Copper-Catalyzed Three-Component Coupling Synthesis of 3-Aminoindol(in)es

Significance

Reported is an efficient copper-­catalyzed route to 3-aminoindolines by a three-component coupling of N-protected ortho-­aminobenzaldehydes, secondary amines, and ­terminal acetylenes. The reaction conditions, although briefly optimized, are exactly the same as those described for the synthesis of benzofurans using a three-component coupling approach, but with ortho-hydroxybenzaldehydes (N. Sakai, N. Uchida, T. Konakahara Tetrahedron Lett. 2008, 49, 3437). The yields range from poor to almost quantitative. 3-Aminoindoles were synthesized in one pot by in situ isomerization of the indolines using cesium carbonate. Interestingly, detosylation-isomerization of an N-tosyl indoline was achieved in quantitative yield using magnesium powder (B. Nyasse, L. Grehn, U. Ragnarsson J. Chem. Soc., Chem. Commun. 1997, 1017) ­under sonication.