1.2.4- Triazolo quinazoline. mesoionic

Treatment of 3-amino-4-oxoquinazolines (9) with cyanamide gave the 2-amino-l,2,4-triazolo [l,5-c]quinazolines 11 as a result of cyclodehydration of the intermediate 3-guanidino-4-oxoquinazolines 10 (68CB2106) (Scheme 9). Similarly, reaction of the 3-amino-4-thioxoquinazoline 12 with alkyl or aryl isothiocyanates yielded the mesoionic l,2,4-triazolo[l,5-cjquinazolines 14 (84S881) (Scheme 10). 

Aminolysis of the 5-substituted-2-mercapto-l,3,4-thiadiazolo[3,2-c]-quinazolinium iodides 119 with butylamine afforded the mesoionic 1,3,4-triazolo[l,5-c]quinazolines 120 [77IJC(B)1110] (Scheme 44). 

Benzoxazinones (169, Z = O) or benzothiazinethiones (169, Z = S) underwent cyclization with thiosemicarbazide (83MI1), thiocarbohydrazide (86JHC43), or amidrazones (68CB2106 76MI1 85H2357) to give 1,2,4-triazolo[l,5-c]quinazolines (322). The mesoionic l,2,4-triazolo[l,5-... 

Syntheses of fused mesoionic heterocycles such as [l,2,3]triazolo[l,5-a]-quinoline, -quinazoline, -quinoxaline, and -benzotriazine derivatives have been described <02T3185>. Cyclizations of alkyl 2-benzoylamino-(4,5-dicyano-1 //-1,2,3-triazol-1 -yl)propenoates gave [1,2,3]triazolo[l, 5-a]pyrazines <02H(56)353>. Reaction of triethyl N-( 1 -ethy 1-2-methy 1-4-nitro-l//-imidazol-5-yl)phosphorimidate with aryl isocyanates provided a route to 2-aryI-2//,4//-imidazo[4,5-fif][l,2,3]triazoles <02JCS(P 1)1968>. 2-(A,A-Diphenylamino)-4-hydrazino-6-... 

The mesoionic l,2,4-triazolo[l,5-c]quinazolines 59 were obtained upon cyclization of the 4-thioxo-l,3-benzothiazines 57 with thiocarbohydra-zine through the intermediate 3-(4-thiosemicarbazido)pyrimidines 58 (86-JHC43) (Scheme 19). 

Much as in previous years, the majority of 1,2,4-T preparations have involved synthesis of ring fused species. Thus, final-step cyclization to the triazole has provided mesoionic triazolo [4,3-a]quinoxalines <97JHC1539>, 1,2-dihydro-l,2,4-triazolo[3,2-b]quinazolin-... 

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