Michael G. Barlow

Preparation of 2,3,3,3-tetrafluoropropene from trifluoroacetylacetone and sulphur tetrafluoride

Abstract Practical details are presented for the laboratory preparation of 2,3,3,3-tetrafluoropropene in good yield from trifluoroacetylacetone and sulphur tetrafluoride in the presence of hydrogen fluoride. The gas-phase IR spectrum of the tetrafluoropropene (b.p., −28 °C) is reproduced and a detailed analysis of the olefins nuclear magnetic resonance (NMR) spectra (1H, 13C, 19F) is provided.

A high-yield synthesis of 3-carboethoxy-4-trifluoromethylfuran and some Diels-Alder reactions of this furoate with acetylenic dienophiles

Abstract The reaction of furan with ethyl 4,4,4-trifluorobut-2-ynoate (1) (1.2:1 molar ratio) in vacuo at 40 °C gives the 1:1 adduct oxanorbornadiene (3) (70%) and the 2:1 adduct (5) as the endo,exo (5a) (16%) and exo,exo (5b) (10%) isomers; at 20 °C, using an excess of ester 1, the yield of 1:1 adduct 3 is increased to 93%. Catalytic hydrogenation ( Pd C/Me 2 CO ) of1:1 adduct 3 with control of the hydrogen uptake affords either the oxanorbornane 9 (89%) or the oxanorbornene 10 (90%), and flow pyrolysis of compound 10 at 400 °C in nitrogen gives 3-carboethoxy-4-trifluoromethylfuran (2) (89%). Diels-Alder cycloaddition reactions of furan 2 with the alkynes CF3CCCF3 (100 °C), 1 (100 °C) and MeO2CCCCO2Me (120 °C) in solvent CH2Cl2 afford the 1:1 adducts 13 (95%), 14 (47%) plus 15 (45%), and 16 (92%), respectively, but reaction with ethyl propynoate does not take place at or below 120 °C and at 150 °C a complex product mixture is obtained. The 1:1 adduct 3 undergoes reaction with triflic acid in solvent CH2Cl2 heated under reflux to give 2-carboethoxy-3-trifluoromethylphenol (23) (31%) and 3-carboethoxy-2-trifluoromethylphenol (24) (48%) and with concentrated sulfuric acid under the same conditions to afford phenols 23 (21%) and 24 (32%), but the oxanorbornadiene 13 does not undergo reaction with triflic acid at temperatures up to 80 °C.

The preparation and some reactions of 2,5-dichloro-1,1,1,6,6,6-hexafluoro-3,4-diazahexa-2,4-diene

Abstract The title azine(I) can be conveniently prepared by treatment of 1,2-bistrifluoroacetylhydrazine with NN - dimethylaniline hydrochloride in phosphoryl chloride at ca . 100 °C. It undergoes facile displacement of one or both chlorine atoms on treatment with a variety of nitrogen-, oxygen- and sulphur-centred nucleophiles as well as with iodide and fluoride ions. The bisanilino-substituted azine (Vd) is thermally unstable and cyclises with elimination of aniline to the triazole (Vla), while the perfluoroazine (Vj) undergoes cycloaddition with acetylene.

Fluorocarbon derivatives of nitrogen. Part IV [1]. Perfluoro-1-azacyclohex-1-ylcaesium

Abstract Caesium fluoride combined with perfluoro-1-azacyclohexene in acetonitrile to yield perfluoro-1-azacyclohex-1-ylcaesium (1), which was characterised by 19 F n.m.r. spectroscopy and by treatment with iodomethane to give 2,2,3,3,4,4,5,5,6,6-decafluoro-1-methyl-1-azacyclohexane (2). Attempts to derivatize the caesium salt with chlorotrimethylsilane provided fluorotrimethylsilane, perfluoro-[1-(1-azacyclohex-1-en-2-yl)-1-azacyclohexane] (4), and 2-chloro-3,3,4,4,5,5,6,6-octafluoro-1-azacyclohexene (5); information on the course of this reaction was obtained through experiments in which perfluoro-1-azacyclohexene was shown to undergo conversion into its chloro-analogue (5) and its dimer (4) via treatment with chlorotrimethylsilane and fluoride ion, respectively. Aluminium chloride also converts perfluoro-1-azacyclohexene into its chloro-analogue (5).

Diels–Alder reactions of trichloro-1,2,4-triazine: intramolecular additions with 1,5 and 1,6 dienes

Trichloro-1,2,4-triazine reacts with cycloheptene and cyclododecene to give the 2,6-dichloropyridine derivatives 6 and 7 via an intermediate dihydropyridine formed by Diels–Alder addition and loss of N2, and with cyclopenta-1,3-diene and indene by addition of a second molecule of alkene to the intermediate dihydropyridine. Bicyclo [2.2.1]hepta-2,5-diene and quadricyclane give mainly 2,3,6-trichloropyridine by loss of cyclopentadiene from the intermediate dihydropyridine. With hexa-1,5-diene, the dihydropyridine is trapped by an intramolecular Diels–Alder reaction, forming tricyclic compounds 17 and 18. With diallyl ether, the dihydropyridine partly undergoes intramolecular cycloaddition to give 23 and partly [1,5]-sigmatropic shift of hydrogen before intramolecular cycloaddition to give 25. With cyclododeca-1,5,9-triene formation of pyridine derivatives is incomplete and the immediate precursor can be trapped with water.

Heterocyclic polyfluoro-compounds. Part 37. Diels–Alder reactions of trichloro- and trifluoro-1,2,4-triazine

Trichloro-1,2,4-triazine undergoes reaction at 70 °C with the olefins: ethylene, (Z)-but-2-ene, cyclopentene, and (Z)-cyclo-octene to give the 3,4-substituted 2,6-dichloropyridine derivatives, 3,4-R2C5HCl2N, where R2= H2(1%), Me2(75%), (CH2)3(77%), and (CH2)6(80%), respectively, in a reaction which appears to involve initial Diels–Alder addition, and loss of nitrogen, to form an intermediate dihydropyridine. This dihydropyridine then undergoes a [1,5] sigmatropic hydrogen shift and loss of hydrogen chloride to give the pyridine, but adds a second molecule of cyclopentene to the extent of 3% in a further Diels–Alder reaction, and this is the sole pathway with bicyclo [2.21] hept-2-ene.With trifluoro-1,2,4-triazine and the olefins cyclopentene, (Z)-cyclo-octene, and bicyclo[2.2.1]hept-2-ene, only products derived by addition of a second molecule of olefin to an intermediate dihydropyridine are obtained in 55, 13, and 52% yield respectively. Bis(trimethylstannyl)acetylene gives 3,4-bis(trimethylstannyl)-2,5,6-trifluoropyridine (11%), and bicyclo[2.2.1]hepta-2,5-diene gives 2,3,6-trifluoropyridine (43%).

Diels–Alder reactions of trichloro- and trifluoro-1,2,4-triazine

Diels–Alder addition of olefins to trichloro- and trifluoro-1,2,4-triazines gives, via loss of nitrogen, intermediate dihydropyridines, which undergo a variety of further pericyclic reactions.

Valence-bond isomer chemistry—IX: Thermal and photochemical formation of valence-bond isomers of perfluoro-pentaethylmethylbenzene and -1,2,3,5-tetraethyl-4,6-dimethylbenzene

Abstract Perfluoropentaethylmethylbenzene is thermally (425–600°) or photochemically (λ > 270 nm) isomerised to a mixture of perfluoro - 1,2,3,5,6 - pentaethyl - 4 - methyl - and possibly perfluoro - 1,2,3,4,5 - pentaethyl - 6 - methyl - bicyclo[2.2.0]hexa - 2,5 - dienes. Perfluoropentaethylmethyltetracyclo[2.2.0 2,6 .0 3,5 ]hexane is formed when shorter wavelength light (λ > 200 nm) is used. Similarly, perfluoro - 1,2,3,5 - tetraethyl - 4,6 - dimethylbenzene is thermally isomerised (500°) to a mixture of perfluoro - 1,2,3,5 - tetraethyl - 4,6 - dimethyl - and possibly perfluoro - 1,2,4,6 - tetraethyl - 3,5 - dimethylbicyclo [2.2.0]hexa - 2,5 - dienes. The valence-bond isomers have notable thermal stability.

Fluorinated acetylenes. Part 15. The reaction of ethyl 4,4,4-trifluorobut-2-ynoate with dienes and cycloheptatriene☆

Abstract Thermal reaction of the acetylenic ester CF3CCCO2Et (1) with cyclopentadiene (4), buta-1,3-diene (5) and 1,4-diphenylbuta-1,3-diene (6) gave the corresponding Diels-Alder 1:1 cycloadducts 10, 11 and 12, respectively in high yield (73%–97%). With norbornadiene (7), the homo Diels-Alder adduct (13) was formed. The reaction with 3-carboethoxyfuran gave a mixture (55%) of the isomeric Diels-Alder 1:1 adducts 14 and 15 (ratio 55:45), together with four 2:1 adducts, i.e., the exo,endo compounds 16a (10%) and 16b (9%) and the exo,exo compounds 17a (8%) and 17b (9%), resulting from Diels-Alder cycloaddition of the furan to the least substituted double bond in the 1:1 adducts 14 and 15. The cycloadditions to the 1:1 adducts were regioselective with the two CO2Et groups on the unsaturated bonds involved in the cycloadditions being 1,4 to each other in the 2:1 adducts. The products from reaction of ester 1 with cycloheptatriene (9) were formed via two competing reaction paths; (a) cycloaddition of ester 1 to norcaradiene (23) which gave the Diels-Alder adduct 18 (74%) and (b) an initial regioselective ‘ene’ reaction followed by isomerisation of the resulting 1:1 adduct 24 to the corresponding norcaradiene 25, which then underwent both rearrangement to afford 1:1 adduct 19 (15%) and Diels-Alder cycloaddition with ester 1 to give the 2:1 adduct 20 (6%).

Fluorinated acetylenes. Part 13 [1]. Synthesis of 1,6-diphenyl-3,3,4,4-tetrafluorohexa-1,5-diyne

Abstract The title compound ( 6 ) may be conveniently synthesised via the three-stage route: In the first stage the alkyne PhCCBr is also produced, and this undergoes reactionwith iodine generated in the second stage to give the alkene ( E )-PhCI=CBrI ( 10 ) (upto 9.5%). Other by-products formed in the second stage, depending on the conditionsemployed, are the 1,4-diyne PhCCCF 2 CCPh ( 12 ), isolated in 3.5% yield, and l-iodo-2,3-naphtho-4-phenyltetrafluorocyclobutene ( 11 ), isolated in 11.5% yield. Mechanismsare advanced to account for all the products isolated.