Rh(III)- or Ru(II)-Catalyzed C–H Annulation with Vinylene Carbonate and an Unexpected Aerobic Oxidation/Deprotection Cascade to Yield Cinnolin-4(1<i>H</i>)-ones

Transition metal-catalyzed C-H annulation reactions have been extensively utilized for the synthesis of cinnolines, especially the N-protected ones; however, none of them can yield cinnolin-4(1<i>H</i>)-ones, a significant class of bioactive skeletons. Herein, we disclose one-pot access to cinnolin-4(1<i>H</i>)-ones through Rh(III)- or Ru(II)-catalyzed C-H activation/annulation of <i>N</i>-aryl cyclic hydrazides with vinylene carbonate, followed by an O₂/K₂CO₃-promoted aerobic oxidation/deprotection cascade. The π-conjugation of the directing groups plays a crucial role in facilitating this transformation. Notably, seven-membered enolic Rh species <b>IMC</b> is characterized via electrospray ionization mass spectroscopy for the first time, which, along with systematic control experiments, provides compelling evidence for the mechanistic pathway encompassing alkenyl insertion, β-oxygen elimination, protonation, and dehydration.