1.2.4- Triazolo oxadiazoles

Rearrangement of oxadiazole bearing quinoline 772 gave the triazolo-quinolinyl ketoxime 773 (93H1577) (Seheme 135). 

An unusual intramolecular cyclization reaction was demonstrated for 4,4 -diamino-3,3 -azofurazan 166. The 5-(4-amino[l,2,5]oxadiazolyl)-5/7-[l,2,3]triazolo[4,5-f][l,2,5]oxadiazole 167 was formed by boiling compound 166 with Pb(OAc)4 in PhCl or o-Gl2CgH4, or by boiling it in SOCl2 (Equation 29) <1996KGS253>. 

The cyclocondensation of 3-acyl/3-aroyl-5-aryl[l,3,4]oxadiazol-2(3//)-ones 98 with hydrazine hydrate gives the corresponding 3,6-disubstituted-[l,2,4]triazolo[3,4- ][l,3,4]oxadiazoles 99 (Equation 26) <1991H(32)237>. 

The reaction of 5-aryl-3-(chloromethyl)[l,3,4]oxadiazole-2(3//)-thiones 100 with hydrazine or methylhydrazine yields the corresponding 2,3-dihydro[l,2,4]triazolo[3,4-A][l,3,4]oxadiazole derivatives 102 <1984JCED477>. By analogy, hydrazine and phenylhydrazine convert the [l,2,4]triazole-2(3//)-thiones 101 into 3,7-dihydro-2//-[l,2,4 tria-zolo[4,3-r][ 1,2,4] triazoles 103 <1992PS99, 2002JCCS1035>. Finally, the azole-2(3//)-thiones 101 react with hydroxylamine to form the 3,7-dihydro[l,2,4]triazolo[5,l-d[l,2,4]oxadiazoles 104 (Scheme 8) <1992PS99>. 

Some rearrangements in the 1,3,4-oxadiazole series are explained by an /pso-nucleophilic attack by the side-chain (Scheme 72). Thus, under amination conditions, oxadiazolyl ketones 458 give the rearranged thia-zoles 460 via the enamino compounds 459 as intermediates. Sometimes, performing the reaction in refluxing acetic acid causes direct cyclodehydration into thiazolo[2,3-c]-s-triazoles. In a similar way, hydrazine in refluxing acetic acid converts compounds 458 into triazolo(3,4-b)thiadiazines 463... 

Reaction of the potassium salt of the [l,2,3]triazolo[4,5-d [l,2,5]oxadiazole 2-oxide 68 with AgNOs furnished the corresponding silver salt whilst the parent bicycle was obtained on acidification < 1996TL8577 >. Methylation of either the silver salt, or the parent bicycle, led to mixtures of the IV- and 0-methylated derivatives 67 and 69. In each case the selectivity of the reaction differed, the parent showed a 9 1 preference for the A-substituted derivative however, the 0-methylated product dominated and 67 and 69 resulted in a 4 3 ratio in the reaction starting from the silver salt (Scheme 5) <1996TL8577>. 

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