Controlling the regioselectivity of the ring opening of spiro-epoxyoxindoles for efficient synthesis of C(3)-N(1')-bisindoles and C(3)-N(1')-diindolylmethane.

An efficient strategy for the construction of both C(3)-N(1') bisindoles and C(3)-N(1') diindolylmethane has been explored via proper tuning of the nucleophilicity of indoline/indole to spiro-epoxyoxindole. Lewis acid-catalyzed highly regio- as well as chemoselective coupling at the C-3 centre of spiro-epoxyoxindoles with indolines furnishes C(3)-N(1') bisindoles whereas base mediated and Lewis acid-catalyzed regioselective coupling at the less hindered site of spiro-epoyoxindoles with indoles via the S2 mechanism provides C(3)-N(1') diindolylmethane.