An efficient and convenient synthesis of heterocycle-fused indazoles via the N–N bond forming reaction of nitroarenes induced by low-valent titanium reagent

A mild and efficient one-pot protocol for the preparation of 8,13-dihydro-7H-indolo[2′,3′:3,4]pyrido[1,2-b]indazole and 5,6-dihydroindazolo[3,2-a]isoquinoline via the reductive cyclization of nitro-aryl substrates mediated by a low-valent titanium reagent has been developed. The attractive features of the current method include an N–N bond formation and the selective reduction of the CN bond and nitro group, both of which were easily achieved in one-pot by controlling the pH of the reaction mixture.

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