1.3- Dimethyluracil table

Some oxidations of heterocyclcs with two heteroatoms proceed very readily. Thus, fluorinated quinazoline is oxidized to quinazol-4-one on fusing for only 2 minutes (Table 16).264 On the other hand, more vigorous oxidation of 5-fluoro-l,3-dimethyluracil by 3-chloroperoxybenzoic acid leads to the formation of unstable intermediate radicals that tend to rearrange to 4-hy-droxy-l,3-dimethylimidazoledione 3-chlorobenzoate (Table 16), similar177 to the chemical behavior of trifluoromethylated phenol.265... 

Palladium-based catalysts also bring about cyclopropanations in high-yield. With palladium acetate/CHjNj, styrene , unactivated terminal olefins strained olefins , 1,3-dienesan enamine , as well as a,3-unsaturated carbonyl compounds have been cyclopropanated (Table 1). Contrary to an earlier report, the reaction also works well with cyclohexene if the conditions are chosen appropriately it seems that the notniyst is rapidly deactivated in the presence of this olefin >. Trisubstituted a,p-unsaturated carbonyl compounds were found to be unreactive, and the same is true for the double bonds in diethyl fumarate, maleic anhydride, coumarin and 1,3-dimethyluracil. Whereas the latter two were totally unreactive, [3-1-2] cycloaddition of diazomethane gave pyrazolines in the former two cases. The last entry of Table 1 shows that an allyl alcohol function can still be cyclopropanated, but methylene insertion into the O—H bond is a competing process. 

The results shown in Table III indicate that the exclusive enol form of the 2 and 4 carbonyl groups in 2,4-diethoxypyrimidine leads to a fivefold decrease in reactivity. Alternatively, 1,3-dimethyluracil, which is in... 

Most unusual is the synthesis of y/c-triazolo[4,5-i/]pyrimidine (262) by heating 6-azido-l,3-dimethyluracil with potassium carbonate in DMF. Whereas intramolecular cyclization of an azide function onto C=N to give tetrazoles is well known, the corresponding formation of triazoles by addition to C=C is extremely rare. Also noteworthy are the 5-diazo-6-amino-uracils (263 R = Me, Et, or Ph), which, although table in boiling acetic acid, cyclize (with loss of nitrogen) in hot DMF to indolo[2,3-d]pyrimidines (264). Far superior are the photodecompositions of (263) which furnish the indolo-pyrimidines in quantitative yield. 

TABLE 105.1 Photolysis of 6-Chloro-l,3-dimethyluracil in Benzene in the Presence of Various Acids... 

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