研究室工作進展 Dec. 21st, 2012.

 Cyclopentadiene-Phosphine/Palladium Catalyzed Cleavage of C-N Bonds in Secondary Amines: Synthesis of Pyrrole and Indole Derivatives from Secondary Amines and Alkenyl or Aryldibromides

 Weizhi Geng, Wen-Xiong Zhang, Wei Hao, Zhenfeng Xi*

 J. Am. Chem. Soc. 2012, 134, 20230-20233.

The cleavage of carbon–nitrogen (C–N) bonds is of significant synthetic interest, because such bonds are common in organic chemistry and usually unreactive. There was no report in the literature on transition-metal catalyzed cleavage and synthetic applications of C(sp3)–N bonds in secondary amines. Since a secondary amine contains one N–H bond and two C–N bonds, their efficient selective cleavage and further synthetic applications are very attractive for both mechanistic study and synthetic chemistry.

In this work, an efficient Pd–catalyzed cleavage of C(sp3)–N bonds in secondary amines and consequent C(sp2)–N and C(sp3)–N coupling process was developed. Various secondary amines could be used to react with alkenyl or aryl dibromides affording pyrroles and indoles in high yields. Cyclopentadiene-phosphine ligands, a new type of P–olefin ligands, were designed and found to be able to remarkably promote the efficiency of this Pd–catalyzed process. A reactive Pd complex coordinated with a cyclopentadiene-phosphine ligand was successfully isolated and structurally characterized.

亮點介紹

通過我們自己發展的方法，設計、合成獨特的配體是本組近年來一直在思考的課題。本工作利用本組發展的方法(Xi, Z.; Li, P. Angew. Chem. Int. Ed. 2000, 39, 2950; Zhao, C.; Li, P.; Cao, X.; Xi, Z. Chem. Eur. J. 2002, 8, 4292.)，設計合成了一類分子内含有多取代環戊二烯（雙烯）以及膦原子的新型配體。利用該配體與钯的催化體系，首次實現了二級胺中Csp3-N鍵的催化選擇性切斷，合成了一系列N上具有不同取代基的吡咯和吲哚衍生物。利用同樣的方法，我們合成的具有不同取代基的多取代環戊二烯也表現出不同與一般環戊二烯配體的獨特性質（Xu, L.; Wang, Z.; Zhang, W.-X.; Xi, Z. Inorg. Chem. 2012, 51, 11941）。

   膦-烯雙配配體近年來在過渡金屬催化的有機合成反應中顯示出獨特性質。預期該類新型配體（膦-環戊二烯）将在更多的過渡金屬催化的有機合成反應中顯示獨特的作用。