Synthesis of new α,α,β,β-tetrafluoroesters

Substituted phenyl iodides or diiodides reacted with ethyl iodotetrafluoroproponylate ICF₂CF₂CO₂Et, 1 in the presence of copper powder to give the coupled products 2 or 3 in good yields. Addition of 1 to ethylene and allyl acetate proceeded smoothly under thermal and radical conditions to give the corresponding adducts, which underwent elimination reaction to give β-vinyl and β-allyl α,α,β,β-tetrafluoroesters, CH₂CHCF₂CF₂CO₂Et, 4 and CH₂CHCH₂CF₂CF₂CO₂Et, 5, respectively. 1 also readily reacted with 1,5-hexadiene and 1-hexene with copper or palladium complex, followed by reduction to remove iodine to produce ω-alkenyl-α,α,β,β-tetrafluoroester CH₂CH(CH₂)₄CF₂CF₂CO₂Et 6 and α,α,β,β-tetrafluoroester C₄H₉CH₂CHICF₂CF₂CO₂Et.     

Initiating radical cyclizations by H transfer from transition metals

CpCr(CO)₃H and HV(CO)₄(P-P) (where P-P is a chelating diphosphine) can be used to initiate radical cyclizations by transferring H to activated terminal olefins. CpCr(CO)₃H can catalyze reductive cyclizations, with H₂ as the ultimate reductant. Appropriate substrates can be assembled by the Morita-Baylis-Hillman reaction of methyl acrylate with an aldehyde. Six- as well as five-membered rings can be formed, and a tandem cyclization to decalin can be effected.     

Reaction of CF3 radicals with H2S

Hydrogen abstration from H₂S by CF₃ radicals, generated by the photolysis of both CF₃COCF₃ and CF₃I, has been studied in the temperature range 314–434 K. The rate constant, based on the value of 10^13.36 cm³/mol · s for the recombination of CF₃ radicals, is given by with CF₃COCF₃ as the radical source, and with CF₃I as the radical source, where k₂ is in cm³/mol · s and E is in J/mol. These results resolve a previously existing controversy concerning the values of the rate constants for this reaction. They show that CF₃ radicals are less reactive than CH₃ radicals in attacking H₂S, and this behavior indicates that polar effects play a significant role in the hydrogen transfer reactions of CF₃ radicals.     

Synthesis of perfluoro-t-butyl trifluorovinyl ether and its copolymerization with TFE

Perfluoro-t-butyl trifluorovinyl ether (CF₃)₃COCFCF₂ was prepared by the addition of perfluoro-t-butyl hypofluorite (CF₃)₃COF to 1,2-dichloro-1,2-difluoroethylene followed by dechlorination. The obtained trifluorovinyl ether monomer readily copolymerizes with TFE in the presence of a radical initiator.     

Pd-catalyzed asymmetric Wacker-type cyclization of o-trisubstituted allylphenols by use of tetraoxazoline ligands

Pd(II)-catalyzed intramolecular Wacker-type cyclizations of o-trisubstituted allylphenols were studied. The chelation-induced axially chiral catalytic system, Pd(CF₃COO)₂-8 (1:1 molar ratio), showed excellent catalytic activities and enantioselectivities in the Wacker-type cyclizations of o-trisubstituted allylphenols with up to 94% ee.     

Reactions of quadricyclane with fluorinated nitrogen-containing compounds. Synthesis of 3-aza-4-perfluoroalkyl-tricyclo[4.2.1.0]non-3,7-dienes

The cycloaddition reactions of quadricyclane (1) and polyfluorinated imines and nitriles were studied. Both (CF₃)₂CNH and (CF₃)₂CN(2-FC₆H₄) were found to have low reactivity towards 1, giving the corresponding [2 + 2 + 2] cycloadducts in a low yield. C₂F₅NCFCF₃ however, reacts with 1 rapidly, giving a mixture of two isomeric cycloadducts in a high yield. Perfluoroalkyl nitriles R_fCN (R_f = CF₃, C₂F₅, n-C₃F₇) were found to have surprisingly high reactivity to 1 producing exo-3-aza-4-(fluoroalkyl)-tricyclo[4.2.1.0^2,5]non-3,7-dienes in 56-81% yields at elevated temperature. Exo-3-aza-4-(perfluoroalkyl)-tricyclo[4.2.1.0^2,5]non-3,7-dienes rapidly react with CF₃Si(CH₃)₃ in the presence of CsF catalyst. The reaction results in addition of CF₃Si(CH₃)₃ across the CN bond of the azadienes with selective formation of only one stereoisomer of exo-3-aza-3-(trimethylsilyl)-4,4-bis(perfluoroalkyl)-tricyclo[4.2.1.0^2,5]non-7-enes. Silyl group in this compounds can be removed either by the action of tetrabutylammonium fluoride hydrate, leading to the formation of the corresponding amine after hydrolysis, or by reaction with HCl resulting in the formation of the corresponding amine hydrochloride.     

Lewis acid catalyzed heavy atom tunneling – the case of 1H-bicyclo[3.1.0]-hexa-3,5-dien-2-one

For many thermal reactions, the effects of catalysis or the influence of solvents on reaction rates can be rationalized by simple transition state models. This is not the case for reactions controlled by quantum tunneling, which do not proceed via transition states, and therefore lack the simple concept of transition state stabilization. 1H-Bicyclo[3.1.0]-hexa-3,5-dien-2-one is a highly strained cyclopropene that rearranges to 4-oxocyclohexa-2,5-dienylidene via heavy-atom tunneling. H₂O, CF₃I, or BF₃ form Lewis acid–base complexes with both reactant and product, and the influence of these intermolecular complexes on the tunneling rates for this rearrangement was studied. The tunneling rate increases by a factor of 11 for the H₂O complex, by 23 for the CF₃I complex, and is too fast to be measured for the BF₃ complex. These observations agree with quantum chemical calculations predicting a decrease in both barrier height and barrier width upon complexation with Lewis acids, resulting in the observed Lewis acid catalysis of the tunneling rearrangement.

The ring-opening of a highly strained cyclopropene to a carbene proceeds via heavy-atom tunneling. This rearrangement is accelerated in the presence of H₂O, ICF₃ or BF₃, resulting in a novel Lewis-acid catalyzed tunneling reaction.     

Formation of bromodifluoroacetyl fluoride, CF2BrC(O)F, in the thermal gas-phase oxidation of bromotrifluoroethene, CF2CFBr, initiated by trifluoromethylhypofluorite, CF3OF

The oxidation of CF₂CFBr by molecular O₂, initiated by CF₃OF, has been studied at 273, 253.5, 239 and 218 K. The initial pressure of CF₃OF was varied between 0.9 and 2.4 Torr, that of CF₂CFBr between 11.5 and 30.7 Torr and that of O₂ between 42.5 and 100.7 Torr. The main product was CF₂BrC(O)F (yields 81-95% based on the CF₂CFBr consumed). Minor amounts of C(O)F₂ and C(O)FBr and traces of bromotrifluoroethene epoxide were also formed. The reaction is a chain reaction with bromine atoms as chain carriers. Its basic steps are: the thermal generation of CF₃O radical by abstraction of fluorine atom from CF₃OF, chain initiation by addition of CF₃O to the double bond of alkene, leading, in presence of O₂, to the formation of bromine atom and chain propagation by the reaction of bromine atom with CF₂CFBr, originating CF₂BrCFBrO radical. The predominant fate of the latter is the bromine atom extrusion with CC bond scission playing the minor role. The full mechanism is postulated.     

Hydrogen bonding and halogen bonding co-existing in the reaction of heptafluorobenzyl iodide with N,N,N,N-tetramethylethylene diamine

Two novel assembling systems 3 and 4, with the structures of C₆F₅CF₂⁻?H⁺N(Me)₂CH₂CH₂(Me₂)N⁺H?⁻CF₂C₆F₅ and C₆F₅CF₂I?N(Me)₂CH₂CH₂(Me)₂N?ICF₂C₆F₅, respectively, have been generated from the solution of heptafluorobenzyl iodide 1 and N,N,N^′,N^′-tetramethylethylenediamine 2 in dichloromethane. Their structures have been characterized by X-ray diffraction analysis, NMR and IR spectroscopy. Intermolecular N?I halogen bond and F?H hydrogen bond are revealed to be the driving forces for their formation.     

Iodine fluorosulfate reactions with fluorocarbons

Iodine monofluorosulfate has been found to react with fluoroolefins in the absence of a solvent to give the corresponding iodo alkyl fluorosulfates by addition of ?l and ?OSO₂F across the double bond. The observed products were ICF₂CF₂SO₃F, CF₃CFlCF₂SO₃F, and the isomer mixture ICF₂CFClSO₃F and ICFClCF₂SO₃F. Perfluorocyclobutene was unreactive. The iodine fluorosulfate used for this study was synthesized from the reactions of either I₂ or R_fI with ClSO₃F, with both reactions being new routes to this compound. These iodo fluorocarbon fluorosulfates are novel compounds and were characterized by spectroscopy and by formation of the derivatives CF₃CFICFO and ICF₂CFO.     

Carbon-carbon bond formation by radical addition of α-trifluoromethylacrylate with cyclic ethers

The radical addition reactivity of tert-butyl α-trifluoromethylacrylate (CH₂C(CF₃)COOC(CH₃)₃) (BFMA) with cyclic ethers was investigated in order to compare to that of perfluoroisopropenyl ester. One to one addition compound of BFMA with tetrahydrofuran (THF) was produced in fairy high yields in the presence of 2,2′-azobisisobutyronitrile, benzoyl peroxide or di-tert-butyl peroxide to give 2-substituted THF derivative. Time-conversion investigation showed much higher reactivity of BFMA compared to that of 2-benzoxypentafluoropropene [CF₂C(CF₃)OCOC₆H₅]. Radical additions of BFMA with 1,4-dioxane, 1,3-dioxolane and tetrahydropyran were also examined to afford corresponding 1:1 addition products in fairly high yields by achieving carbon-carbon bond formation. It is then concluded that no interconversion of fluoroalkylcarbon radical and hydrocarbon radical may take place in the reaction system of BFMA which possesses two less fluorines in the vinyl group compared to 2-benzoxypentafluoropropene. The method may be a facile way to prepare trifluoromethyl-substituted organic compounds accompanied by the formation of carbon-carbon bonds by the aid of fluorine atoms.     

Investigation of the structure and reactivity of the stable perfluorodiisopropylethylmethyl radical by ESR and molecular mechanics

The hyperfine coupling (HFC) constants of the unpaired electron with the fluorine nuclei in the stable radical [(CF₃)₂CF]₂CF₂CF₃ (II) were determined by ESR. The stable conformation and the barriers to rotation of the substituents in this radical were calculated by molecular mechanics. The results were consistent with the ESR data. The kinetics of the destruction of the radical (II) were investigated, and the kinetic parameters of the dissociation were determined (k₁₄₀=4.6·10^–4 sec^–1, E_act=30±5 kcal/mole). The disappearance of the radical (II) is accompanied by the accumulation of the new radical (CF₃)₂CF(CF₃)CF(CF₃)CF₂CF₃ (IV), which was studied by ESR. Heating of (II) in the presence of electron donors leads to the partly reversible reduction of the radical (II).Translated from Izvestiva Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1507–1512, July, 1991.     

Tandem radical cyclization-based strategy for the synthesis of oxa- and aza-cages: a case of fragmentation versus cyclization

A new strategy for the synthesis of oxa- and aza-cage compounds based on tandem radical cyclizations is described. The iodides 1 lead to oxa-cages 3 after two tandem radical cyclizations. The ester 10aa on reaction with n-Bu₃SnH and AIBN gives rise to the oxa-cage 12aa after two tandem 5-exo-trig cyclizations. On the other hand, reaction of the ketones 17aa and 21 under similar conditions furnished the oxa-cages 20aa and 23, respectively, via a double 5-exo-trig tandem radical cyclization followed by fragmentation.     

EPR studies on regio-selective H-abstraction by “magic blue” reagent from polymers

The radical reactions of polyolefin and olefin copolymers (4-9), polydienes and diene coplymers (10-15), and polysiloxane (16) with “magic blue” reagent containing H-abstracting agent-bis{perfluoro-1-[1-(2-fluorosulfonyl)ethoxy]ethyl}nitroxide [FSO₂CF₂CF₂OCF(CF₃)]₂N(O) (2)and spin trap-perfluoro-1-nitroso-[1-(2-fluoro-sulfonyl)ethoxy]ethane FSO₂CF₂CF₂OCF(CF₃)NO (3) were studied by EPR detection of the spin adducts of the corresponding polymeric radicals generated in the H-abstraction step to the spin trap 3, namely, the nitroxides FSO₂CF₂CF₂OCF(CF₃)N(O) (polymer-H) 17-29. EPR studies have provided information about the regio-selectivity of H-abstraction, the subsequent radical steps followed H-abstraction and grounded a possibility of employing “magic blue” reagent in polymer modification via H-abstraction-initiated grafting polymerization.     

Study of the Gas-Phase Intramolecular Aryltrifluoromethylation of Phenyl(Trifluoromethyl)Iodonium by ESI-MS/MS

The gas-phase reactions of the reactive λ ³-phenyl(trifluoromethyl)iodonium (PhI⁺(III)CF₃, 1 at m/z 273) to the radical cation of iodobenzene (PhI^?+, 2 at m/z 204) via the loss of ·CF₃ and the radical cation of trifluoromethylbenzene (PhCF₃ ^?+, 3 at m/z 146) via the loss of ·I, were studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS). Interestingly, the gas-phase intramolecular coupling reaction of CF₃ with phenyl via the CF₃ migration process of 1 at m/z 273 from iodine to the phenyl to give 3 at m/z 146 could only occur according to an intramolecular aromatic substitution mechanism. Density functional theory (DFT) calculations showed that the gas-phase intramolecular aryltrifluoromethylation of 1 at m/z 273 to 3 at m/z 146 occurred via a Meisenheimer complex intermediate (MC), where the triplevalent I center of 1 was reduced to monovalent I. Most importantly, the structure of 3 at m/z 146 derived from 1 at m/z 273 in ESI-MS/MS process was confirmed by comparison of its MS/MS with that of an authentic PhCF₃ ^?+ at m/z 146 acquired from the electron ionization (EI)-MS/MS analysis of PhCF₃. Thus, our studies revealed the intrinsic reactivity tendencies of λ³-phenyl(trifluoromethyl)iodonium under solvent-free conditions.      

Atmospheric chemistry of CF3CFCH2: Products and mechanisms of Cl atom and OH radical initiated oxidation

The products of Cl atom and OH radical initiated oxidation of CF₃CFCH₂ were studied in 700 Torr of N₂/O₂ diluent at 296 ± 1 K. The reactions of Cl atoms and OH radicals with CF₃CFCH₂ proceed via electrophilic addition to the double bond. The reaction with chlorine atoms proceeds 56 ± 5% via addition to the central carbon. The chlorine atom initiated oxidation of CF₃CFCH₂ gives CF₃C(O)F in a molar yield which is indistinguishable from 100% and independent of [O₂], and HC(O)Cl in a molar yield which increased from 30% to 59% as [O₂] was increased from 3 to 700 Torr. The OH radical initiated oxidation of CF₃CFCH₂ gives CF₃C(O)F as major product in a yield of 91 ± 6%. The results are discussed with respect to the atmospheric chemistry and environmental impact of CF₃CFCH₂.     

EPR studies on H-abstraction from p-substituted benzaldehydes by new “Magic Blue” reagents and correlation analysis of aN values of ω-fluorosulfonylperfluoroalkyl p-substituted benzoyl nitroxides

New “Magic Blue” reagent, namely, the blue solution in F113 (CClF₂CCl₂F) containing H-abstracting agent bis[ω-fluorosulfonylperfluoroalkyl] nitroxide R_FN(O)R_F2 and ω-fluorosulfonylperfluoronitrosoalkane spin trap R_FNO 3 both generated in the reaction of ω-fluorosulfonylperfluorodiacyl peroxide [FO₂SCF₂CF₂OCF(CF₃)CF₂OCF(CF₃)COO]₂1 with sodium nitrite in F113 (CClF₂CCl₂F) at room temperature, reacted with a series of p-substituted benzaldehydes 4 via regio-selective abstraction of the formyl hydrogen followed by spin trapping of the acyl radical intermediate 5, thus led to the formation of stable spin adducts ω-fluorosulfonylperfluoroalkyl p-substituted benzoyl nitroxides 6. The correlation analyses of a_N values of nitroxides 6 with various substituent constants disclose that the polar effects are the major factors varying the spin density on the nitroxyl-nitrogen while the effect through spin-delocalization is felt slightly.     

Reasons for Selective C–C Bond Rupture upon Photodegradation of the Long-Lived Perfluoro-2,4-dimethyl-3-ethylpentyl-3 Radical

A difference in the mechanisms of photoinduced and thermal decomposition of [(CF₃)₂CF]₂C · C₂F₅ radical was demonstrated on the basis of comparison of experimental results and quantum-chemical calculation data. Irradiation with light of < 320 nm resulted in transition of the radical to an excited state followed by the rupture of the CF₂–CF₃ bond having the greatest length in the ground state. In the thermal degradation of this radical (heating up to 373 K), the rupture >CF–CF₃ bonds is more favorable because of low activation barriers for the process (42–54 kJ/mol). The CF₂–CF₃ bond rupture during thermolysis is unlikely, since the corresponding activation barrier is as high as 84–109 kJ/mol.