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Regioselective Synthesis of Elusive 4,9-Dihydro-1 H -Carbazoles by Gold-Catalyzed Cycloisomerization of 3-Allenylmethylindoles

2013; American Chemical Society; Volume: 78; Issue: 19 Linguagem: Inglês

10.1021/jo401388b

1520-6904

Estela Álvarez, Patricia García‐García, Manuel A. Fernández‐Rodríguez, Roberto Sanz,

Cyclopropane Reaction Mechanisms

A general and efficient synthesis of 4,9-dihydro-1H-carbazoles from 3-allenylmethylindoles is reported. The process, catalyzed by a cationic gold(I) complex, involves a formal C2-H bond activation of the indole unit by reaction with the allene. The nature of the substituents at the allylic and terminal positions of the allene moiety has a crucial effect on the regioselectivity of the cyclization, which is also influenced by the catalyst and the solvent employed. Moreover, some evidence of the contribution of different reaction routes is provided, which led us to propose a plausible multipathway mechanism consistent with all of the results described.