ENOLETHERS .21. SYNTHESIS OF 5,5'-DISUBSTITUTED 4,4'-BIPYRIMIDINES

1,6-Dialkoxy-3,4-diones 3 are easily accessible by acylation of enol ethers 1 with oxalyl chloride and subsequent elimination of hydrogen chloride using triethylamine. The open-chain 2,5-dimethyl derivative 3b is converted with amidines 4a-c and S-methylisothiourea (4d), respectively, to give 2,2'-disubstituted 5,5'-dimethyl-4,4'-bipyrimidines 5a-d. The dihydrofuran and dihydropyran derivatives 3c and 3d, however, react with benzamidine (4c) in dimethylformamide only in the presence of calcium hydride as condensation agent yielding 5,5'-bis(2-hydroxyethyl)- and 5,5'-bis(3-hydroxypropyl)-2,2'-diphenyl-4,4'-bipyrimidine 6a and b.