A new regioselective synthesis of 5- and 6-aryluracil bases based on direct C-H arylations of diverse 1,3-protected uracils has been developed. Benzyl-protected uracils were selected as the most practical in terms of stability during the arylation and facile cleavage of the benzyl groups. Pd-catalyzed C-H arylations in the absence of CuI gave preferentially 5-aryl-, whereas the reactions in the presence of CuI gave 6-aryl-1,3-dibenzyluracils. Final deprotection either by transfer hydrogenolysis over Pd/C or by treatment with BBr(3) gave the desired free arylated uracil bases in good yields.
A novel efficient synthesis of 2,4-diarylpyrimidines was developed based on phosphonium-mediated Suzuki coupling of 2-(methylsulfanyl)pyrimidin-4(3H)-one (at position 4) followed by the Liebeskind-Srogl cross-coupling (at position 2) under microwave irradiation.
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