ChemInform Abstract: A New Synthesis of 3-Fluoro- and 3-Chlorocyclobutenes from Dihalocyclobutanes. The Five Isomers of Chlorofluorocyclobutane

3-Fluorocyclobutene (1) and 3-chlorocyclobutene (2) have been obtained by simpler syntheses and in higher yield than previously reported. One of the synthetic steps involves a three-phase-transfer-catalysis technique that could be of wider utility. New examples are cited of applying AgF2, an underutilized reagent, as a fluorinating agent near room temperature. Compounds 1 and 2 have been characterized by mass, NMR and vibrational spectroscopies. The NMR spectra have been fully analyzed. Useful group frequencies in the vibrational spectra of halocyclobutenes have been identified. The five monochloro- monofluorocyclobutane precursors of fluorocyclobutenes have also been separated and characterized. From NMR coupling constants, conformer mixtures have been identified for three of the isomers.