Synthesis of Indazolo[2,1-a]Cinnolines via Rhodium (III)-Catalyzed C-H activation/annulation under mild conditions

A simple, robust and efficient Rh(III)-catalyzed synthesis of novel 12H-indazolo[2,1-a]cinnolin-12-ones has been developed via tandem C-H activation/annulation of 2-phenylindazolones with diazo compounds by using less developed secondary amine as an intrinsic directing group. Notably, a series of nondiscriminating conditions were obtained with excellent test yield. Also, this reaction is highly regioselective with broad substrate scope and both electron-donating and electron-withdrawing groups gave satisfactory yield under very mild conditions (room temperature to 40 degrees C). It is scalable, compatible with air and H2O, and the only by-products are N-2 and H2O. Moreover, the synthesized products represent a new class of fluorophores and their initial spectroscopic characterization has been conducted. (C) 2019 Elsevier Ltd. All rights reserved.