Vk. Ahluwalia et R. Sahay, SYNTHESIS OF 1,3-DIARYL-1,2,3,4-TETRAHYDRO-7-METHYL-4, 5-DIOXO-2-THIOXO-5H-PYRANO[2,3-D]PYRIMIDINES, Indian journal of chemistry. Sect. B: organic chemistry, including medical chemistry, 35(3), 1996, pp. 248-250
Claisen condensation of 5-acetyl-1, 3-diaryl-1, 3-diaryl-1, 3-dihydro-
6-hydroxy-4-oxo-2-thioxopyrimidines (1a-f) with ethyl acetate affords
1, 3-diaryl-1, 3-dihydro-6-hydroxy-4-oxo-5-(1, 3-dioxobutyl)-2-thioxop
yrimidines (2a-f) which on heating in glacial acetic acid in the prese
nce of phosphorus pentoxide furnish the title compounds (3a-f).