Formal Dehydrative [3+2] Annulation of <i>N</i> ‐Arylhydroxamine and Activated Alkyne Toward Indole

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.