promote a Friedel–Crafts reaction in nitromethane as the solvent. The reaction was shown to proceed stereoconvergently, which makes the intermediacy of a benzylic cation likely. The diastereoselectivities varied depending on the choice of the nucleophile and 3-arylglycidate. Best results were obtained with tert-butyl 3-anisylglycidate, which delivered the respective products with high syn-preference in diastereomeric ratios (d.r.) between 82 : 18 and >95 : 5. The observed selectivity can be explained by a model, according to which the intermediate benzylic cations adopt a preferred conformation, which allows for diastereoface-differentiation by the adjacent stereogenic center.