Dioxo-l,2,4-triazolidine

Partially or fully reduced triazoles are relatively unstable and have not aroused great interest except for those with exocyclic double bonds, which retain the potential aromatic character of the parent triazole. Compounds such as triazolinone (2) and 3,5-dioxo-l,2,4-triazolidine (urazole) (3) will be treated as triazoles, since they can be written in the tautomeric triazole forms (2a) and (3a) (Equations (2) and (3)). 

A few trivial names for 1,2,4-triazoles are in common use 3,5-dioxo-l,2,4-triazolidines (5) are called urazoles, and the corresponding 3,5-diamino compounds (6) guanazoles. 

In contrast to thermal uncatalyzed reactions of /V-acylsulfinylamines with aryl isocyanates which give rise to azoarenes,188 the cobalt or iron carbonyl-catalyzed process gives additionally 3,5-dioxo-l,2,4-triphenyl-1,2,4-triazolidine (Scheme 124).189 The only possible restriction on this simple urazole synthesis would be the expectation that the substituents on the reactants must be the same to prohibit exchange. 

Aminourazole 4-Amino-3,5 -dioxo- ym-triazolidine 4-Amino-3,5-dioxo-l 2,4-tri-ozolidine (called p-Vrazine in JCS 95, 237) [Called in Beil, 4-Amino-3.5-dioxo-1.2.4-triazolin], OC-NH-NH. Crysts, mp 273... 

A special case of these ring transformation reactions is the 5-insertion reaction of 4-phenyl-1,2,4-triazolin-3,5-diones (4 Ph-TAD) [750PP251 81AG832, 81AG(E)797] into uracils, for example, the reaction of 5-(3,5-dioxo-4-phenyl-l,2,4-triazolidin-l-yl)-l,3-dimethyluracils with hydrazine... 

Hydroxytriazoles and tautomeric triazolinones have a common mesomeric anion, hence their spectra are affected in basic solvents. UV spectra have been used to demonstrate the predominantly dioxo structure of l-phenyl-l,2,4-triazolidine-3,5-dione (66T(S7)213) and the thione structure of mercaptotriazoles (66ACS57) utilized also in theoretical work. 

Dioxo-4,8-diphenyl-l,3,5,7-tetraaza-bicyclof3.3.0]octan laBt sich durch Lithium-alanat in5-Hydroxy-3- phenyl-1,2,4- triazolidin (14% d.Th.), N-Methyl- benzylamin auf-spalten4 ... 

Triazolidin 3,5-Dioxo-l-methyl-4-phenyl- E4, 1138 (aus dem Onium-Salz)... 

Figure 4 Structure of the l-(diphenylaminoaminylio)-3,5-dioxo-A-phenyl-, 2,A-triazolidin-l-ide molecule...

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