58870-09-0Relevant articles and documents
Dynamic NMR Investigation of the Annular Tautomerism in Dihydropyrimidines
Weis, A. L.,Porat, Z.,Luz, Z.
, p. 8021 - 8024 (1984)
1H and 13C NMRspectra of 6-methyl-2,4-diphenyl-1,4-dihydropyrimidine (MDHP) in several organic solvents are reported.In dilute solutions of purified solvents, separate NMR signals from the two tautomeric forms, 1,4-MDHP (A) and 1,6-MDHP (B), are observed.From the relative intensities of the peaks, the equilibrium constant K / has been determined in CDCl3, dioxane, Me2SO, and HMPA.In impure solvents and/or a high concentration of MDHP there is fast tautomeric equilibrium between forms A and B, and only a single, average set of peaks is observed.The kinetics of the tautomeric process and its dependence on temperature and MDHP concentration in purified CDCl3 solvent was quantitatively studied by 1H NMR line-shape analysis.The results indicate that two mechanisms contribute to the reaction, (i) a monomolecular process characterized by the kinetic parameters k1(300 K) = 31 +/- 4 s-1 and ΔE* = 4.5 +/- 0.6 kcal/mol and (ii) a bimolecular reaction with k2(300 K) = (1.0+/- 0.2)103 M-1 s-1 and ΔE* = 3.3 +/- 0.7 kcal/mol.
Crystal and Molecular Structure of 6-Methyl-2,4-diphenyl-1,4-dihydropyrimidine
Weis, Alexander,Frolow, Felix
, p. 89 - 90 (1982)
An X-ray crystallographic study of 6-methyl-2,4-diphenyldihydropyrimidine (1) has shown that in the solid state it exists in the 1,4-dihydro-form (1a) with a flat boat conformation, as single tautomeric entity.
Dihydropyrimidines. Part 6. 5-Acetyldihydropyrimidines via Condensation of Olefinic Acetylacetones with Amidines. Reinvestigation of Ruhemann's Reaction.
Weis, Alexander L.,Frolow, Felix
, p. 83 - 90 (2007/10/02)
The condensation of benzylideneacetylacetone and benzylamidine, studied by Ruhemann in 1903, has been reinvestigated in detail, and several new reaction products have been isolated and identified.The influence of varying the conditions of reaction have been studied.By using an aprotic solvent (benzene) with azeotropic removal of the water released, for example, the reaction is directed towards formation of 5-acetyldihydropyrimidine (5a).This compound has been obtained in better yields with a two-step approach: initial preparation of the 5-acetyl-6-hydroxytetrahydropyrimidine intermediate (4a), followed by dehydration in acidic media.While this tetrahydropyrimidine in CDCl3 solution most probablyexists as a mixture of the 1,4,5,6-tetrahydro and 3,4,5,6-tetrahydro compounds, crystallization from acetone gave single crystals of 5-acetyl-6-hydroxy-3,4,5,6-tetrahydropyrimidine (4aB) and water in the ratio 2:1.Using the two-step procedure, other tetrahydro- and dihydro-pyrimidine derivatives have been prepared from m-nitrobenzylideneacetylacetone and benzamidine.The reaction has also been explored using acetamidine.All isolated 5-acetyldihydropyrimidines exist in the solid state in the 1,4-dihydro form.However, in solution amidinic tautomerism was observed, which also favours the 1,4-dihydro tautomer.These newly prepared dihydropyrimidines easily undergo oxidation to the corresponding pyrimidines The mechanism of the basic deacetylation observed by Ruhemann in ethanolic solutions, affording the 5-unsubstituted dihydropyrimidine, is also discussed.
