While hundreds of literature reports describe the preparation of spirooxindole-based 5- and 6-membered-heterocycles, construction of 7-membered-heterocyclic rings spiro-connected to an oxindole core has been far less developed. Herein, we disclose a base-mediated (4+3) annulation of spiro-epoxyoxindoles and 2-(o-fluorophenyl)benzimidazoles or o-fluorobenzenesulfonamides toward synthesis of two new classes of spirooxindole-based polycyclic systems. Mechanistically, this conceptually simple and high atom-economical reaction proceeds via an SN2-like intermolecular epoxide ring-opening, concomitantly followed by an intramolecular SNAr reaction. From a synthetic aspect, the notable features of the process are its full regioselectivity, operational simplicity using readily available substrates under transition-metal-free conditions, high yields and wide substrate scope.

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