Arylhydrazones, halogenation

In the presence of sodium acetate in acetic acid, the arylhydrazones 54 (available from the reaction of tu-halogen-tu-(arylhydrazono)acetophenones with 3-amino[l,2,4]triazole) undergo cyclization to yield 3-aroyl-l-aryl-l//-[l,2,4]-tria-zolo[3,4-c][l,2,4]triazoles 55 (Equation 7) <1987CB965>. 

Nitrobenzaldehyde arylhydrazones with a halogen give compounds (453), which on treatment with base form 2-aryl-4-oxido-l,2,3-benzotriazinium betaine 1-oxides (454 R = Ar) (74JOC2710). 

C7H6N3O2R2R7 i mw I64.I6+R2+R7 yel crystn compds sol in coned hydrochloric acid and hot ethanol. The compds are stable at RT for indefinite lengths of time (Ref 12, pp 88-90). Table 1 presents specific properties of these compds. Prepn, in general, is by halogenation of 2-nitrobenzaldehyde arylhydrazones (with an R7 fragment already attached), followed by treatment with a base contg the R2 fragment... 

Furthermore, direct halogenation sometimes leads to substitution in the C-residue of the aldehyde hydrazone. For example, hydrazonoyl bromide 28c was obtained by direct bromination of hydrazone 58a or 58b (75CJC1484). Electron-withdrawing substituents in the N-aryl moiety of the arylhydrazone derivatives of heterocyclic aldehydes inhibit ring bromi-... 

The halogenation of the arylhydrazones of arylaldehydes is an excellent method of synthesis of hydrazidoyl halides. However, halogenation of the ring attached to nitrogen can not be avoided. For example, reaction of benzaldehyde phenylhydrazone (XI) with bromine in glacial acetic acid... 

The halogenation of arylhydrazones of arylaldehyde has been extended to the arylhydrazones of ethyl acetoacetate (5-s.10,13,17,30,31,95 yot example, reaction of XIX with bromine in glacial acetic acid/acetic anhydride, in the presence of sodium acetate, affords the hydrazidoyl bromide XX in excellent yield ( ). 

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