Copper-Catalyzed Oxidative (4 + 2) Cycloaddition of 2-Arylindoles and 2-Aminophenols To Prepare Indole-Fused 1,4-Benzoxazines

Herein, we reported a copper(I)-catalyzed oxidative (4 + 2) cycloaddition of 2-aryl indoles and 2-aminophenols to prepare a variety of indole-fused 1,4-benzoxazines containing a quaternary carbon stereocenter in moderate to excellent yields in the presence of t-butyl nitrite (TBN) as an oxidant. Mechanistic studies indicated that the reaction involved a TBN-mediated nitrosation, copper-catalyzed condensation, and subsequent intramolecular cyclization in a one pot. Moreover, the obtained indole-fused 1,4-benzoxazine can be easily converted into angularly fused 6-5-5 tricyclic scaffold in a total 50% yield over two steps.