Oxadiazolium halides

Just as in the case of the 1,3,4-oxadiazolium halides, ring cleavage of the l,3,4-oxadiazolin-5-ones and -5-thiones can be achieved. These reactions using ammonia,146 amines,146 and hydrazine146 have been... 

Ring transformation of 2-amino-3-phenacyl-l,3,4-oxadiazolium halides with amines, liquid ammonia, or heterocyclic bases yields 2-amino-l-acylamino-4-arylimidazoles.145... 

Ring transformation of 2-amino-3-phenacyl-l,3,4-oxadiazolium halides with amines, liquid ammonia or heterocyclic bases gives l-acylamino-2-amino-4-arylimidazoles [57], When treated with an a-halogenoketone in ethanol 2,5-diamino-1,3,4-thiadiazolcs form salts, which react with hydrazine hydrate to give l-aminoimidazolin-2-thiones [58],... 

Amino-1,2,4-triazoles (50) or their derivatives are usually starting material for the synthesis. They are readily available and already contain the exocyclic N-N bond required for heteroaromatic A-imines. 4-Amino-1,2,4-triazoles can be quaternized by alkyl halides or tosylates at the N-l atom to give the salt 52.79-82 (Scheme 5) The orientation of quatemization is proved by the reactions in Scheme 6 for the example of the quaternary acylamino salts 52. Quaternary salts of the type 52 can also be prepared by reaction of 1,3,4-oxadiazolium salts (51)83 with aryl hydrazines84 and from aryl hydrazine hydrohalides and orthoesters.86 With alkali, the 1-alkyl-s-triazole-4-imines8(7-82 86 can be obtained in the normal manner from these salts (Scheme 5). The free A-imines are all stable except the A-unsubstituted compound itself.87 Recently, other structures were tentatively reported 88 for the deprotonation products of analogous quaternary salts (52) with hydrazine. 

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