Development of hydrogen transfer reactions catalyzed by iridium complexes and their applications to the synthesis of nitrogen heterocycles

近年来，含五甲基环戊二烯(CP^*)配体的Ir络合物的化学研究引起了人们的广泛关注。在化学研究过程中，我们发现[Cp^*IrCl2]2对有机分子间的氢转移反应具有催化活性。在本研究项目中，我们研究了Cp^*Ir络合物催化的氢转移反应及其在氮杂环合成中的应用。首先，我们发现了一种新的氨基醇的催化氧化环化反应。以2-氨基苯乙醇为原料，在[Cp^*IrCl2]2/K2CO3催化体系下，以较高的产率合成了吲哚类化合物。该催化体系对3-(2-氨基苯基)丙醇合成1，2，3，4-四氢喹啉和4-(2-氨基苯基)丁醇合成2，3，4，5-四氢-1-苯并氮杂环己烷反应也是有效的。例如，在催化量的[Cp^*IrCl2]2和K2CO3存在下，苯胺与苯甲醇反应生成N-苯基苯胺，产率很高。在上述结果的基础上，我们找到了伯胺与二醇N-杂环化反应的新催化体系。以1，4-，1，5-和1，6-二元醇为原料，在Cp^*Ir催化剂和碱的作用下，以较高的产率合成了吡咯烷、哌啶、氮杂环己烷和吗啉衍生物。以Cp^*Ir为催化剂，通过区域和化学选择性转移氢化反应，以较高的产率合成了1，2，3，4-四氢喹啉衍生物。

In recent years, much attention has been focused on the chemistry of iridium complexes bearing a pentamethylcyclopentadienyl (Cp^*) ligand. During the course of our investigation on the chemistry of Cp^* iridium complexes, we found a catalytic activity of [Cp^*IrCl_2]_2 toward hydrogen transfer reactions between organic molecules. In this research project, we have studied on the hydrogen transfer reactions catalyzed by Cp^* iridium complexes and their applications to the synthesis of nitrogen heterocycles.First, we have found a new catalytic oxidative cyclization of amino alcohols. Indole derivatives were synthesized in good to excellent yields from 2-aminophenethyl alcohols by means of a [Cp^*IrCl_2]_2 / K_2CO_3 catalytic system. This catalytic system was also effective for syntheses of 1,2,3,4-tetrahydroquinolines from 3-(2-aminophenyl)propanols and 2,3,4,5-tetrahydro-1-benzazepine from 4-(2-aminophenyl)butanol.Next, we have found an efficient catalytic system for N-alkylation of primary amines with alcohols. As an example, the reaction of aniline with benzyl alcohol in the presence of catalytic amounts of [Cp^*IrCl_2]_2 and K_2CO_3 gave N-benzylaniline in excellent yield. This catalytic system was applicable to a wide variety of amines and alcohols.On the basis of above results, we have found a new catalytic system for N-heterocyclization of primary amines with diols. Pyrrolidine, piperidine, azepane and morpholine derivatives could be synthesized in good yields by the reaction of benzylamine with 1,4-, 1,5-and 1,6-diols in the presence of Cp^*Ir catalyst and base.We also examined the transfer hydrogenation of quinolines using 2-propanol as a hydrogen source. 1,2,3,4-Tetrahydroquinoline derivatives were synthesized in good yields by regio-and chemoselective transfer hydrogenation catalyzed by Cp^*Ir catalyst.