An investigation into the thermolysts reactions of polyfluoroaromatic prop-2-ynyl ethers and thioethers

Abstract

This work investigates the thermal behaviour of polyfluoroaryl prop-2-ynyl ethers and thioethers in the vapour phase and solution phase. It also reports the thermolyses of 2-fluoromethyl-4,5,6,7,8,9-hexafluoronaphtho (2,1-b) furan (l6l) in the presence of 2,3-dimethylbut-2-ene and 3,3-dimethylbut-l-ene respectively. Chapter 1 discusses the history, mechanism and stereochemistry of the Glaisen and thio-Claisen rearrangements of aromatic prop-2-enyl and prop-2-ynyl systems. While Chapter 2, reports on the various cyclisation reactions that may follow an initial Glaisen rearrangement. Chapter 3 deals with the literature on the Glaisen and thio-Claisen rearrangements of polyfluoroaryl systems which are directly related to those under study in this thesis. Chapters 4 and 5 describe the isomerisation reactions of pentafluorophenyl prop-2-ynyl thioether (167) and 1,3,4,5,6,7,8-heptafluoro-2-naphthyl prop-2-ynyl thioether (171). Chapter 4 is concerned with the reaction of compound (167) with p-xylene and benzene at 180 C and in the presence of BF (_3)-etherate, at 25 C. Chapter 5 reports upon the reactions of the thioether (171) with benzene and p-xylene at l40 C and 160 C. At l60 G, in nickel apparatus the isomerisation product 2-fluoromethyl-4,5,6,7,8,9-hexafluoronaphtho (2,1-b) thiophen (173) is shown to be an intermediate in the conversion of the thioether (171) to the substitution product, 2-(2,5-dimethylbenzyl)-4,5,6,7,8,9-hexafluoronaphtho (2,1-b) thiophen (173) with p-xylene. This chapter also highlights the differing courses of reactions of the thioether (17l) in glass and nickel apparatus. Chapter 6 reports the isomerisation reactions of 1, 3, 4, 5, 6, 7, 8-heptafluoro-2-naphthyl prop-2-ynyl-ynyl ether (156) in both the liquid phase and vapour phase. The glass surface of the reaction vessel was shown to act as a Lewis-acid catalyst at elevated temperatures, in the reaction of the naphthyl ether (156) with p-xylene and isopropylbenzene to give the aromatic substitution products (159) and (160) respectively. Whereas in nickel apparatus, the 2-fluoromethyl compound (161) was the main product in both reactions. Chapter 7 discusses the mechanism of the isomerisation reactions of the polyfluoroaryl prop-2-ynyl ethers and thioethers studied in this thesis. It also incorporates a critical experiment in which compound (161) is reacted with N, N-diethylaniline at 140 C only to be recovered unchanged. (The thermolysis of (161) in p-xylene at the, same temperature gives the substitution product (159) exclusively) The charge-separated species (197) and (195) are proposed as intermediates in the reactions of the ether (156) and thioether (171) via the heterolytic fission of the sp (^3) C-F bond in the Claisen rearrangement intermediates (157) and (172) respectively. It is concluded that the isomerisation reactions of (I56) and (171), which require a 1, 4-fluorine shift, proceed via an ionic mechanism. The final chapter describes the thermolysis reactions of the naphthyl ether (156) and the 2-fluoromethyl compound (161) with 2, 3-dimethylbut-2-ene and 3, 3-dimethylbut-l-ene. Compounds (156) and (161) react with 2, 3-dimethylbut-2-ene at 150 C to give 2-(2,2,3-trimethylbut-3-enyl)-4,5,6,7,8,9-hexafluoronaphtho (2,1-b) furan (186) and a small amount of 2-(2,3,3-trlmethylbut-l.enyl)-4,5,6,7,8,9-hexafluoro-naphtho(2,1-b) furan (187) compound (161) reacts with 3,3-dimethylbut-l-ene at 25 C in the presence of BF(_3) -etherate to give the Markovnikov addition-elimination product, 2-(3,4-dimethylpent-3-enyl)-4,5,6,7,8,9-hexafluoro-naphtho (2,1-b) furan (194) and a small amount of (186). Thermolysis of both (156) and (161) with 3, 3-dimethylbut-1ene gave (186) as the major product accompanied by smaller amounts of (187) and (194). It is proposed that compounds (186) and (187) arise 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,l-b) furan (161a) has been prepared; it reacts with 3,3-dimethylbut-l-ene in the presence of ZnCl (_2), to give (186), (194) and (196).