- 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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- Method for preparing N-fluoropyridinium salt
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N-fluoropyridinium salts of the following formula are prepared by reacting a pyridine compound with a Br nsted acid and fluorine, wherein the reaction solvent contains a greater than equimolar amount of the pyridine compound relative to an amount of the Br nsted acid. STR1 The method can produce N-fluoropyridinium salts with a high yield.
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- N-fluoropyridinium salt and process for preparing same
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A pyridine-compound is reacted with fluorine together with a Bronsted acid-compound or Lewis acid to form a N-fluoropyridinium salt which is very active to other compounds but is very selective for the preparation of a desired product and this product is very useful for a fluorine-introducing agent which makes it useful for the preparation of fluoro-compounds such as thyroid inhibitor.
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- 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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- 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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