2-Azidopyridine 1-oxides

Irradiation of the 2-azidopyridine 1-oxides (142) in benzene affords the 6-cyano-1,2-oxazines (143).A pathway involving photoelimination of nitrogen and ring... 

Azidopyridine 1-oxides undergo ring contraction on thermolysis to give the much sought after 2-cyano-A -hydroxypyrroles (93). This reaction, however, is not thought to involve a nitrene. 

H- 1,2-Oxazines are stabilized as 4,4-disubstituted derivatives but 4H- and 6if-l,2-thiazines are almost unknown. Possibly the paucity of these compounds simply reflects a lack of interest, for 6if-l,2-oxazines are comparatively common, and 3,5-diphenyl-6if- 1,2-oxazine, for example, is a stable crystalline solid. Similarly, cyano-1,2-oxazines (6 R=alkyl) are formed by the photolysis of azidopyridine oxides (5). However in the case where R3 = H, these products rearrange to pyrroles (7) (81CC36). 

The thermolysis of 2-azidopyridine iV-oxides leads to Ar-hydroxy-2-cyanopyrroles (185 — 186) (73JOC173) (see also Section 3.4.3.11). 

Azidopyridines (165) exist as the tetrazoles 166, but with DMAD they give the adducts 167.321 4-Azidopyridine 1-oxide (168) adds DMAD to give 169, but in methanol the reaction takes a different course giving 171, possibly by way of 170.321... 

Photolysis of 4-azidopyridine-l-oxide in acetone under nitrogen gave a 37% yield of 4,4 -azopyridine-l,r-dioxide. When the photolysis was carried out in the presence of oxygen 4,4 -azoxypyri-dine-ljT-dioxide was obtained in 27% yield. 

The ring contractions of 2-azidopyridine N-oxides (328) to 1-hydroxy-pyrroles,371 and of 2-azidoquinoxaline 1,4-dioxides (329)372 (Scheme 67) are also believed to be assisted nonnitrene reactions, as symbolized in formula 328, because they generally take place in solution below 100°C. 

Thermolysis of 3-substituted 2-azidopyridine JV-oxides at 90°C was originally thought to give 2/Z-pyrrole iV-oxides (121a, 80-90%, Scheme 44).117 However, the product was recently to shown to be the isomeric oxazine 121b.117a... 

Heating 2- and 4-dialkylamino-3-azidopyridines 104 in nitrobenzene at 170°C results in a loss of nitrogen from the azide group to give a nitrene that attacks the K-methylene group of the o-dialkylamino substituent with further formation of dihydroimidazoles 105, which are then oxidized by nitrobenzene to IPs 106. Here IcP yields are 40-70%, and the yields of IbPs do not exceed 1(U15% (63JCS1666). 

A number of pyridyl azides have been prepared by conventional methods. The reaction of 4-hydrazino-2-picoline with nitrous add, for example, gives 4-azido-2-picoline. 4-Azidopyridine-l-oxide is obtained in a similar manner. The reaction of 4-chloropyridine with sodium azide is less satisfactory, and gives the product in low yield. ... 

Pytidylazide is formed by reaction of 3-pyridyldiazonium chloride with sodium azide. 2-Aminopyridine-l-oxides can be diazotized, and treatment of the salt with azide ion gives rise to the 2-azidopyridine-l-oxide in good yields. ... 

Huisgen and his co-workers have investigated the reaction of 2-pyridylazide with various acetylenes. Although the equilibrium is largely toward the tetrazole, the substance reacts to give l-(2-pyridyl)-l,2,3-triazoles (Vni-7). (See Ch. IA for some reactions of 2-azidopyridine-l-oxides.)... 

The identification and determination of 2,4-, 2,5-, and 2,6-dinitrophenols by their color reactions with 2-aminopyridine have been reported. 2-Aminopyiidine-l-oxide gives a blue color when it is heated with 7V,7V-dimethylaniline and concentrated hydrochloric acid. On diazotization and treatment with azide ion it yields 2-azidopyridine-l-oxide. ... 

Other intramolecular conversions show the formation of tetrazolo[l,5-a]pyridines through the conversion of pyridine A -oxides into the corresponding 2-azidopyridines. These azides exist in equilibrium with the tetrazoles, resulting from the cycloaddition of the azide with the pyridine ring. The ratio of the equilibrium is dependent on the substitution of the heterocycle however the tetrazole usually dominates the azide species and can be converted into several other derivatives via hydrogenation, alkylation or arylation. ... 

Photolysis of N-oxides of 4-azidopyridine and 4-azidoquinoline gave corresponding azocompoimds [22], or hydrogen-abstraction products [23], No ring-expansion products were detected [23], It is interesting, that no cross-over azocompound was obtained during photolysis of the mixture of two N-oxides of the azides [22],... 

Upon laser flash photolysis of 4-azidopyridine-1-oxide at room temperature in 3-methylpentane at 266 or 308 nm two temporally distinct featmes were... 

R.A. Abramovitch, B. Bachowska, P. Tomasik, Thermal and photochemical decomposition of 3- and 4-azidopyridine 1-oxides in nucleophilic solvents,... 

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