- PARTIALLY FLUORINATED HETEROCYCLIC COMPOUNDS. PART 17 . THE PREPARATION OF FUSED 2H-PYRAN DERIVATIVES FROM POLYFLUOROARYL AND -HETEROARYL PROP-2-ENYL ETHERS WITH POTASSIUM FLUORIDE VIA AN ELECTROCYCLISATION REACTION. A NOVEL SIGMATROPIC PROTON SHIFT DURING THE REACTION OF...
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A new synthesis of fused 2H-pyran derivatives via an electrocyclisation reaction is described which is based on a novel route to o-quinomethide-type precursors.These transient materials are formed by the dehydrofluorination (with KF) in dipolar aprotic solvents of the Claisen rearrangement intermediates produced by the thermolyses of polyfluoroaryl and -heteroaryl prop-2-enyl ethers. 5,6,7,8-Tetrafluoro-2H-1-benzopyran (4) is formed from the C6F5-ether (1) in refluxing DMF while 5,6,7,8,9,10-hexafluoro-2H-naphthopyran (6) is obtained from the 2-naphthyl ether (5) in sulpholane at 155-162 deg.The 2,4,5,6-tetrafluoro-3-pyridyl ether (8) in sulpholane at 182 deg gave a mixture of 6,7,8-trifluoro-2H-pyranopyridine (10) (34percent) and 5,6,8-trifluoro-2H-pyranopyridine (12) (1percent), but 2,3,5,6-tetrafluoropyridyl ether underwent dealkylation to the 4-hydroxypyridine.The o-quinodimethide intermediate from pentafluorophenylprop-2-enyl sulphide (13) isimerised via a novel sigmatropic proton shift before cyclisation to 4,5,6,7-tetrafluoro-2-methylbenzothiophen (14).
- Brooke, Gerald M.
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- Towards Weakly Coordinating Anions with the Extremely Electron Withdrawing Perfluoropyridinoxy Ligand –OC5F4N
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The extreme electron withdrawing properties of the perfluoropyridinoxy ligand –OC5F4N were used for the preparation of new (weakly) coordinating borate and aluminate anions of the type [E(OC5F4N)4]– (E = B or Al). These new anions are based on the potent parent Lewis acids E(OC5F4N)3, which possess exceptionally high calculated fluoride ion affinities (FIAs) of 500 and 587 kJ mol–1 for E = B and Al respectively. For aluminum, this extreme Lewis acidity dominates the chemistry and from mixtures of the neutral polymeric Lewis acid [Al(OC5F4N)3]n, the five- and six-coordinate complexes Al(OC5F4N)3(OEt2)2 (1) and [Al(OC5F4N)2(μ-OC5F4N) (NCMe)2]2 (2) were crystallized upon addition of ether or MeCN. The aluminate salts M[Al(OC5F4N)4] (M = Li or K) were prepared from the reaction between the alcohol 4-HO–C5F4N and either LiAlH4 or K[AlEt4] respectively. The aluminate anion [Al(OC5F4N)4]– remains Lewis acidic coordinating small donor molecules forming [Al(OC5F4N)4(L)]– (L = THF or NMe3) and even supports formation and structural characterisation of the aluminum dianion containing salt [Na(OEt2)2][Na][Al(OC5F4N)5] (8). The from NaBH4 and 4-HO–C5F4N accessible borate salt Na[B(OC5F4N)4] shows increased kinetic stability in comparison to the aluminum analogue.
- Riddlestone, Ian M.,Keller, Sarah,Kirschenmann, Florian,Schorpp, Marcel,Krossing, Ingo
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- Carboxylic Acid Deoxyfluorination and One-Pot Amide Bond Formation Using Pentafluoropyridine (PFP)
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This work describes the application of pentafluoropyridine (PFP), a cheap commercially available reagent, in the deoxyfluorination of carboxylic acids to acyl fluorides. The acyl fluorides can be formed from a range of acids under mild conditions. We also demonstrate that PFP can be utilized in a one-pot amide bond formation via in situ generation of acyl fluorides. This one-pot deoxyfluorination amide bond-forming reaction gives ready access to amides in yields of ≤94%.
- Brittain, William D. G.,Cobb, Steven L.
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supporting information
p. 5793 - 5798
(2021/08/01)
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- Catalytic defluorination of perfluorinated aromatics under oxidative conditions using N-bridged diiron phthalocyanine
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Carbon-fluorine bonds are the strongest single bonds in organic chemistry, making activation and cleavage usually associated with organometallic and reductive approaches particularly difficult. We describe here an efficient defluorination of poly- and perfluorinated aromatics under oxidative conditions catalyzed by the μ-nitrido diiron phthalocyanine complex [(Pc)Fe III(μ-N)FeIV(Pc)] under mild conditions (hydrogen peroxide as the oxidant, near-ambient temperatures). The reaction proceeds via the formation of a high-valent diiron phthalocyanine radical cation complex with fluoride axial ligands, [(Pc)(F)FeIV(μ-N)FeIV(F) (Pc+?)], which was isolated and characterized by UV-vis, EPR, 19F NMR, Fe K-edge EXAFS, XANES, and Kβ X-ray emission spectroscopy, ESI-MS, and electrochemical techniques. A wide range of per- and polyfluorinated aromatics (21 examples), including C6F6, C6F5CF3, C6F5CN, and C6F5NO2, were defluorinated with high conversions and high turnover numbers. [(Pc)FeIII(μ-N)Fe IV(Pc)] immobilized on a carbon support showed increased catalytic activity in heterogeneous defluorination in water, providing up to 4825 C-F cleavages per catalyst molecule. The μ-nitrido diiron structure is essential for the oxidative defluorination. Intramolecular competitive reactions using C6F3Cl3 and C6F3H 3 probes indicated preferential transformation of C-F bonds with respect to C-Cl and C-H bonds. On the basis of the available data, mechanistic issues of this unusual reactivity are discussed and a tentative mechanism of defluorination under oxidative conditions is proposed.
- Colomban, Cédric,Kudrik, Evgenij V.,Afanasiev, Pavel,Sorokin, Alexander B.
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supporting information
p. 11321 - 11330
(2014/11/07)
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- The ionic liquid [bmim]Br as an alternative medium for the catalytic cleavage of aromatic C-F and C-Cl bonds
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The potential of [bmim]Br as an alternative to aprotic dipolar solvents in nickel-catalyzed hydrodehalogenation reactions is demonstrated. Hydrodechlorination of pentafluorochlorobenzene proceeds under the action of zinc in aqueous [bmim]Br. Under the above conditions aromatic C-F bonds also undergo slow cleavage. The reaction is significantly accelerated in the presence of nickel complexes with 2,2′-bipyridine or 1,10-phenanthroline. In the case of pentafluoroacetanilide highly regioselective ortho-hydrodefluorination leading to the formation of 3,4,5-trifluoroacetanilide is observed.
- Prikhod'ko, Sergey A.,Adonin, Nicolay Yu.,Parmon, Valentin N.
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scheme or table
p. 2265 - 2268
(2010/05/18)
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- Process for the preparation of halogenated (meth)acrylic esters and poly (meth) arcylates obtained with said (meth)acrylic esters
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The present invention is directed to a process for the preparation of (meth)acrylates of halogenated alcohols by direct esterification of said alcohols with (meth)acrylic acid (chloride) wherein at least 2,6-substituted pyridine derivative is used as a po
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- Reaction of metal diethylnitroxides with pentafluoropyridine, pentafluorobenzene, octafluorotoluene and 2-chloro-3- or 5-nitropyridine
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Treatment of the nitroxides Et2NO(1-) M(1+) (2a-c) (M = Na, Li, K) and (Et2NO(1-))2Ba(2+) (2d) with pentafluoropyridine (3) at room temperature ( 1 d) gave in all cases the compounds Py-NEt2 (8), Py-ONEt2 (9), Py-NHEt (10) and Py-O(1-)H2NEt2(1+) (11) (where Py = tetrafluoro-4-pyridyl) in the approximate ratio 1:30:30:35.The radical traps, 1,4-dinitrobenzene or galvinoxyl, retarded the reaction (5 d required for complete consumption of 3), but the same products were formed in a similar ratio and compounds 8-11 were also formed by decomposition of the amine oxide Py-N(1+)O(1-)Et2 (20) 8 (57percent); 8 + (CF3CO)2O/H2O2 -> 20 (81percent) as the monohydrate>.It is proposed that the products 8-11 arose mainly via an SRN1 mechanism involving single electron transfer (SET) from the nitroxide 2 to the substrate 3 leading to the radical anion (21) and hence the tetrafluoro-4-pyridyl radical (22) which reacted with 2 at nitrogen to afford the amine oxide 20.Major Meisenheimer rearrangement of 20 gave hydroxylamine 9, while minor rearrangement afforded the hydroxylamine Py-N(Et)OEt (23) which eliminated ethanol to yield the secondary amine 10.Competing deoxygenation of 20 gave the tertiary amine 8 and the salt 11 was formed via decomposition of 8 in light (or on heating) involving homolytic fission of the weak N-O bond.Treatment of 9 with the acids AHF or CF3SO3H resulted in exothermic reaction and gave compounds 8 (27percent, 11percent), 10 (16percent, 18percent) and 11 (13percent, 25percent) via competing protonation at oxygen and nitrogen.The corresponding reactions of nitroxide 2a with the substrates C6HF5 (4) and C6F5CF3 (5) aforded the salt 4-H-C6F4-O(1-)H2NEt2(1+) (12) (15percent) and a mixture of the compounds 4-CF3-C6F4-R , respectively, while treatment of 2a with 2-chloro-3-nitropyridine (6) and 2-chloro-5-nitropyridine (7) gave the tertiary amines 2-N,N-diethylamino-3-nitropyridine (16) (35percent) or 2-N,N-diethylamino-5-nitropyridine (18) (25percent) together with N-(2-chloro-3-pyridyl)-N-(3-nitro-2-pyridyl)amine (17) (13percent) or N-(2-chloro-5-pyridyl)-N-(5-nitro-2-pyridyl)amine (19) (27percent) via presumed SRN1 pathways. - Keywords: Metal diethylnitroxides; Pentafluoropyridine; Pentafluorobenzene; Octafluorotoluene; 2-chloro-3-nitropyridine; 2-chloro-5-nitropyridine
- Admason, Adrian J.,Jondi, Waheed J.,Tipping, Anthony E.
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