1.2.3- Triazolo pyrimidine-5,7-diones

Heating the 5-isocyano-l,3,4-thiadiazolo[3,2- ]pyrimidin-5-one 115 with 10% hydrochloric acid gave a mixture of the 5-imino-l,3,4-thiadiazolo[3,2- ]pyrimidin-7-one 116 (10%) and the l,2,4-triazolo[l,5-c]pyrimidine-5,7-dione 117 (35%) (91JHC489). Formation of 117 probably occurred through thiadiazole ring rupture of 116 and recyclizatioii with its imino function together with desulfurization (Scheme 43). 

Ultraviolet (UV) spectroscopy does not tend to be the method of choice for structure determination, but a list of UV absorptions was given in the review by Knowles <1996CHEC-II(7)489>. Fluorescence properties and triplet yields of [l,2,3]triazolo[4,5-r/ pyridazines in various solvents have been reported <2002JPH83>. These heterocyclic systems were found to be photochemically very stable. In a recent paper, Wierzchowski et al. studied the fluorescence emission properties of 8-azaxanthine ([l,2,3]triazolo[4,5-r/ pyrimidine-5,7-dione) and its A -alkyl derivatives at various pH s <2006JPH276>. For the 8-azaxanthines, an important characteristic of emission spectra in aqueous solutions was the unusually large Stokes shift. Since 8-azaxanthine is a substrate for purine nucleoside phosphorylase II from Escherichia coli, the reaction is now monitored fluorimetrically. The fluorescence properties of [l,2,3]triazolo[4,5-r/ -pyrimidine ribonucleosides were earlier described by Seela et al. <2005HCA751>. 

Methyl-5-oxo-l,5-dihydro-8-carbamoyl-l,2,4-triazolo[4,3-c]pyrimidines 577 and 578 were prepared by the cyclization of 576 with acetic anhydride and ethyl oxalate, respectively (89PHA604).The 4-methyl-l,2-dihydropyra-zolo[3,4-d]pyrimidine-3,6-dione 579 also was obtained in the latter case, as a consequence of breaking the amide bond and releasing the amine moiety. Coupling ethyl dithioacetate and 5-chloro-4-hydrazinopyrimidine (580) afforded the triazolo[4,3-c]pyrimidine 581 (89H239) (Scheme 114). 

Hydrolysis of 2-phenyl-[l. 2.3]triazolo[4,5-d]pyrimidine-5,7-dione N-oxides 463 in basic solution gives rise to 4-amino- and 4-ureido-2-phenyl-l,2,3-triazole-5-carboxylic acid 1-oxides 464, as well as their hydrazides and methylamide (2005JGU636) (Scheme 134). 

Other claims are the isothiazolo[4,5-d][l,2,3]triazine-4-ones (170) for the treatment of gout and eschemia <86EUP274654>, the 3-aryl[l,2,5]thiadiazolo[3,4-d]pyrimidine-7-ones as antiallergics <90EUP349239>, 3-dialkylaminoethyl-l,2,3-triazolo[4,5-d]pyrimidine-5,7-diones as bronchodilators <88EUP272226>, and the 5-aryl-1,2,3-triazolo[4,5-d]pyrimidines as antihypertensives <88USP4923874>. 

Dealkylation, of azolium quaternary salts and betaines, 60, 244 Deazaflavines, bent, 55, 192 5-Deazalumazines, see Pyrido[2,3-(/]pyrimidine-2,4-diones Deaza-purines, -flavines, etc., see the systematically-named ring systems 4-Deazatoxoflavins, syntheses, 55, 182 Dechlorination, catalytic, of chloro-[ 1,2.4]triazolo[ 1,5-a]pyrimidines, 57, 125... 

An interesting approach for the synthesis of some fused pyrimidines has been reported by Shaaban [102] via reaction of 4,4,4-trifluoro-l-(thien-2-yl)butane-1,3-dione in the presence of triethylorthoformate with 5-aminopyrazole or 1,2,4-aminotriazole or 2-aminobenzimidazole under microwave irradiation. The resulting trifluoromethyl derivatives of pyrazolo[l,5-a]pyrimidine 56, l,2,4-triazolo[l,5-a] pyrimidine 57 and pyrimido[l,2-a]benzimidazoles 58 were obtained in excellent yields and purity (Scheme 42). 

A derivative of a hitherto unknown nucleus was produced when 4-amino-5-aminomethyl-3-methyltriazole was refluxed with carbon disulfide and triethylamine in pyridine, which yielded 3-methyl-3,7-dihydro-l,2,3-triazolo-[4,5-d][l,3]thiazine-5-thione (98) (3 hr, 53%) the 3-benzyl analog was made similarly (63%) [80JCS(P1)2009]. Cyclization of 4-anilino-5-ethoxycarbonyltriazole with polyphosphoric acid produced 1 f/-triazolo-[4,5-h]quinol-4-one (99) [80EUP(A)2562]. Similarly, ring closure of 4-(2-pyridylamino)triazole-5-carboxylic acid (or its esters) gave l//-pyrido-[l,2-a]-l,2,3-triazolo[4,5-d]pyrimidin-4-one (100) (77GEP2757929). 4-Amino-5-formyl-3-methyltriazole and pentane-2,4-dione, set aside in 20% sulfuric acid, yielded 3,5-dimethyl-3//-l,2,3-triazolo [4,5-6] pyridin-6-yl... 

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