Ru(II)- and Rh(III)-Catalyzed C–H Activation/Annulation of Pyrazolidinones with CF ₃ -Imidoyl Sulfoxonium Ylides

A catalytic system-controlled C-H activation and cascade annulation strategy for the synthesis of 5-substituted or 5,10-disubstituted pyrazolo[1,2-<i>a</i>]cinnolines is disclosed herein. A series of novel trifluoromethyl-substituted pyrazolo[1,2-<i>a</i>]cinnolines were successfully obtained utilizing a Ru(II)-catalyst and CF₃-imidoyl sulfoxonium ylides. In the Rh(III)-catalytic system, 5-trifluoromethyl-10-enyl substituted pyrazolo[1,2-<i>a</i>]cinnolines were effectively constructed. Possible reaction mechanisms for the formation of both kinds of products were proposed based on preliminary mechanistic studies. These methods feature excellent regioselectivity, mild reaction conditions, broad substrate scope, operational simplicity, and facile product availability, providing practical access to structurally diverse pyrazolo[1,2-<i>a</i>]cinnolines.