1.2.3- Triazolo pyrimidinones

Diacetylcyclopropane reacts with 3-amino-l, 2,4-triazole in acetic acid (either aqueous or glacial) to give triazolopyrimidines 28 <%1ZV1322>, whilst a selection of fiised-ring pyrimidines, for example the l,2,3-triazolo[4,S-prepared using amino hetmoarenecarboxamides and esters <96H(42)691 >. 

The 4-hydrazino-pyrazolo[3,4-rf]pyrimidine derivative 80 yields pyrazolo[4,3-e]-[l,2,4]triazolo[4,3-c]pyrimidinones 82 through hydrazone derivatives 81 <00JCS(P1)33>, these compounds being a new class of potential xanthine oxidase inhibitors. 

Amino-2-hydrazino-4(3//)-pyrimidinone (397) and orthoesters in hot acetic acid or BuOH gave l,2,4-triazolo[4,3-a]pyrimidin-7(8//)-ones 398. When the heating in acetic acid was continued overnight, the acetamido derivative 399 was obtained. In acetic acid at room temperature, the re-... 

The triazolo[l,5-c]pyrimidinone 501 was prepared by converting uracil and its 6-methyl derivative 498 into the corresponding 4-thio derivatives (499) and thence into the hydrazinopyrimidinone 500. This underwent cy-clization in boiling formic acid, triethyl orthoacetate, or triethyl orthobenzoate to the triazolo[l,5-c]pyrimidinones 501 (80AJC1147) (Scheme 98). 

Azahypoxanthines of type 116 were obtained via an annulation reaction by heating 5-acylamino-4-carboxamido-l, 2,3-triazole with excess hexamethyldisilazane (HMDS) in xylene (95FA257). 3-Aryl-l,2,3-triazolo [4,5-[Pg.104]

Nucleosides in the j-triazolo[2,3- ]-5-pyrimidinone and 5-triazolo[4,3-a]-7-pyrimidinone series have been synthesized by way of silyl or fusion procedures. The former procedure afforded the kinetically favoured product (354) substituted in the triazole ring, whereas the fusion procedure yielded the thermodynamically favoured product (355) substituted in the pyrimidine ring. 

---