2-Methylpyridine V-oxide

Certain heteroaromatic compounds that have acidic methyl groups are effective in the Knoevenagel condensation. 6-Methyl-1,3,5-triazine (156), 2-methylpyridine V-oxides (157), quinolines and pyrimidines all condense with aromatic aldehydes in the presence of the usual catalysts. An example of a doubly activated methylene compound in which one activation group is a heterocycle is the 2-oxopro-pylthiazole (158), which condenses with a number of aldehydes. " ... 

Methylpyridine V-oxides react with hot acetic anhydride and produce 2-acetoxymethylpyridines using trifluoroacetic anhydride permits reaction at room temperature with fewer by-products. " Repetition of the sequence affords 2-aldehydes after hydrolysis. " The course " of the rearrangement would seem to be most simply explained by invoking an electrocyclic sequence, as shown below. 

For Negishi reactions in which the pyridines are nucleophiles, the pyridylzinc reagents are usually prepared from the corresponding halopyridines [6, 20, 21]. An excess of 2-chlorozincpyridine /V-oxide (26), arising from 2-bromopyridine N-oxide hydrochloride (25), was coupled with vinyl triflate 27 in the presence of Pd(Ph3p)4 to furnish adduct 28 [20]. Recently, an efficient Pd-catalyzed cyanation of 2-amino-5-bromo-6-methylpyridine (29) using zinc cyanide has been reported to afford pyridyl nitrile 30 [22]. 

C1 4H2 4MO3N4O13, Tetramethylammonium (/Li3 methoxy )-tris(/x methoxy )-tris(dicarbonyl-nitroso-molybdenum), 46B, 1165 Cl4H26O12S2Zn, Zinc hexa-aquo p-toluenesulphonate, 21, 585 C1 aH27Fi,N203Ta, Tetraethylammonium tetrafluoro(2-methylpyridine N-oxide)peroxotantalate(V), 43B, 1364 Cl5H28CI6CU4N3O5 C5H9NO, Mfl Oxa-hexa-/x"chloro-(aquo-copper(II))-tris(N-methyl-2-pyrrolidinone-copper(II)) N-methyl-2-pyrrolidinone solvate, 45B, 1216... 

Methylpyridine methiodide condenses with Ar,Ar-dimethyl-4-nitrosoaniline in the presence of piperidine to give the Schiff base (66 Scheme 53). The reaction fails with 2-methylpyridine itself but (V-oxide analogues condense similarly (63JCS4600). 9-Methyl-acridine condenses with C-nitroso compounds to yield anils or nitrones. 

Abbreviations 4-pic, 4-methylpyridine PNO, pyridine /V-oxide pip, piperidine PhjAsO, triphenylarsine oxide DPM, 2,2,6,6-tetramethylheptane-3,5-dione. 

In the study of the oxidation of 2-methylpyridine on this type of catalyst Nadezhdina et al.130 observed a comparable activity and selectivity for a- and /3-vanadyl polyphosphates as found for the traditional V-Mo-oxide catalysts. 

Skolmeistere et al.136 studied the oxidation of 2-methylpyridine and pyridine-2-carboxaldehyde on a V-Mo oxide catalyst and observe that the main products formed in the second case are high-molecular condensation products and that a small amount of 2-picolinic acid is formed directly from the first compound. 

Phenyl, 4-methoxyphenyl, and 4-ethoxyphenyl tellurium thiocyanates are known only in the form of their complexes with thiourea1,2 ethylenethiourea3, triphenylarsine oxide, 3-methylpyridine, 3-methylpyridine /V-oxidc, or 4-methylpyridine Af-oxide2. These compounds were prepared from the diaryl ditellurium compounds, thiocyanogen, and the ligands2. 

Nitrogen also can be a site of attack for oxygen atom transfer from a fluoroox-aziridine. 2-Methylpyridine (316) was converted to its V-oxide (317) in 70% yield by oxaziridine 301 under very gentle conditions. 

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