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16.12.4.1.4.8.4 Exchange of Oxygen for Sulfur

DOI: 10.1055/sos-SD-116-00063

von Angerer, S.Science of Synthesis Knowledge Updates, (20111426.

For certain purposes conversion of pyrimidinones into pyrimidinethiones is required, e.g. as starting materials for the preparation of (alkylsulfanyl)pyrimidines. Pyrimidinethiones 696 are obtained from the corresponding pyrimidinones by reaction with phosphorus pentasulfide.[‌156‌,‌894‌,‌1061‌,‌1067‌,‌1128‌‌1130‌] Hydroxy groups in the 5-position resist thionation whereas pyrimidin-4- and pyrimidin-6-ones are readily converted into thiones. Pyrimidin-2(1H)-ones react only under forcing conditions, but they are accessible by ring-closure reactions with thiourea in most cases (see, for example, Section 16.12.1.7.4.15.3). Thus, uracil yields selectively 4-thiouracil. Since the presence of a base increases both the yield and the reaction rate, pyridine is frequently used as solvent. Alternatively, sodium hydrogen carbonate can be added. Examples of the reaction conditions are given in Table 27.

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References


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