An unconventional [2 + 3] cyclization of pyridinium ylides with 2-ylideneoxindoles has been developed for the facile construction of pharmacologically interesting polysubstituted 9-pyrrolo[1,2-]indol-9-ones (fluorazones). Mechanistic studies revealed that the reaction, which has a broad substrate scope, proceeds via intermolecular [1,4]-sulfonyl transfer. Moreover, biological evaluation showed that polysubstituted fluorazone potently inhibits indoleamine 2,3-dioxygenase 1, kynurenine production, and immunotolerance in tumors.
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