Oxatriazoles

Attempts in this laboratory to prepare the analogous 1,2,3,4-selenatriazoles have so far been unsuccessful. Acyl azides show no tendency to cyclize to 1,2,3,4-oxatriazoles. ... 

Scheme 6.22 Acylation and nitrosation of 5-amenate derivatives of mesoionic 1,2,3,4-oxatriazoles.

Scheme 6.23 Ring-opening reactions of mesoionic 5-olate and 5-amenate 1,2,3,4-oxatriazoles to nitrosohydrazine derivatives.

Two types of nuclei with an oxygen and three nitrogen atoms are possible, namely 1,2,3,4-oxatriazoles (1) and 1,2,3,5-oxatriazoles (7). The neutral aromatic species have not yet been reported but 1,2,3,4-oxatriazolium salts (2) and mesoionic species (3)-(6) are known. 1,2,3,5-Oxatriazolium salts (8) and mesoionic compounds (9)-(12) are not yet known but 1,2,3,5-oxatriazolines (13) and (14) have been reported. The two types of oxatriazoles will be discussed in two separate sections. 

While the neutral 1,2,3,4-oxatriazoles (1) still await synthesis, some of their properties have been predicted by theoretical calculations. AMI calculations combined with a principal component analysis loading data from other related heteroaromatics have been used to estimate geometric characteristics, aromaticity, energy of formation, and N chemical shifts <90JPR885>. The oxatriazoles (1) and (7) and the 1,2,3,5-thiatriazoles, which also have not been prepared, are calculated to be in the group with the lowest classical and magnetic aromaticity. 

The mesoionic 1,2,3,4-oxatriazoles are crystalline, polar compounds which are usually recrystallized from methanol. Melting points are mid-range, frequently from 100°C to 150°C. 

Oxatriazol-5-ones Anhydro-5-hydroxy-l, 2,3,4-oxatriazolium Hydroxides) (271)... 

Analogous routes cannot be successfully employed for the synthesis of meso-ionic 3-aryl-l,2,3,4-oxatriazol-5-ones (271). Thus, nitrosation of 1-arylsemicarbazides yields arylazocarbonamides with loss of nitroxyl. Meso-ionic 3-aryl-1,2,3,4-oxatriazol-5-ones are formed by... 

Information concerning the chemistry of meso-ionic 3-alkyl- and 3-aryl-l,2,3,4-oxatriazol-5-ones (271) is limited, but further investigation may well be encouraged by reports of pronounced hypotensive activity. 3-Cyclohexyl-1,2,3,4-oxatriazol-5-one (271, R = cyclohexyl) is resistant to attack by dilute mineral acid, but warm concentrated sulfuric acid gives cyclohexanol and carbon dioxide. In contrast, acid hydrolysis of 3-phenyl-l,2,3,4-oxatriazol-5-one (271, R = Ph) yields phenyl azide. Meso-ionic 3-cyclohexyl-l,2,3,4-oxatriazol-5-one shows two unusual reactions its photoirradiation in benzene gives cyclohexanone and heating with diphenylacetylene )delds l-cyclohexyl-4,5-diphenyl-1,2,3-triazole (276) rather than the expected 2-cyclohexyl-4,5-diphenyl-1,2,3-triazole. 

In the early investigation of the nitrosation of 1,4-diphenyl-thiosemicarbazide (279, R = R = Ph), the product was obtained as deep red needles, m.p. 110°, and was allocated the remarkable 1,3-endoxyhydrazomethylene structure (280). Treatment of this deep red compound with warm aqueous alkali gave a colorless isomer, m.p. 157°, which was formulated as having one of the equally unacceptable structures 281 or 282. Recent investigations have established that nitrosation of 1,4-diarylthiosemicarbazides (279) yield the meso-ionic 1,2,3,4-oxatriazol-5-imines (277), which are transformed by base into the meso-ionic isomers (278). These alkaline transformation products formulated as meso-ionic l,2,3,4-tetrazol-5-ones (278) are in fact identical (see Section VII, J, 1) with substances prepared, but not formulated, by von Pechmann many years ago. ... 

Oxatriazole-5-thiones (Anhydro-5-mercapto-l,2,3,4-oxatri-azolium Hydroxides) (286)... 

The meso-ionic 1,2,3,4-oxatriazoles (286) yield phenol by acidic hydrolysis, phenyl azide by alkaline hydrolysis, and the 5-ethyl 1,2,3,4-oxatriazolium cation with triethyloxonium tetrafluoroborate. The rearrangement 286 -> 288 is achieved with boiling ethanolic ammonia. 

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