- Synthesis and Properties of N-Fluoropyridinium Salts
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Various stable N-fluoropyridinium salts with a non- or weakly nucleophilic counter anion such as TfO-, FSO3-, BF4-, ClO4-, CH3SO3- etc., or with an electron-donating or -withdrawing substituent(s) on the pyridine ring were synthesized and their properties investigated.N-Fluoropyridinium-2-sulfonates, N-fluoroquinolinium triflate, and highly hindered N-fluoro-2,6-di-t-butylpyridinium salts were also synthesized.They were synthesized by counter anion displacement reactions of unstable pyridine-F2 conpounds, fluorination of salts of pyridines with protonic acids or silyl esters with F2, and/or fluorination of Lewis acid complexes of pyridines.The scope of each method was examined in detail.Each of the N-fluoropyridinium salts was assigned as the first stable 1:1 salt structure of the pyridine nucleus and halogen atom on the basis of the spectral and elemental analysis.The stability depended on the nucleophilicity or basicity of the counter anions and electronic nature or position of the ring substituents.These results and NMR analyses clearly showed the unstable pyridine-F2 compounds to have N-fluoropyridinium fluoride salt structure.Some N-fluoropyridinium triflates were hydrolyzed and the products were examined, suggesting a unique hydrolysis mechanism.
- Umemoto, Teruo,Harasawa, Kikuko,Tomizawa, Ginjiro,Kawada, Kosuke,Tomita, Kyoichi
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p. 1081 - 1092
(2007/10/02)
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- N-fluorination with cesium fluoroxysulfate
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Cesium fluoroxysulfate was proved to be a N-fluorinating agent for some nitrogen compounds. Yields of products obtained, mainly monofluoro-derivatives, depend on structures of initial nitrogen compounds. The ability of cesium fluoroxysylfate for N-fluorin
- Gakh,Romaniko,Ugrak,Fainzilberg
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p. 7447 - 7458
(2007/10/02)
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- Preparation of 2-Fluoropyridines via Base-Induced Decomposition of N-Fluoropyridinium Salts
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N-Fluoropyridinium salts with either BF4-, SbF6-, or PF6- as a counteranion were treated with excess base such as triethylamine at room temperature to give 2-fluoropyridine in good yield.This method was succesfully applied to the preparation of 2-fluoropyridine derivatives possessing electron-donating or -withdrawing substituents using substituted N-fluoropyridinium tetrafluoroborates.Pyridine-F2 compounds produced through reactions of pyridines with molecular fluorine were also treated with base to give 2-fluoropyridines but in low yields.These reactions are considered to occur through a carbene mechanism as follows: a novel N-F-containing cyclic carbene (3), generated from the N-fluoropyridinium salts by 2-proton abstraction, reacts with fluorine atoms from counteranions such as BF4-, SbF6-, or PF6-, followed by elimination of F- from the N-F moiety, to yield 2-fluoropyridines.Previously reported findings in reactions of pyridines with molecular fluorine are explained on the basis of this mechanism.
- Umemoto, Teruo,Tomizawa, Ginjiro
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p. 1726 - 1731
(2007/10/02)
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- N-FLUOROPYRIDINIUM TRIFLATE AND ITS ANALOGS, THE FIRST STABLE 1:1 SALTS OF PYRIDINE NUCLEUS AND HALOGEN ATOM
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N-Fluoropyridinium salts having non-nucleophilic counter-anions and their derivatives were synthesized by treating pyridine-F2 adducts with strong Broensted acids, their salts or trimethylsilyl esters, of Lewis acids, or by allowing F2 to react with N-trimethylsilylpyridinium salts.
- Umemoto, Teruo,Tomita, Kyoichi
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p. 3271 - 3274
(2007/10/02)
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