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Synthesis 1988; 1988(10): 816-820
DOI: 10.1055/s-1988-27720
DOI: 10.1055/s-1988-27720
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Synthesis of Thiazolo[3,2-a]pyrimidines and Oxazolo[3,2-a] pyrimidinium Salts from 3-Isothiocyanato-2-propeniminium Salts and α-Aminocarbonyl Compounds
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Publication History
Publication Date:
12 September 2002 (online)
The easily available 3-isothiocyanato-2-propeniminium salts 2 react with α-aminoacetophenone or ethyl glycinate to give 1-phenacyl-2-thioxo-1,2-dihydropyrimidines 4 or 1-ethoxycarbonylmethyl-2-thioxo-1,2-dihydropyrimidines 6, respectively. Compounds 4 can be directly cyclized to thiazolo[3,2-a]pyrimidinium salts 5. Compounds 6 are first submitted to alkaline hydrolysis and the resultant free acids 7 cyclized to the mesoionic thiazolo[3,2-a]pyrimidine derivatives 8 by reaction with carboxylic anhydrides. S-Methylation of compounds 4 followed by base-catalyzed elimination of methanethiol affords oxazolo[3,2-a]pyrimidinium salts 10.