Controlling the regioselectivity of the ring opening of spiro-epoxyoxindole for efficient synthesis of C(3)–N(1′)-bisindole and C(3)–N(1′)-diindolylmethane

A concise synthetic strategy for the construction of both C(3)–N(1′) bisindoles and C(3)–N(1′) diindolylmethane have been explored via proper tuning of the nucleophilicity of indoline/indole to spiro-epoxyoxindole. Lewis acid-catalyzed coupling of spiro-epoxyoxindole with indoline furnishes C(3)–N(1′) bisindoles whereas base mediated, and Lewis acid-catalyzed coupling of spiro-epoyoxindole with indole provides C(3)–N(1′) diindolylmethane.