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The yield orotic aldehyde at the oxidation of 6-methyl-2,4-dihydroxypyrimidine was found to increase when selenious acid is used as an oxidizer. A comparative analysis of 6-methyl-2,4-dioxypyrimidine oxidation with selenium dioxide and selenious acid was performed using the ab initio quantum chemical method in the 6-31G** basis.

Reactions of 5-benzylidene-2-thioxo-2,3-dihydro-(1H,5H)-pyrimidine-4,6-diones with a singlet difluorocarbene afford difluoromethoxy derivatives in 20–34% yield. The quantum-chemical analysis of the reaction mechanism showed that N,N-dimethylformamide is involved into the formation of difluoromethoxy derivatives.

The electronic structure of the starting, intermediate, and final compounds was studied by MNDO calcualtions with the Dewar and Thiel parameters [2]. As follows from the calculations, the most probable reaction pathway involves initial formation of (dimethoxyphosphinoyl)methanol (VI). Energetically, the most advantageous participant of the acid-catalyzed reaction is a five-coordinate phosphorus phosphite structure that forms with II an energetically favorable transition state VII. DOI: 10.1134/S1070363208070335