An anhydride-promoted traceless hydrazine–I/Br exchange strategy is reported, where hydrazine hydrate and cyclic/linear iodonium, including rarely explored cyclic bromonium, are converted to benzo­[c]­cinnolines/azobenzenes in one pot. The reaction proceeds through diacylation (first and second CN formation), N,N′-diarylation (third and fourth CN formation), and deacylation/oxidation (2 CN cleavages and 1 NN formation). The reaction mechanism is investigated by isolating multiple intermediates and kinetic studies. Furthermore, time-dependent electrospray ionization mass spectrometry (TD ESI-MS) was applied to track the process by detecting most intermediates. The complex [CuIII(iodobiphenyl)­(bipy)­I]+ (Int-C) was detected for the first time, giving evidence for oxidative addition of cyclic iodonium to Cu catalyst. Another complex [CuI(PHA)­(bipy)] (Int-B) via ligand-exchange between the hydrazide and Cu catalyst was also detected, indicating a two-path initial activation process.

A dual ring-opening, decarboxylative/decarbonylative [3 + 4] annulation of readily available (6-membered) isatoic anhydrides with (5-membered) cyclic iodoniums to efficiently build (7-membered) tribenzo[b,d,f]azepines through Pd(0) catalysis is disclosed. The tandem...