Synthesis and Reactivity of 5-Functionalized 4-Hydroxyhexahydropyrimidine-2- thiones/ones.

A new general two-steps synthesis of 5-functionalized 4-hydroxyhexahydropyrimidine-2-thiones/ones has been developed. This synthesis are based on preparation of the a-azido and a-tosyl(thio)ureas 2, 5 followed by reaction with enolates of a-functionally substituted ketones. All the obtained hydroxypyrimidines 8a-c are readily converted into the corresponding 5-functionalized 1,2,3,4-tetrahydrohydropyrimidine-2-thiones/ones 9a-c by heating in the presence of acids. Treatment of the 4-acylsubstituted 4-hydroxyhexahydropyrimidine-2-thiones/ones 8b with bases in acetonitrile gives the N-acyl-N'-(b-oxoalkyl)thioureas/ureas 10 in result of rearrangement including C(4)-C(5)-bond cleavage in 8b. Reaction of the (thio)ureides 10 and the 5-acylsubstituted 4-hydroxyhexahydropyrimidine-2-thiones/ones 8b with KOH in water leads to the 4-hydroxyhexahydropyrimidine-2-thiones/ones 11 without the acyl group at the C(5) position. Treatment of the ethyl 4-hydroxy-2-thioxohexahydropyrimidine-5-carboxylates 8a with bases in acetonitrile depending on the starting compounds structure yields either the 5,6-dihydro-2-thiouracils 12, 13 or the products of C(4)-C(5)-bond cleavage 14.