1- Substituted 1,2-diacylhydrazines, cyclization

Reaction of 232 with 4-substituted l,3-oxazol-5(4/7)-one 247 led to diacylhydrazines 248 or to imidazole derivatives 249 depending on the reaction temperature (Scheme 24). l,2,4-Triazole-3-thione 250 was obtained by a two-step sequence from 232 with phenyl isothiocyanate and subsequent base-catalyzed cyclization of thiosemicarbazide 251. The effects of hydrazones 241-246 on inhibition of photosynthetic electron transport in spinach chloroplasts and chlorophyll content in the antialgal suspensions of Chlorella vulgaris were investigated <2005CEC622>. 

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... 

Tandem sequences have also yielded some interesting pyrazole structures. Four-component coupling of terminal alkynes 37, hydrazines 38, carbon monoxide and aryl iodides furnished pyrazoles 39 in the presence of palladium catalyst <05OL4487>. Fully substituted 1/f-pyrazoles 42 were prepared from the condensation/fragmentation/cyclization/extrusion reactions of thietanone 40 with 1,2,4,5-tetrazines 41 <05JOC8468>. Reactions of isocyanides 43 and dialkyl acetylenedicarboxylates 44 in the presence of 1,2-diacylhydrazines 45 led to highly-functionalized pyrazolines 46 <05TL6545>. 

Diacylhydrazines 1 or dichloro-substituted azines 3 are cyclized with hydrazine to give the dihydro-1,2,4,5-tetrazines 4 which are converted to 1,2,4,5-tetrazines 5 by oxidation with the usual oxidation agents.4 5 27,165 - 168 The use of the dichloro azines 3 (see Houben-Weyl, Vol. 10/2, p 164) appears to be the better method. Since 3 can be prepared either from 1 or... 

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