作者:O. B. Safonova、D. V. Kravchenko、I. N. Senchenya、V. F.Traven'
DOI:10.1023/a:1012331118017
日期:——
Tautomeric transformations of 4-methyldihydrofuro[2,3-h]coumarin-9-one and its 8-substituted derivatives were studied by H-1 NMR, electronic absorption spectroscopy, and quantum chemistry. The 1H NMR spectra of these compounds in CDCl3 show that they exist in the ketone form, and in more polar solvents they can pass into the enol form. By electronic absorption spectroscopy it was established that the derivatives containing electron-acceptor substituents in the 8 position of the furanone ring undergo tautomeric transformations as the composition of the solvent is varied from 100% methanol to 100% CCl4. At the same time, the derivatives with electron-donor substituents in the same position do not show any specific alterations in the absorption spectra with solvent. Analogous pattern was observed in the enolization Or Substituted dihydrofurocoumarinones by acetylation: In presence of electron-donor substituents in the 8 position, no acetylation occurred, while with the compounds containing electron-acceptor substituents, the corresponding 9-acetoxy-4-methylangelicins were prepared in high yields. Calculations by the PPP/CI method of the electronic absorption spectra 4-methyldihydrofuro[2,3-h]coumarin-9-one showed that in polar solvents (methanol) it prefers the enol form. Data of spectral measurements were compared with results of semiempirical (MNDO, AM1, and PM3) and nonempirical quantum-chemical calculations (with 3-21G, 6-31G*, and 31G** basis sets).