Partially fluorinated heterocyclic compounds. Part 20. Isomerisations of pentafluorophenyl and 1,3,4,5,6,7,8-heptafluoro-2-naphthyl prop-2-ynyl ethers. Reactions of the naphthyl ether and 2-fluoromethyl-4,5,6,7,8,9-hexafluoro-naphtho[2,1-b]furan with 2,3-dimethylbut-2-ene and with 3,3-dimethylbut-1-ene

Abstract

Pentafluorophenyl prop-2-ynyl ether (1) has been isomerised to 4,5,6,7-tetrafluoro-2-fluoromethyl-benzo[b]furan (2) in a liquid phase reaction while 1,3,4,5,6,7,8-heptafluoro-2-naphthyl prop-2-ynyl ether (3) gave 4,5,6,7,8,9-hexafluoro-2-fluoromethylnaphtho[2,1 -b]furan (10) in both vapour phase and liquid phase reactions. Compounds (3) and (10) react with 2,3-dimethylbut-2-ene on heating to give 4,5,6,7,8,9-hexafluoro-2-(2,2,3-trimethylbut-3-enyl)naphtho[2,1 -b]furan (16) and a small amount of 4,5,6,7,8,9-hexafluoro-2-(2,3,3-trimethylbut-1 -enyl)naphtho[2,1 -b]furan (15). Compound (10) reacts with 3,3-dimethylbut-1 -ene at 25 °C in the presence of BF₃–diethyl ether to give 2-(3,4-dimethylpent-3-enyl)-4,5,6,7,8,9-hexafluoronaphtho[2,1 -b]furan (19) and a small amount of (16). Both (3) and (10) on thermolysis with 3,3-dimethylbut-1 -ene give (16) and smaller amounts of (19) and (15), compounds (15) and (16) arising via reaction with 2,3-dimethylbut-2-ene formed by isomerisation of the terminal alkene. 2-Chloromethyl-4,5,6,7,8,9-hexafluoronaphtho[2,1 -b]furan (11) has been prepared; this reacts with 3,3-dimethylbut-1 -ene in the presence of ZnCl₂ to give (16), (15), and (19).