Flash vacuum pyrolysis of a mixture of-argon and 5-acetoxy-1,5-dihydro-2H-pyrrol-2-one at 350 degrees C and condensation of the pyrolysate onto a cold plate at 12 K produces acetic acid and 2-azacyclopenta-2,4-dien-1-one (2H-pyrrol-2-one, 2), identified by IR spectroscopy. Ab initio calculations for 2 and cyclopentadienone at the MP2/6-31G** level successfully reproduce the observed IR spectra. Photochemically 2 is converted to acetylene, HCN, and CO. Attempts to chemically trap 2 have so far been unsuccessful.