Department Chemie and Catalysis Research Center, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany.
Org Biomol Chem. 2012 Aug 28;10(32):6498-503. doi: 10.1039/c2ob25988e. Epub 2012 Jul 2.
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.
五种不同的对位取代的 3-苯代缩水甘油酸酯（3-苯氧环丙烷-2-羧酸酯）被制备出来，并在路易斯酸催化下与芳烃和杂芳烃反应。研究发现，Sc(OTf)3（三氟甲磺酸钪）在作为溶剂的硝基甲烷中可以有效地（5 mol%）促进傅-克反应。反应表现出立体协同性，这使得苄基阳离子中间体很有可能存在。非对映选择性取决于亲核试剂和 3-芳基缩水甘油酸酯的选择。用叔丁基 3-茴香基缩水甘油酸酯得到了最好的结果，以高 syn-选择性获得了相应的产物，非对映体比率（d.r.）在 82 : 18 和 >95 : 5 之间。观察到的选择性可以通过一个模型来解释，根据该模型，中间体苄基阳离子采用一种优先的构象，允许相邻的立体中心进行非对映面差异。
