- A Novel Convenient Synthesis of Pyridinyl and Quinolinyl Triflates and Tosylates via One-Pot Diazotization of Aminopyridines and Aminoquinolines in Solution
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The first effective and simple method for the direct one-pot transformation of 2-, 3-, and 4-aminopyridines, 2,6-diaminopyridines, and 2-aminoquinoline into the corresponding pyridinyl and quinolinyl trifluoromethanesulfonates and tosylates in solvents was developed. The procedure involves diazotization of the heterocyclic amines with sodium nitrite in mixed hexane-DMSO or hexane-DMF solutions in the presence of trifluoromethanesulfonic acid or p-toluenesulfonic acid.
- Kassanova, Assiya Zh.,Krasnokutskaya, Elena A.,Beisembai, Perizat S.,Filimonov, Victor D.
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p. 256 - 262
(2016/01/15)
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- Novel base-initiated reactions of N-substituted pyridinium salts
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Reaction of N-fluoropyridinium triflate with a base in dichloromethane gave 2-chloropyridine as the major product along with 2-pyridyl triflate and 2-fluoropyridine, regardless of the nature of the base. This base-initiated reaction was also shown to take place similarly in other halogenated alkanes, ethers, a nitrile, aromatics, a ketone, vinyl ethers, alcohols and trimethylsilyl acetate as solvents to give pyridine derivatives substituted with a solvent molecule (s) at the 2-position. N-(Trifluoromethanesulfonyloxy)-and (benzenesulfonyloxy) pyridinium salts were found to undergo the same base-initiated reaction. These reactions may be explained by a postulated singlet carbene (canonical formula 11b) produced through proton abstraction of N-substituted pyridinium salts. A similar carbene reaction may thus likely occur in the thermal decomposition of thiatriazole 10. Ab initio MO calculations revealed the structure and properties of the labile deprotonated N-fluoropyridinium cation and supported the carbene intermediate reaction mechanism rather than a pyridynium or pyridyl cation mechanism. Quarroz's reports on the reactions of picolinic acid N-oxide and the reported reactions of pyridines with F2, CH3COOF or CsSO4F in solvents may be explained by this carbene mechanism.
- Umemoto, Teruo,Tomizawa, Ginjiro,Hachisuka, Hitoharu,Kitano, Masakatsu
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p. 161 - 168
(2007/10/03)
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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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- BASE-INITIATED REACTIONS OF N-FLUOROPYRIDINIUM SALTS; A NOVEL CYCLIC CARBENE PROPOSED AS A REACTIVE SPECIES
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A new type of base-initiated reactions of pyridinium salts was found and a novel cyclic carbene was proposed as the reactive species.
- Unemoto, Teruo,Tomizawa, Ginjiro
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p. 2705 - 2708
(2007/10/02)
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