Über die σ‐Homologen des o‐Benzochinons

Abstract

Es wird die Darstellung und die Strukturbestimmung der beiden Isomeren des Bis-o-homoo-benzochinons 3 a und b und des um einen Cyclopropanring armeren Produkts 2 beschrieben; ihre Stereochemie wird erortert. Die Thermolyse von 3b ergibt als einziges Produkt Benzol. Die spektroskopischen Daten zeigen, daD 3 s und b keine, 2 nur in geringem MaDe chinoide Eigenschaften besitzen; 3 s und b sind cycloaliphatische Diketone. The a-Homologues of o-BenzoquinoneThe preparation and the determination of the structure of the two isomers of bis-u-homo-obenzoquinone 3 a and b and their mono-homo analogue 2 is described and their stereochemistry is discussed. The thermolysis of 3b yields benzene as single product. The spectroscopic data indicate that 3 a and b have no quinonoid properties while they are found to a small extent in 2. 3a and b are best described as cycloaliphatic diketones.Bisherige Untersuchungen an 1 lassen hierzu einen geringen Beitrag der Cyclopropylketon-Teilchromophore erkennen ; die Synthese des Bishomo-o-chinons 3 gewinnt zusatzliches Interesse dadurch, dal3 die Untersuchung der chinoiden Eigenschaften ') M.

Electrochemically-Induced Spirolactonization of α-(Methoxyphenoxy)alkanoic Acids into Quinone Ketals

“…These voltammogams are in agreement with an oxidation process consisting of an overall two-electron transfer from the aromatic nucleus in a generally accepted ECEC mechanism. 8a, Such a mechanism is thus initiated by a reversible electron tranfer (E) giving rise to an aryl radical cation which is irreversible trapped by a nucleophile such as the carboxylic unit of the substrate or methanol (C). The resulting radical, which should be more easily oxidized than the starting compound, is then immediately oxidized (E) to furnish an arenoxenium ion eventually quenched by a second nucleophilic trapping (C) (Scheme ).…”

“…Again, 1,2-bisalkyl aryl ethers such as 3 have been much less studied under anodic oxidation conditions than their 1,4-counterparts. To the best of our knowledge, the only reported case in the benzenoid series is the anodic oxidation of 1,2-dimethoxybenzene to 5,5,6,6-tetramethoxycyclohexa-1,3-diene, which thus demonstrated the feasibility of making orthoquinone bisketals by electrolysis aryl alkyl ethers in an alcoholic solvent 1 …”

Building Blocks of Eumelanin: Relative Stability and Excitation Energies of Tautomers of 5,6-Dihydroxyindole and 5,6-Indolequinone

“…The B3LYP excitation energies were slightly smaller for all states considered. The PBE0 results were in reasonable agreement with a measured spectrum of 4 in CHCl 3 which showed three maxima at 590 nm (2.10 eV, log ε =1.48), 375 nm (3.31 eV, log ε = 3.23), and 260 nm (4.77 eV, log ε = 3.11) . Clearly, a quantitative comparison of the energies corresponding to the maxima in the absorption spectra measured in solution with computational data for the vertical excitation energies is rather problematic.…”

“…The PBE0 results were in reasonable agreement with a measured spectrum of 4 in CHCl 3 which showed three maxima at 590 nm (2.10 eV, log )1.48), 375 nm (3.31 eV, log ) 3.23), and 260 nm (4.77 eV, log ) 3.11). 37 Clearly, a quantitative comparison of the energies corresponding to the maxima in the absorption spectra measured in solution with computational data for the vertical excitation energies is rather problematic. Nevertheless, our results for 4 seemed to be rather encouraging and indicative of possibility to utilize TD-DFT data for semiquantitative analysis of spectroscopic properties of 3.…”