2- azidopyridines

A closely related reaction is the formation of 5T/-1,3-diazepines 7 when 2-azidopyridines 6B are irradiated in the presence of a base, such as sodium methoxide or diethylamine. The reaction only succeeds in the presence of electron-donating substituents (R = OMe. OPh or NEt2) other 2-azidopyridines exist predominantly in the tetrazolopyridine form 6 A and are photostable.161... 

Novel calculations on the tetrazolo[l,5-tf]pyridine-2-azidopyridine equilibrium (Scheme 2, 1-7) in the case of 5-substituted derivatives using ab initio (6-31G /MP2) methods appeared recently <2000T8775>. It has been shown that these substituents sensitively influence the equilibrium as revealed by the calculated energies shown in Table 1. 

Novak et al. <1998JA1643> devised a novel approach to amino-substituted tctrazolo[ 1,5-tf Jpyridine which provides a really unique pathway (Scheme 34). These authors studied the possibility of formation of nitrenium ions from the pivaloylhydroxylamine 143 and found that if azide anion is present in the main reaction route is the formation of tetrazolo[l,5-tf]pyridine 146. The authors concluded that the first intermediate is the formation of the carbonium cation 144 which captures the azide anion to yield 2-azidopyridine 145, that is, the valence bond isomer of the product 146. 

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... 

Obviously the investigator should also be aware of any ground state reactions peculiar to the system under study. For example 2-azidopyridines isomerize to tetrazoles which are usually less sensitive than the azide to irradiation (Fig. 3.1). The position of the equilibrium is both temperature, solvent and pH dependent. Even if the equilibrium constant for such an isomerization in solution is known the situation in a ligand binding site cannot be predicted. Azide-tetrazole isomerization was an important consideration in experiments using 2-azidoadenine derivatives which have recently been described by MacFarlane et al. (1982). 

Azide derivatives of azines also equilibrate to give polyaza bicyclic heterocycles <2010T2863>. In the tetrazolo[l,5- ]pyridine-2-azidopyridine equilibrium 311 312, substituents on the pyridine ring influence the position of the equilibrium <1997MRC237>. For another example, see Scheme 16 in Section 2.2.5.3. 

Thermolysis of 2-azidopyridine 25 at 480 °C generates the nitrene, which rearranges at low temperature to the cyclic carbodiimide 26. At -70 °C the carbodiimide band in the infrared spectrum disappears and the isolated product is 2-cyanopyrrol 27 ... 

The decomposition of 2-azido-4,6-dimethylpyrimidine (186) (in equilibrium with the tetrazolo compound 185) in the presence of copper acetylacetonate in cyclohexane at 140° gave the hydrogen abstraction product (187) (46%) and C—H insertion product (188) (8-5%) The same products were obtained in essentially the same yields by thermolysis of 186 at 185° °, (see section III.B.5). It was felt that the reaction proceeded via a copper-nitrene complex. The copper-catalysed decomposition of 186 and also 2-azidopyridine (in... 

Variously substituted tetrazolo[l,5-a]pyridines (19) and 2-azidopyridines (20) are photolysed to 2-alkoxy-lH-l,3-diazepines (21), 2-dialkylaraino-5H-1,3-diazepines (22), 2,3-dihydro-lH-l,3-diazepin-2-ones (23), and 2,4-diazabi-cyclo[3.2.0]-hepten-3-ones (24) the relative stabilities of the 2-alkoxy- and... 

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. 

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... 

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