Palladium-Catalyzed Indole and Azaindole Synthesis by Direct Annulation of Electron-Poor 0-Chloroanilines and 0-Chloroaminopyridines with Aldehydes

摘要

A practical process for the synthesis of 2-unsubstituted indoles and azaindoles has been developed by the palladium-catalyzed direct annulation of electron-poor o-chloro/bromoanilines and o-chloroaminopyridines with aldehydes. Coupled with the previous results of Jia and Zhu, this allows rapid access to a variety of 2-unsubstituted indoles and azaindoles starting from simple and easily accessible precursors.The indole nucleus is a prominent structural motif abundantly found in a wide variety of bioactive natural products and pharmaceuticals.1 After extensive research over a hundred years, a variety of well-documented methods for the preparation of functionalized indoles are now available.2 However, the development of general, mild, and efficient methods from simple and easily accessible precursors are of continued interest.3 In this context, palladium-catalyzed reactions, generally tolerant of many functional groups, are widely applied to the preparation of the indole scaffold and provide alternatives to traditional methods.