- Synthesis of: Meta -substituted [18F]3-fluoro-4-aminopyridine via direct radiofluorination of pyridine N -oxides
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Due to their electron-rich aromatic structure, nucleophilic (radio)fluorination of pyridines is challenging, especially at the meta position. In this paper, we describe the first example of direct fluorination of a pyridine N-oxide to produce a meta fluorinated pyridine. Specifically, fluorination of 3-bromo-4-nitropyridine N-oxide produced in several minutes 3-fluoro-4-nitropyridine N-oxide in moderate yield at room temperature. This intermediate compound was later converted to 3-fluoro-4-aminopyridine easily by catalytic hydrogenation. Furthermore, this approach was successfully applied for labeling with fluorine-18. The use of pyridine N-oxides for the preparation of fluoropyridines is unprecedented in the chemical literature and has the potential to offer a new way for the synthesis of these important structures in pharmaceuticals and radiopharmaceuticals.
- Brugarolas,Freifelder,Cheng,Dejesus
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- SYNTHESIS OF META-SUBSTITUTED [18F]-3-FLUORO-4-AMINOPYRIDINES BY DIRECT RADIOFLUORINATION OF PYRIDINE N-OXIDES
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Disclosed herein are methods for the fluorination aromatic N-heterocyclic N-oxides that comprise at least one leaving group. The N-oxides may be reduced to the fluorinated aromatic N-heterocyclic amine analogs. This novel fluorination approach may be successfully applied for synthesizing aromatic N-heterocyclic compounds labeled with 18F.
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Paragraph 0052
(2018/01/19)
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- Directed Lithiation of 4-Halopyridines: Chemoselectivity, Regioselectivity and Application to Synthesis
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4-Chloro and 4-fluoropyridines were ortho-lithiated by n-butyllithium-TMEDA chelate or lithium diisopropylamide at low temperature.The resulting 3-lithio 4-halopyridines were reacted with electrophiles which led to various 3,4-disubstituted pyridines.The versatility of this functionalization is enhanced by the 4-halogen reactivity towards nucleophiles such as water, methylate and amines.Some of the 3,4-disubstituted synthons were annelated to naphthyridine, xanthone and coumarin or condensed to Hantzsch-ester or to "chlotrimazol" analogues.Lithiation of 4-fluoropyridine led in one step to 3,4-pyridyne, which was trapped by cycloaddition with furans.
- Marsais, F.,Trecourt, F.,Breant, P.,Queguiner, G.
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