A cascade dehydrative [3+2] annulation reaction of N-substituted arylhydroxylamines and activated alkynes was developed for the synthesis of indole under catalyst-free conditions, water as the the only by-product during this transformation.

Abstract

An efficient approach for the synthesis of indole by the annulation of N-substituted hydroxylamine with activated alkynes under mild reaction conditions was established without the additional catalyst or chemical reagents. Both 3-substituted and 2,3-disubstituted indoles were obtained with good-to-excellent isolated yields by using the terminal and internal electron-deficient alkynes, respectively. This novel and green protocol provides a rapid, mild, and efficient method for the construction of indole heterocycles.