Quantum chemical studies of pyrimidin-4-ones Part 6. On peculiarities of the reactions with nitrating agents of some carboxylic acids of the thieno[2,3-d]pyrimidin-4-one series and their esters

Abstract

Quantum chemical calculations of the energies, electronic structures, and molecular geometries of 5-methyl-, 2,5-dimethyl-, 3,5-dimethyl-, and 2,3,5-trimethyl-4-oxothieno[2,3-d]pyrimidine-6-carboxylic acids; 5-methyland 3,5-dimethyl-2,4-dioxothieno[2,3-d]pyrimidine6-carboxylic acids; 5-methyland 3,5-dimethyl-4-oxo-2-thiothieno[2,3-d]pyrimidine-6-carboxylic acids; and their ethyl esters were performed in terms of the HF and DFT (B3LYP) approximations in the 3-21G basis set. The reactions routes with nitrating agents were examined, and the factors governing the direction of the reactions, the probability of their occurrence were determined. Selective ipso-substitution of the 5-methyl group by the nitro group at the C(5) atom of the thiophene fragment is hindered for all compounds studied. The reasons for the unfavorable ipso-substitution were discussed taking into account effects of solvents and substituents in positions 2, 3, and 6 of 6-carboxyand 6-ethoxycarbonyl-substituted thieno[2,3-d]pyrimidin-4-ones.