1.3- Dimethylbarbituric acid, formation

A related pyranopyrimidine 63 has been prepared by the irradiation of 1,3-dimethylbarbituric acid 61, a methylene active nitrile 47a and N,N-di-methylformamide dimethylacetal 45 [77]. After initial formation of the enam-... 

The anodic oxidation of catechol in the presence of 1,3-dimethylbarbituric acid was carried out in aqueous solution containing sodium acetate in an undivided cell at graphite and nickel hydroxide electrodes [114]. The results did not fit with the expected structure (Scheme 47, path A) but a dis-piropyrimidine was isolated in 35% yield (Scheme 47, path B). It seems that the initial attack of 1,3-dimethylbarbituric acid on the anodically formed o-quinone does not occur through the carbon-oxygen bond formation but rather through the carbon-carbon bond formation, giving rise to the final product via several consecutive reaction steps. 

By using the same catalytic system, alkylations of 1,3-dimethylbarbituric acid with alcohols were also accomplished (Scheme 5.31) [68]. The Cp lr-catalyzed alkylation using 2-iodobenzyl alcohol, followed by palladium-catalyzed carbon-carbon bond formation with allene, gave spirocyclic barbituric acid derivatives in a one-pot process. 

Dimethylcyclohexane-l,3-dione (dimedone) and Ai,Ai-dimethylbarbituric acid are relatively acidic (3-dicarbonyl compounds 5.3 and 4.7, respectively). The deprotection reaction involves (Scheme 16) a prototropic equihbrium between the P-dicarbonyl compounds and the deprotected carbamate species (shifted further to right by the formation of carbon dioxide and the respective amine). 

The S5mthesis of furopyrimidines has received a little attention in spite of their wide range of associated bioactivities including antimicrobial, antiviral, antimicotic, and antiplatelet [84-86]. Shaabani et al. reported a three-component condensation reaction of N,N -dimethylbarbituric acid with aldehydes and alkyl or aryl isocyanides at room temperature (RT) in the presence of [BMIM][Br] in a molar ratio of 1 1 (reactant/IL) to afford furo[2,3-d]pyrimidine-2,4(lH,3H)-diones 32 (Scheme 6). The authors cited that the presence of an electron-withdrawing group was necessary and addition of [BMIM][Br] was crucial for the formation of the desired product in high yield [87]. 

---