The structure of benzoyldimedone from X-ray diffraction analysis

Abstract

The structure of benzoyldimedone was established by X-ray diffraction analysis. The only tautomer was found. In this tautomer, the enol proton is covalently bound to the oxygen atom that is remote from the phenyl group. The role of steric and electronic factors in stabilization of the enol structure is analyzed. The geometric characteristics of the ring formed through an intramolecular hydrogen bond are discussed.Key words: X-ray diffraction analysis, tautomerism, intramolecular hydrogen bond, ]3-dike/ones, [3-triketones, conjugation, 2-benzoyl-5,5-dimethylcyclohexane-1,3-dione.13-Diketones and 13-triketones attract attention of researchers t'z because of their use in synthetic practice, including the synthesis of biologically active compounds, and the presence of the keto-enol and enol-enol tautomerism. Besides, the enol tautomers of these compounds were found to have a strong intramolecular hydrogen bond. The tautomeric properties and the presence of the H bond are responsible for the high lability of the structures and high reactivities of these compounds both when substituents are introduced and when the temperature and the solvent are varied. The regularities of the influence of these factors on the enol tautomers and their structures remain in many respects unclear.NMR spectral studies demonstrated 3 that in the case of acetyldimedone, unlike acetylacetone, 2 the replacement of the methyl group by the phenyl fragment leads to a shift of the enol-enol tautomeric equilibrium toward the tautomer containing the enol proton at the O atom that is remote from the phenyl group. Previously, 4 based on the data of low-temperature neutron diffraction study, s it has been concluded that there is only one potential well for the H bond in the benzoylacetone molecule. This conclusion is inconsistent with abundant data on the structures of [3-diketones 2 and is, apparently, somewhat untimely. The structures of [3-diketones have been studied in detail by X-ray and neutron diffraction analysis. 6-13 The structures of ~-triketones have been studied only in two works. 14.t5 In this work, the structure of the benzoyldimedone molecule was studied by X-ray diffraction analysis. ExperimentalSingle crystals of 2-benzoyl-5,5-dimethylcyclohexane-1.3-dione were prepared by slow evaporation from a 1 : I ether--hexane mixture with cooling to ~10 ~ A crystal of dimensions 0.8• mm was chosen for X-ray diffraction study. The three-dimensional X-ray diffraction data set was collected on an a~ztomated four-circle Nicolet R3m diffractometer (Mo-Kct radiation, graphite monochromator. (based on all data). All calculations were carried out using the SHELX-97 program package. 16-Is The atomic coordinates, bond lengths, and bond angles of the fS-triketone were deposited with the Cambridge Structural Database.

Mode of Action of 4-Hydroxyphenylpyruvate Dioxygenase Inhibition by Triketone-type Inhibitors

“…From the X-ray crystallographic analysis shown in Figure , compound 1 in the crystal exists only as the cis−enol tautomer with an intramolecular hydrogen bond. In this tautomer, the enol hydrogen is covalently bound to the oxygen atom that is remote from the phenyl group, which is similar to the structure of benzoyldimedone reported recently by Borisov . It is clear that the 1,3-diketone and the 2-carbonyl moiety of 1 are coplanar and conjugated by hydrogen bonding of the C-3 enolic hydrogen to the oxygen atom of the C-2 carbonyl group with a torsional angle of 1.6°.…”

“…In this tautomer, the enol hydrogen is covalently bound to the oxygen atom that is remote from the phenyl group, which is similar to the structure of benzoyldimedone reported recently by Borisov. 13 It is clear that the 1,3diketone and the 2-carbonyl moiety of 1 are coplanar and conjugated by hydrogen bonding of the C-3 enolic hydrogen to the oxygen atom of the C-2 carbonyl group with a torsional angle of 1.6°. If one of the carbonyl groups in the triketone is modified, however, the inhibition potency of the resulting compound decreases substantially.…”

Three-dimensional QSAR of HPPD inhibitors, PSA inhibitors, and anxiolytic agents: Effect of tautomerism on the CoMFA models

“…Twenty one compounds containing acyl-cyclohexan-2-one structural fragment and their HPPD inhibitory potencies, expressed as pIC 50 (M), are listed in Table 1. These compounds, especially those possessing acyl-cyclohexan-1,3-dione skeleton, have many possible tautomeric forms, of which two, as shown in Table 1, have been identified by different techniques to exist [16,[32][33][34]. While theoretical calculations carried out by us [32], crystallography data [16,33] as well as the NMR experiments in CDCl 3 solution [34] suggested that the endocyclic enol-tautomer (II) was slightly predominant for compounds of this type, a later NMR study [35] revealed that one of these compounds, 2-[2-nitro-4-(triflouromethyl)benzoyl]-1,3-cyclohexanedione (NTBC, H9), existed solely as exocyclic enol-form (I) in aqueous solution at pH 7.0.…”

Synthesis of new bicyclo[4.1.0]heptane-2,4-dione derivatives and their herbicidal activity

“…Spectral data are listed in Table 1. As for the structure of the benzene substituted triketones, it has been reported by Borisov et al 12) and Wu et al 13) that these compounds exist as a cis-enol tautomer with an intramolecular hydrogen bond. The triketone compounds such as 10a mentioned in this article also suggested that there existed two enol-form isomers 10a-I and 10a-II (Fig.…”