1.3- Dicarbonyl compounds, reaction with amidines

Heating diphenylcyclopropenone (DPP) with aryl amidoximes ArC(NH2)NOH gives pyrimidin-4-ones (225) this usefully supplements the previously reported reactions of DPP with amidines, which give dihydro-pyrimidin-4-ones. The previously mentioned /3-lactone (119) (see p. 240), which is an internally protected 1,3-dicarbonyl compound, reacts with acetamidine to give the pyrimidin-4-one (226). ... 

Numerous pyrimidines have been synthesized by reaction of a 1,3-dicarbonyl compound, or a potential 1,3-dicarbonyl compound, with an amidine representative substituents are shown in structures (241) and (242). 

Vogl and Taylor (378) first utilized the reaction of amidines, namely, a-amidino-a-aminoacetamide dihydrochloride (56, R = H) with a,0-dicarbonyl compounds to give 2-amino-3-carbamoylpyrazines (57, R = H). 

The reactions of amidines or guanidines with a-functionalized carbonyl compounds continue to be utilized for the synthesis of imidazoles. Thus, the mixed anhydride of acetic and chloroacetic acids reacts with symmetrical diarylguanidines to give l-aryl-2-arylaminoimidazolin-4-ones, and there is competitive formation of imidazoles and pyrimidines in the reaction of benzamidine with 3-bromobenzo-4-pyrones (18). Imidazoles are minor products, but are favored in nonpolar solvents. The use of a-dicarbonyl compounds with guanidine gives 2-amino-4-hydroxy-4-methyl-4//-imid-azoles, which give excellent yields of 2-aminoimidazoles on catalytic hydrogenation. " ... 

Trifluoroacetamidine (585) is most widely used for the principal synthesis of pyrimidines. Compound 585 can be prepared from ethyl trifluoroacetate by ammo-nolysis, followed by dehydration with P2O5 and reaction with ammonia (Scheme 124) [335,336]. Amidine 585 has been introduced into reaction with various p-dicarbonyl compounds and their synthetic equivalents (Table 27), including p-ketoesters (Entries 1-6), in particular p-ketopyruvates (Entry 3) and a-alkoxymethylene-p-ketoesters (Entries 4-6), p-enaminocarbonyl compounds (Entries 7-9), malonic acid derivatives (Entry 10), fluorinated p-diketones (Entry 11), vinamidinium salts (Entry 12), a,p-unsaturated nitriles with leaving group at p position (Entries 13-15) and other bis-electrophiles (Entries 16, 17). Usually, the reaction gives moderate yields of the target 2-CF3-pyrimidines (ca. 50 %). 

A range of NCN binucleophiles introduced into reaction with 700 is similar to that for fluorinated p-dicarbonyl compounds discussed in the previous section and includes amidines (Table 35, Entries 1, 2), (thio)urea and its derivatives (Entries 3-5), guanidines (Entry 6), semicarbazide derivatives (Entry 7), and electron-rich amino heterocycles (Entries 8-12). 

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