A novel ruthenium(Ⅱ)?catalyzed C-H/C-N annulation of 1?phenyl?2?pyrazolin?5?one with ethylene carbonate was designed. In this transformation, the vinylene carbonate acts as an ethynol or alkyne surrogate without any external oxidant as well as bases involved. The reaction exhibits a broad substrate scope with excellent functional group compatibility, affording a series of 1H?pyrazolo[1,2?a]cinnolin?1?ones in 42%~87% yields. A possible mechanism involving a sequential C-H activation/intramolecular C-N bond formation/ CO₂ or CO {}_{\mathrm{3}}^{\mathrm{2}-} elimination is proposed. In addition, the reaction can also be carried out on a gram scale with satisfactory yield.