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 Cdouble bond; length as m-dashN bond and nitro group, both of which were easily achieved in one-pot by controlling the pH of the reaction mixture.