Acylhydrazines diacylhydrazines

Diazomethane is also produced in the reaction of acylhydrazines with dichloro-carbene, but the process is less efficient, as only one equivalent of diazomethane is produced from two equivalents of the acylhydrazine. However, the procedure provides a useful route to symmetrical AUV -diacylhydrazines (Scheme 7.25) [11],... 

The malonate derivative (93) reacted with acylhydrazine (94) to give a mixture of diacylhydrazine monoenamine (95) and oxadiazole (88c), (Scheme 6) which was also formed from (95) on heating <88LA909). 

Substituted acylhydrazones (95), formally derivatives of 1,2-diacylhydrazines (75), also cyclize to oxadiazoles (76), with loss of HX. Imidol ethers (95a R2 = H), prepared from acylhydrazines R1CONHNH2 and ortho esters HC(OR)3, cyclize on heating to monosub-stituted oxadiazoles (76 R1 = H). This reaction is an important synthesis of monosubstituted... 

Treatment of acylhydrazines with diazonium salts gives rise to tetrazenes (199) which can be readily dehydrated with base to give 1,5-disubstituted tetrazoles (Scheme 33). The reaction is also effective with 1,2-diacylhydrazines since one of the acyl groups is cleaved during the dehydrative cyclization, which may be conveniently carried out in situ without isolation of the tetrazene. This reaction can be useful for the synthesis of 1-aryltetrazoles using 1,2-diformylhydrazine as substrate (B-67MI41300). Mesoionic tetrazolium 5-oxides (8a) are obtained on treatment of bis(alkylsulfonyl)methanes with diazonium salts. Hydra-zones of type (200) are also obtained from these reactions and the tetrazenes... 

Oxadiazoles 165 result when W.W-diacylhydrazines are treated with the triphenylphosphiiie-carbon tetrachloride adduct in the presence of triethylamine <97PJC77>. Acylhydrazines 166 (R = Me, i-Pr, n-Bti, Ph or Bn) react with ketenylidenetriphenyl-phosphine 167 in boiling xylene to yield the 1,3,4-oxadiazoles 168 (Scheme 9) <97SL283>. 

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