Formazan acylation

The alkylation of formazan anions (166) with methyl iodide yields the A-methylformazan (202) which cannot be prepared by direct methods (Scheme 31).4 However, formazans that contain hydroxyaryl (203) or heterocyclic groups (205) alkylate preferentially on these groups to yield the alkylation products 204349 and 206,346-348 respectively (Eqs. 24,25). Although formazans are resistant to acylation,334,350 351 it can be accom-... 

The use of 6-membered ring systems as sources of amidrazones to be converted into triazoles is relatively rare the case of 1-aminoadenine (Scheme 91) has already been mentioned. Transformations of 4,6-dihydrazinopyrimidine, hydrazines formed from haloaminopyridazine (81 HC(37)l, p. 8) and 1,2,4-triazines (8lHC(37)i, pp.409,424,488) all involve amidrazone intermediates cyclized to triazoles with the acyl function derived from the original ring. For instructive examples of preparative links between tetrahydrotetrazine, formazans and 1,2,4-triazoles, see Scheme 120 (81KGS694). 

A frequently used method for the preparation of 1,2,4-benzotriazines is the cyclization of formazans by treatment with sulfuric acid in acetic acid. When mixed formazans are used, both possible 1,2,4-benzotriazines 2 and 3 are formed.152 When acylformazans are used, 3-acyl-1,2,4-benzotriazines are isolated. The parent 1,2,4-benzotriazine is isolated when the formazan ester (R = C02R) is cyclized ester hydrolysis and decarboxylation also occur under these reaction conditions.153... 

Occasionally it is unnecessary to isolate the hydrazone since this is itself accessible by a coupling reaction. Numerous formazans can be obtained by treating compounds containing active methylene groups directly with 2 molar proportions of a diazonium salt. For example, pyruvic acid is converted into 3-oxalo-l,5-diphenylformazan (fi4formazylglyoxalic acid ) in 94% yield by benzenediazonium chloride in potassium hydroxide solution.351 Acyl groups (CH3CO or COOH) are often eliminated in such reactions 343,344,352 thus acetoacetic ester yields ethyl l,5-diphenylformazan-3-carboxylate almost... 

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