Synthesis and properties of p-benzoquinone-fused hexadehydro[18]annulenes

A series of hexadehydro[18]annulenes fused with different numbers of p-benzoquinone, 4-6, were synthesized by stepwise transformation of the p-dimethoxybenzene moiety of the precursor dehydroannulene 3 fused with three 3,6-dimethoxy-4,5-dimethylbenzene units at 1,2-positions into p-benzoquinone using ceric ammonium nitrate. The UV-vis spectra of compounds 4 and 5, which have both electron-donating p-dimethoxybenzene unit(s) and electron-accepting p-benzoquinone unit(s) in the π-systems, showed the maximum absorption bands bathochromically shifted in comparison with 3 having only p-dimethoxybenzene units and 6 having only p-benzoquinone units. However, the solvatochromism expected for 4 and 5 was found to be quite weak possibly because the HOMO and LUMO (B3LYP/6-31G(d)) are not localized but rather delocalized over the whole π-systems.     

Sulfonium ylides derived from 2-hydroxy-benzoquinones: crystal and molecular structure and their one-step conversion into Mannich bases by amine N-oxides

Reaction of 2-hydroxy-para-benzoquinones with DMSO/Ac₂O produced dimethylsulfonium ylides, of which crystal structures as well as solid and liquid state NMR spectra were recorded. The ylides react with tertiary methylamine N-oxides in a one-pot, multi-step process to 3-methylamino-substituted benzoquinones. The mechanism starts with a deoxygenative deprotonation of the amine N-oxides, followed by a formal electrophilic displacement of DMSO by the resulting carbonium-iminium ion.     

Qualitative and Quantitative LC Profile of Embelin and Rapanone in Selected Lysimachia Species

Qualitative and quantitative determination of the pharmacologically active benzoquinones, embelin and rapanone, in different organs of eight Lysimachia species has been conducted by reversed-phase high-performance liquid chromatography. An analytical Hypersil BDS C-18 column and a mobile phase of water containing 0.1% v/v H₃PO₄ and acetonitrile (10:90) at a flow rate of 1.0 mL min⁻¹ were used. UV detection was at 286 nm. The recovery of the method was 81.5% for embelin and 80.5% for rapanone. Good linearity (r > 0.999) was obtained for both compounds. The leaves of L. ephemerum had the highest amount of rapanone (1.69%) while the roots of L. punctata had the highest amount of embelin (1.28%).     

EFFICIENT,MULTIGRAM-SCALE SYNTHESIS OF THREE 2,5-DIHALOBENZOQUINONES

ABSTRACT

2,5-Dibromo-, 2,5-dichloro- and 2,5-diiodobenzoquinone were conveniently prepared from 1,4-dimethoxybenzene in 87%, 97% and 84% overall yields. None of the two steps of the synthesis required purification.     

Parvistemins A-D, a new type of dimeric phenylethyl benzoquinones from Stemona parviflora Wright

Four naturally occurring dimeric phenylethyl benzoquinones, parvistemins A-D, were isolated from the aerial parts of Stemona parviflora Wright. Their constitutions were established by spectroscopic methods. Due to restricted rotation about the central biaryl axis, the compounds are chiral, although racemic. Their two respective atropo-enantiomers were resolved by HPLC on a chiral phase and were stereochemically characterized online, in hyphenation with circular dichroism (CD) spectroscopy (LC-CD coupling), combined with quantum chemical CD calculations.     

Alkyl phenols from the wood of Averrhoa carambola

<正>Two alkyl phenols,namely,2,5-dimethoxy-3-undecylphenol(1) and 5-methoxy-3-undecylphenol(2),were isolated together with two known benzoquinones,5-O-methylembelin(3) and 2-dehydroxy-5-O-methylembelin(4) from the wood of Averrhoa carambola.Their structures were elucidated on the basis of spectroscopic methods(1D and 2D NMR).     

Theoretical and experimental interpretations of phenol oxidation by the hydroxyl radical

Phenol oxidation by OH radicals produced by the Fenton reaction was studied and the oxidation process was monitored by the UV–visible, ¹³C NMR and LC techniques. The results show that benzoquinone is formed. In the NMR and LC experiments, since the peaks corresponding to isomers ortho and para- benzoquinones are unresolved, DFT was used to determine the branching ratios of the isomers formation that coincides with their ΔG values (ortho > para > meta): 72% for ortho, 23% for para and 5.0% for meta. Furthermore, the energy profile of the OH attack at ortho is quite similar to that at the para position while the meta position attack is less favored by 2.0 kcal/mol.     

Formation of ATP by Photochemical Excitation of Benzoquinones in Dimethylacetamide Solution

A new method of adenosine triphosphate production is described which involves photo‐excitation of p‐benzoquinones under the presence of adenosine diphosphate and inorganic phosphate in N,N‐dimethylacetamide solution. A possible mechanism for the reaction is presented.     

Convenient oxidation of alkylated phenols and methoxytoluenes to antifungal 1,4-benzoquinones with hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3) catalytic system in neutral ionic liquid

Alkylated phenol and methoxytoluene derivatives were catalytically and selectively oxidized to the corresponding 1,4-benzoquinones in good conversions and yields. Reactions were performed with hydrogen peroxide (H₂O₂)/methyltrioxorhenium (CH₃ReO₃) in 1-butyl-3-methylimidazolium tetrafluoroborate [bmim]BF₄, a neutral ionic liquid. Compounds were tested in vitro for their antifungal activity against the growth of several widespread soil fungi. Some of them were proved to be potent inhibitors of Fusarium sp. than ketoconazole, a commercially available and expensive antifungal agent.     

PMR Spectra of Piperidine Involved in the Formation of Charge Transfer Complexes with 1,4-Benzoquinones

The proton magnetic resonance spectra of piperidine involved in the formation of charge transfer complexes with 1,4-benzoquinones, in chloroform, have been presented and discussed.