Rh(III)- or Ru(II)-Catalyzed\nC–H Annulation\nwith Vinylene Carbonate and an Unexpected Aerobic Oxidation/Deprotection\nCascade to Yield Cinnolin-4(1<i>H</i>)‑ones

Transition metal-catalyzed C–H annulation reactions\nhave\nbeen extensively utilized for the synthesis of cinnolines, especially\nthe N-protected ones; however, none of them can yield cinnolin-4(1<i>H</i>)-ones, a significant class of bioactive skeletons. Herein,\nwe disclose one-pot access to cinnolin-4(1<i>H</i>)-ones\nthrough Rh(III)- or Ru(II)-catalyzed C–H activation/annulation\nof <i>N</i>-aryl cyclic hydrazides with vinylene carbonate,\nfollowed by an O<sub>2</sub>/K<sub>2</sub>CO<sub>3</sub>-promoted\naerobic oxidation/deprotection cascade. The π-conjugation of\nthe directing groups plays a crucial role in facilitating this transformation.\nNotably, seven-membered enolic Rh species <b>IMC</b> is characterized\nvia electrospray ionization mass spectroscopy for the first time,\nwhich, along with systematic control experiments, provides compelling\nevidence for the mechanistic pathway encompassing alkenyl insertion,\nβ-oxygen elimination, protonation, and dehydration.