Small-Ring Compounds. XXXI. Cyclobutane Derivatives from Adducts of Cyclohexenylacetylene and Fluorochloroethylenes

Cycloadditions of 1-ethynylcyclohex-1-ene with trifluorochloroethylene and difluorodichloroethylene gave 1,1,2 trifluoro-2-chloro- (IV) and 1,1-difluoro-2,2-dichloro-3(cyclohex-1-enyl-cyclobutene (XI), respectively. Both IV and XI were hydrolyzed by sulfuric acid to the corresponding monoketones, 2-fluoro-2-chloro- and 2,2-dichloro-3-(cyclohex-1-enyl)-cyclobutenones. With iodide and ethoxide ions IV or XI appeared to give S_N2' displacement products. Diels-Alder adducts were obtained from IV and maleic anhydride or dicarbethoxyacetylene. The triethylamine-catalyzed rearrangement of XI at 150º gave 1,1 difluoro-2,4-dichloro-3-(cyclohex-1-enyl)-cyclobutene (XXXI), but at 180º an unexpected elimination rearrangement led to 2-fluoro-1,3-dichloro-5,6,7,8-tetrahydronaphthalene (XXXIII).