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Preparation of Substituted Indoxyls and Aminoindoles
Jr., J. S. Schneekloth, J. Kim, E. J. Sorensen*
Princeton University, USA
25 May 2009 (online)
Reported is a variation of the classical Ugi reaction, in which the nitrilium ion generated by the addition of the isocyanide to the iminium ion is interrupted by an electron-rich arene. The authors hypothesized such a trapping to proceed by replacing the carboxylic acid component with a Brønsted or a Lewis acid (J. A. Deyrup et al. Tetrahedron 1969, 25, 1467). Screening of a variety of acids led to triflic acid A as the reagent of choice. When R4 ∂ H, the imino intermediates may be hydrolyzed under mild conditions to afford substituted indoxyls. The substrate scope was fairly well studied and the reaction proceeds in yields ranging from moderate to excellent.