4-Trifluoromethyl-2 (5H)-furanone (2) and 4-trifluoromethyl-N-substituted dihydropyrrol-2-ones (4) were effectively prepared from ethyl (Z)-4-bromo-3-trifluoromethyl-2-butenoate (1). The dihydropyrrol-2-ones (4) were found to consist of the Δ3-and/or Δ4-form, and the electronic nature of the substituent on nitrogen affected the isomer ratio.