Microwave-Facilitated Synthesis of Pyrimidinones

Significance

Reported is the microwave-facilitated synthesis of a series of 3,4-dihydroxy-2-alkoxy-6-benzyl-4-oxopyrimidines (DABOs). The process was optimized for the formation of S-DABO using S-methylisothiourea sulfate and then extended to the synthesis of N-DABOs using substituted guanidinium salts. The reaction is proposed to proceed by initial Michael-type addition of the thiourea or guanidine into the butynoate to give an intermediate of the general structure A, which upon cyclization would lead to the observed products. Isolation of the intermediate A provided support for this mechanism; however, yield or characterization data for this compound was absent from the otherwise good supporting information.