Efficient Reagents for the Synthesis of 5-, 7-, and 5,7-Substituted Indoles Starting from Aromatic Amines: Scope and Limitations
作者:Jesús Ezquerra、Concepción Pedregal、Carlos Lamas、José Barluenga、Marta Pérez、Miguel Angel García-Martín、José M. González
DOI:10.1021/jo952119+
日期:1996.1.1
Upon reaction with IPy(2)BF(4), 4-substituted anilines give regioselectively the corresponding o-iodoanilines in nearly quantitative yield, in a process that can be carried out on a multigram scale. Palladium-catalyzed coupling of the resulting 2-iodoanilines with (trimethylsilyl)acetylene (TMSA), followed by efficient CuI-mediated nitrogen cyclization onto alkynes with concurrent elimination of the TMS substituent, allows a straightforward elaboration of 5-mono- and 5,7-disubstituted indoles from aromatic amines. This new approach to the aforementioned indoles does not requires protective groups on nitrogen at any step and can be adapted for preparing related 7-manosubstituted indoles. Moreover, examples iterating the process are given, allowing bis-annulation and sequential double annulation and resulting in synthesis of benzodipyrroles. Additionally, suitable conditions for iodination of some of the target indoles with IPy(2)BF(4) are discussed.