TiCl₃-Mediated Reductive Aminohydroxylation of Alkenes to (Benzo)Furo[3,2-b]Indolines

We report a TiCl₃-mediated reductive double cyclization of ortho-nitroaryl-substituted styrene and stilbene derivatives that enables efficient access to dihydrofuro[3,2-b]indolines and benzofuro[3,2-b]indolines under mild conditions. The transformation proceeds through a single-electron transfer (SET) reduction of the nitro group to a nitroso intermediate, followed by a concerted 5-center, 6π-electrocyclization to generate a nitrone. Intramolecular trapping of this nitrone by a tethered hydroxy or phenol group forms a cyclic hydroxylamine, which undergoes further SET reduction to furnish the fused indoline products. This domino reductive cascade provides a mechanistically distinct and complementary alternative to established oxidative methods for constructing [3,2-b] fused indoline architectures.