3-Halogenopyridine

Amination of the various four 2-halogenopyridines (24, X = F, Cl, Br, I) under analogous conditions gave 2-aminopyridine (25, Y = NH2) as the sole reaction product in greater than 85% yield.The mechanism of these reactions is discussed in Section II, A, 3. 

While awaiting the results of tracer experiments, the present authors prefer to desist from assuming that the route from 24 to 25 via the addition product shown is the only pathway followed in the amination of 2-halogenopyridines. This is the more so since it seems probable that in the experiments described below derivatives of 2,3-pyridyne occur as intermediates. 

Azaallyl anions, generated by treatment of arylmethylidene(arylmethylamines) with lithium diisopropylamide (LDA), react with 2-halogenopyridines to give a variety of substituted [l,7]naphthyridines (Scheme 47) <1995J(P1)2643>. 

The other major approach to triazolo[4,3-a]pyridines is from pyridines or from 2-halogenopyridines, with the addition of a three-atom fragment to form the triazole ring. Reaction between pyridine or 4-methylpyridine and... 

A significant decrease of the efficiency was observed when the resin was recycled, together with a coloration of the resin, possibly due to contamination with the palladium catalyst (Pd(PPhj)4). This observation was subsequently verified in the cross-coupling of supported aryltins with 2-halogenopyridines by washing the resin with trithiocyanuric acid, which led to a recovery of the cross-coupling efficiency at least on the first reuse. ... 

Potassium/tert-butylalcohol 2-Pyridones from 2-halogenopyridines... 

Ethyldiisopropylamine s. under BFf Tri-n-butylamine s. under 2 Halogenopyridine methiodide Calcium sulfate s. under Cation exchanger... 

Halogenopyridine methiodideJtri-n-butylamine o-Halogenocyclimmonium salts as condensing agents Carboxylic acid esters from carboxylic acids and alcohols... 

Halogenopyridine methiodideftri-n-butylamine Carboxylic acid amides from carboxylic acids s. 32,148... 

For pyridine, the picolines and the 3-halogenopyridines, the intensity of absorption in the region 34-37,500 cm i decreases when the solvent is changed from iso-octane to ethanol, and that at about 38,500 cm i increases. In the 2-halogenopyridines, the n->rr transition cannot be clearly identified because it is shifted to shorter wavelengths and obscured by the 77 77 band. According to Sklar s vectorial treatment, the intensities of... 

Nuclear quadrupole resonance studies of chloro- and bromopyridines have been used to examine the charge distribution in the heterocyclic ring. The charge density at a nuclear carbon atom can be related to Hammett substituent constants, and the quadrupole resonance frequencies of halogen atoms at C(3) and C(5) in pyridines can be related satisfactorily to the Hammett constant for the heterocyclic nitrogen atom. However, the relationship breaks down for 2-halogenopyridines, and the quadrupole resonance frequencies indicate , in these cases, an increase in the carbon-halogen bond order (35). 

The halogenopyridines are susceptible to nucleophilic substitution (p. 210), and quaternary salts from pyridine and 2-chloro-, -bromo- and -iodo-pyridine have been described 24, 2-Halogenopyridines and -quinolines react... 

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