Reversal of Selectivity in C3-Allylation and Formal [3+2]-Cycloaddition of Spiro-epoxyoxindole: Unified Synthesis of Spirofuranooxindole, (±)-N-Methylcoerulescine, (±)-Physovenine, and 3a-Allylhexahydropyrrolo[2,3-b]indole

An effective Lewis acid catalyzed regioselective C3-allylation and a formal [3 + 2]-annulation reaction of spiro-epoxyoxindoles have been developed and can be accessed simply by changing the reaction conditions. This method has been successfully employed for the synthesis of spiro(pyrrolidinyloxindole), 3a-allylhexahydropyrrolo[2,3-b]indole, and furanoindoline.