Pyrimido pyrimidine-2,4-diones synthesis

Pyrimido[4,5-d]pyrimidine-5,7-diones synthesis, 3, 363 Pyrimidopyrimi dines synthesis, 4, 507 Pyrimido[ 1,2-a]pyrimidines reaetivity, 3, 348 strueture, 3, 337-338 synthesis, 3, 360 Pyrimido[ 1,6-a]pyrimidines reaetivity, 3, 349 structure, 3, 338 synthesis, 3, 362 Pyrimido[l, 6-c]pyrimidines reaetivity, 3, 349 strueture, 3, 338 synthesis, 3, 362 Py rimi do[4,5-djpyri midi nes applieations, 3, 368 eleavage, 3, 350 reaetions... 

Pyrimido[4,5-d]pyrimidine-2,4-dione, 5-amino-7-methylthio-synthesis, 3, 364... 

Selective reduction of the 7-oxo group in pyrido[23-synthetic approach to 5,10-dideazatetrahydrofolic acid <00H(53)1207>. Cycloaddition of pyrimido[4,5-c][l,2,5]oxadiazine 96 with 2,3-dihydrofuran affords a new synthesis of dimethyllumazine derivative 97 which undergoes a ring-opening reaction to give pyrazine derivative 98 <00JHC419>. 

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). 

Solid-phase syntheses of pyrimidines continue to appear at a rapid pace. A solid-phase synthesis of 4-(2-amino-6-phenylpyrimidin-4-yl)benzamide was directly scaled up in excellent yields and high purity <03OPRD553>. The synthesis of imidazo[l,2-a]pyrimidines 59 via condensation of a solid-supported a-bromoketone and 2-aminopyridines was reported <03TL6265>. Pyrimido[4,5-t/]pyrimidine-2,4(l//,3W) diones have been accessed via a versatile solid-phase synthetic route <03S1739>. A microwave-assisted solid support synthesis of 5-methyl-6-ethylcarboxyIate-2-thioxothieno[3,2-iflpyrimidine-4(l//)-ones from 2-amino-3,5-diethyl carboxylate-4-methylthiophene and monosubstituted thioureas was reported <03BKC1038>. 

A novel and versatile solid-phase synthesis of pyrimido[4,5- fJpyrimidine-2,4-diones has been reported <03S1739>. The key step is the reaction of the support-bound pyrimidine with isocyanates, involving formation of a carbamate intermediate, followed by a base-catalyzed intramolecular ring closure to give the polymer-bound pyrimidopyrimidines which are used in subsequent reactions providing 1,3-disubstituted 7-amino derivatives. 

Pyrimido [4,5-d] pyrimidin-2,5-dione 150 were s)mthesized from DHPMs through a protocol, which involved the synthesis of N-3 substituted derivatives (Scheme 57). When 4 (R = Et, R = OEt, R = H, X = O, R = 2-Cl) was reacted with freshly prepared 4-chlorophenyldiazonium chloride 147 in cone. HCl, N-3 148 was obtained. Refluxing with various arylthioureas 149 and subsequently reaction with sodium methoxide in methanol at 0 °C gave 150 (04BMC4185). 

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