Ragaini Fabio, Rapetti Andrea, Visentin Elena, Monzani Michela, Caselli Alessandro, Cenini Sergio
Dipartimento di Chimica Inorganica, Metallorganica e Analitica, Università di Milano, and ISTM-CNR, Via Venezian 21, 20133 Milano, Italy.
J Org Chem. 2006 May 12;71(10):3748-53. doi: 10.1021/jo060073m.
Palladium-phenanthroline complexes efficiently catalyze the reaction of nitroarenes with arylalkynes and CO to give 3-arylindoles by an ortho-C-H functionalization of the nitroarene ring. Both electron-withdrawing and electron-donating substituents are tolerated on the nitroarene, except for bromide and activated chloride. Nitroarenes bearing electron-withdrawing substituents react faster, but the selectivity of the reaction depends on both polar and radical stabilization effects. Among those tested, only arylalkynes afforded indoles under the investigated conditions. The reaction mechanism was partly investigated. The kinetics is first order in nitroarene concentration and the rate-determining step of the cycle is the initial nitroarene reduction. No primary isotope effect is observed on either rate or selectivity, implying that the cyclization step is fast.
钯-菲咯啉配合物通过硝基芳烃环的邻位C-H官能化反应，有效地催化硝基芳烃与芳基炔烃和CO反应生成3-芳基吲哚。除了溴化物和活性氯化物外，吸电子和供电子取代基在硝基芳烃上均能耐受。带有吸电子取代基的硝基芳烃反应更快，但反应的选择性取决于极性和自由基稳定化效应。在所测试的物质中，在研究条件下只有芳基炔烃能生成吲哚。对反应机理进行了部分研究。动力学对硝基芳烃浓度呈一级反应，该循环的速率决定步骤是初始的硝基芳烃还原反应。在速率或选择性上均未观察到一级同位素效应，这意味着环化步骤很快。
