1.23.4- Oxatriazole-5-oxides

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>. 

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. 

Several examples of the mesoionic 3-aryl-l,2,3,4-oxatriazole-5-oxide ring system 123 have been prepared by cyclisation of the arylhydrazones 122 these in turn are prepared from aryldiazonium salts and bromonitromethane <99KGS413>. 

This chapter covers the literature from mid-1995 to mid-2007. Recent advances include the preparation of the first A2-l,2,3,4-oxatriazolines 7 by intramolecular [3+2] cycloaddition (Section 6.08.9), synthesis of mesoionic derivatives 4 using bromonitroformaldehyde iV-arylhydrazones as the starting materials (Section 6.08.9), and detailed studies of the biologically active mesoionic oxatriazoles in the context of their nitric oxide donating capabilities (Section... 

No molecular ions appear in the electron ionization (El) spectra of mesoionic 1,2,3,4-oxatriazoles 4 and 6 or their derivatives. Instead, [M+ —30] peaks are observed due to loss of nitric oxide <1979J(P1)747, 1999CHE363>. The typical fragmentation pathway for such compounds and their analogues is summarized in Scheme 1 <1984CHEC(4)579, 1996CHEC-II(4)679>. In their fast atom bombardment (FAB) spectra, intact molecular ion peaks are observed for the A2-l,2,3,4-oxatriazolines 23 114 [M+H] and 24 142 [M+H] <2002HAC307>. 

Heterocycle (85) may be systematically described as 3-substituted anhydro-5-hydroxy-1,2,3,4-oxatriazolium hydroxide. However, this nomenclature is somewhat cumbersome and the terminology mesoionic has been used throughout this review. Thus compounds (85)-(87) and (91) are named mesoionic l,2,3,4-oxatriazol-5-ones (85), -5-thiones (86), -5-imines (87) and mesoionic l,2,3,4-thiatriazole-5-alkenes (91), respectively. Using IUPAC Rule. C-87 (85) is named 3-substituted l,2,3,4-oxatriazol-5-ylio oxide or 3-substituted l,2,3,4-oxathiazolylium-5-olate and (87 R = R1 = Ph) is named iV-[3-phenyl-5-(l,2,3,4-oxatriazolio)]anilide. 

The 1,2,3,5-oxatriazoles are known as oxatriazolines (112,113 X = O) and the thiatriazoles as thiatriazolines (114,113 X = S) and thiatriazolidines (115) often as 5-oxides. Recently the so-called non-classical heteropentalenes containing the 1,2,3,5-thia- and -selena-triazole ring system (116) have been prepared. 

N-Morpholino-W-nitrosoaminoacetonitril as a nitric oxide ( N0) donor (Bohn and SchOnafin-GER 1989, Feelisch et al. 1989) formed from N-ethoxycarbonyl-3-morphlinosydnonimine (molsi-domin) via 3-morphlinosydnonimine by 02 formation is a safe vasodilator in man, but a potential nasal carcinogen in the rat, probably due to the vast smooth endoplasmic reticulum with its cytochrome P450 (Hadley and Dahl 1982, Adams etal. 1991). The question whether the new series of mesoionic 3-aryl substituted oxatriazole-5-imine derivatives (Lahteenmaki et al. 1998) have the same side effects is outstanding. 

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