Synthesis of diethyl 2-thioxo-1,2,3,4-tetrahydroand hexahydropyrimidine-5-phosphonates

The reaction of sodium enolate of diethyl (2-oxoprop-1-yl)phosphonate with N-(1-tosylprop-1-yl)thiourea results in the stereoselective formation of diethyl (4R*,5R*,6R*)-6-ethyl-4-hydroxy-4-methyl-2-thioxohexahydropyrimidine-5-phosphonate, which is transformed into diethyl 4-ethyl-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-phosphonate and diethyl (4R*,5S*,6R*)-4-ethyl-6-methyl-2-thioxohexahydropyrimidine-5-phosphonate by acid-catalysed dehydration and stereoselective reduction with NaBH₄–CF₃COOH, respectively.