Oxatriazole

CN3O 0 N N N Mesoionic 3-phenyl-l,2,3,4-oxatriazole-5-phenylimine mesoionic 3-phenyl-l,2,3,4-oxatriazol-5-one... 

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. ... 

A comparison of MP2/6-31G structural parameters of 1,2-oxazole 19 (isox-azole) and 1,3-oxazole 20 with microwave data is provided by Kassimi et al. (Scheme 16) [96JPC8752]. The general agreement is excellent. The same authors investigated dipole moments, quadrupole moments, octopole moments, and dipole polarizabilities of 19 and 20 together with several oxadiazoles and oxatriazoles [96JPC8752, 99JPC(A) 10009]. For the mean polarizability of these species, they found the approximative formula... 

Formation of the bicyclic lithiated intermediate 8 is considered to be a two-step process whereby the nitrogen atom of nitric oxide attaches to the Cl atom of propynyllithium. Addition of a second molecule of nitric oxide gives intermediate 8 that on reaction with water produces 5-methyl-l,2,3-oxatriazole 3-oxide 9 (Scheme 1). Calculated, optimized geometry and bond lengths for stmcture 9 together with calculated infrared (IR) and Raman spectra are reported <2005JOC5045>. 

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.

Tandem nucleophilic substitution-[2+3] cycloaddition reaction of 4-bromo- and 4-toluenesulfonyloxy aldehydes 77 with sodium azide in DMF at 50 °C affords excellent yields (>80%) of substituted pyrrolo[.2.3.4]oxatriazoles 78 (Scheme 8) <2002HAC307>. 

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. 

The synthesis of mesoionic oxatriazoles was reported as early as 1896 <1896CB2161>, but the structure was first proved in 1964 <64JCS906>. The original method of preparation is still in use, but alternative procedures have been developed. Activity in the field peaked in 1979 and in the period... 

The mesoionic compounds can be named in several ways. The systematic name for structure (4) is a 3-substituted anhydro-5-hydroxy-l,2,3,4-oxatriazolium hydroxide. Similarly, structure (5) is named a 3-substituted anhydro-5-thiolo-l,2,3,4-oxatriazolium hydroxide, and structure (6) a 3-substituted anhydro-5-amino-l,2,3,4-oxatriazolium hydroxide. Frequently used names for structure (4) are 3-substituted 5-hydroxy-1,2,3,4-oxatriazolium hydroxide inner salt Chemical Abstracts), 3-substituted l,2,3,4-oxatriazol-5-ylio oxide, or 3-substituted l,2,3,4-oxathiazolylium-5-olate. For practical purposes, the term mesoionic l,2,3,4-oxatriazol-5-one is often used. Analogously, (5) and (6) are named mesoionic l,2,3,4-oxatriazol-5-thione and mesoionic l,2,3,4-oxatriazol-5-imine, respectively. 

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. 

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