Highly selective synthesis of triptycene o-quinone derivatives and their optical and electrochemical properties

A convenient and efficient method for the selective synthesis of a series of triptycene o-quinone derivatives is described. The triptycene o-quinones, especially the ones containing the methoxy group(s) (electron donor) and the o-quinone group(s) (electron acceptor) simultaneously, show interesting intramolecular CT interactions and electrochemical properties. Moreover, DFT calculations display that introducing a strong electron-donor group into triptycene o-quinone results in an increasing of the HOMO energy level, which subsequently decreases the HOMO-LUMO energy gap.     

Base-catalyzed Schmittel cycloisomerization of o-phenylenediyne-linked bis(arenol)s to indeno[1,2-c]chromenes

We describe the transition metal-free base-catalyzed Schmittel cycloisomerization reactions of o-phenylene-linked bis(arenol)s to indeno[1,2-c]chromene derivatives through prototropic rearrangement (tautomerization) to a putative vinylidene o-quinone methide intermediate with an enyne-allene system followed by a formal inverse-electron-demand hetero Diels–Alder cycloaddition. The preliminary results on catalytic asymmetric cycloisomerization with chiral bases are also disclosed.     

Mild and rapid method for the generation of o-quinone methide intermediates. Synthesis of puupehedione analogues

A route to simpler analogues to bioactive puupehedione derivatives involving a hetero Diels-Alder cycloaddition of a o-quinone methide is described. These intermediate species are generated via fluoride-induced desilylation of silyl derivatives of o-hydroxybenzyl iodides. Remarkable short reaction times and very mild experimental conditions are the main features of this method.     

Oxidative chemistry of the natural antioxidant hydroxytyrosol: hydrogen peroxide-dependent hydroxylation and hydroxyquinone/o-quinone coupling pathways

Oxidation of the natural antioxidant hydroxytyrosol (1) with peroxidase/H₂O₂ in phosphate buffer at pH 7.4 led to the formation of two main ethyl acetate-extractable products. These could be isolated by preparative TLC after reduction and acetylation, and were identified as the tetraacetyl derivative of 2-(2,4,5-trihydroxyphenyl)ethanol (3) and the heptaacetyl derivative of the pentahydroxybiphenyl 4 by 2D NMR and MS analysis. Similar oxidation of 4-methylcatechol gave, after the same work-up, the acetylated derivatives of 1,2,4-trihydroxy-5-methylbenzene (5) and the pentahydroxybiphenyl 6. Mechanistic experiments suggested that hydrogen peroxide affects the course of the oxidation of 1 by adding to the first formed o-quinone to give a hydroxyquinone intermediate. This could bring nucleophilic attack to the o-quinone of 1 to give the dimer 4. These results disclose novel oxidative pathways of 4-alkylcatechols and provide an improved chemical basis to enquire into the mechanism of the antioxidant action of 1.     

A simple specific test for inner-ring o-quinones

A simple specific test for inner-ring o-quinones is introduced. The test consists of the reaction of the quinone with 3,4-dimethoxyamline in hot acetic acid to give dye(s) absorbing near 600 mμ Spot test and colorimetric rnoditications of the test are described Other types of quinones and ketonic compounds give negative results The spectra of the o-quinones in sulfuric acid are also presentedWith the new method, fairly specific tests are now available for (a) inner-ring p-quinones, (b) inner-ring o-quinones, and (c) terminal ring o- and p-quinones     

Novel method for the synthesis of functionalized tetrathiafulvalenes, an acceptor-donor-acceptor molecule comprising of two o-quinone moieties linked by a TTF bridge

In search of a synthesis of o-quinone-tetrathiafulvalene-o-quinone triads a novel facile route was developed. Sodium tetrathiooxalate was for the first time used as a synthon in functionalized TTF preparation. The main purpose of this work was to construct an organic compound, which on the one hand possesses a redox-amphotericity, and on the other hand can act as a bridging ligand in construction of linear, 2D and 3D assemblies. Properties of new acceptor-donor-acceptor ligand in respect to application as a building block for the molecular devices have been investigated.     

Synthesis of new carbonyl and fluoroalkyl o-quinone methides from β-lapachone

The synthesis of new carbonyl and fluoroalkyl o-quinone methides from β-lapachone is reported.     

Hydrothermal synthesis and crystal structure of a new molybdenum oxide compound with manganese-o-phen subunit: [Mn(o−phen)(H2O)MoO4]·H2O (o-phen=o-phenanthroline)

A new one-dimensional molybdenum oxide compound with manganese-o-phen subunit: [Mn(o-phen)(H₂O)MoO₄]·H₂O (1) (o-phen=o-phenanthroline) was synthesized by thehydrothermal reaction of Na₂MoO₄·2H₂O, MnSO₄·H₂O, oxalic acid, o-phenanthroline (o-phen) and water. Its structure was determined by elemental analyses, ESR spectrum, TG analysis, IR spectrum and single-crystal X-ray diffraction. Compound 1 crystallizes in triclinic system, space group P-1 with a=7.0401(2) Å, b=10.4498(2) Å, c=10.5720(2) Å, α=73.26(7)°, β=83.34(8)°, γ=77.33(9)°, V=725.5089(0) Å³, Z=2, and R₁=0.0322 for 2337 observed reflections. Compound 1 exhibits one-dimensional chain structure. The chains are linked up via hydrogen bonding to 2D layers, which are further assembled through π-π stacking interactions to a 3D supermolecular structure.     

A layered vanadium arsenate network decorated with the directly coordinated organonitrogen ligands: [V4O7(HAsO4)2(o-phen)2] (o-phen=o-phenanthroline)

A novel layered vanadium arsenate [V₄O₇(HAsO₄)₂(o-phen)₂] 1 (o-phen=o-phenanthroline) was synthesized by the hydrothermal reaction of V₂O₅, ZnCl₂, Na₂HAsO₄·7H₂O, o-phenanthroline (o-phen) and water. Its structure was determined by elemental analyses, ESR spectrum, XPS spectrum, TG analysis, IR spectrum and the single-crystal X-ray diffraction. Compound 1 crystallizes in monoclinic system, space group P2/c, a=10.122(2) Å, b=9.867(2) Å, c=15.367(3) Å, β=102.83(3)°, V=1496.4(5) Å³, Z=1, λ(MoKα)=0.71073 Å, (R(F)=0.0397 for 3422 reflections). Data were collected on a Rigaku R-AXIS RAPID IP diffractometer at 293 K in the range of 2.06°<θ<27.48°. The title compound contains an unusual two-dimensional (2D) As-V-O layer with four-, six- and eight-membered rings. The chelating o-phen ligands project perpendicularly above and below the undulating layer. 1 represents the first example of 2D inorganic vanadium arsenate backbone grafted with the directly coordinated organic ligands. Furthermore, the 3D supermolecular architecture is formed by π-π stacking interactions of the o-phen groups between adjacent layers.     

o-Quinone methide based approach to isoflavans: application to the total syntheses of equol, 3′-hydroxyequol and vestitol

A concise strategy is developed for the synthesis of isoflavans employing a Diels-Alder reaction between o-quinone methides and aryl-substituted enol ethers followed by reductive cleavage of the acetal group. The method is extended towards the total syntheses of equol, 3′-hydroxyequol and vestitol.     

Enantioselective organocatalytic aryloxylation of aldehydes with o-quinones

An enantioselective organocatalytic inverse electron demand hetero Diels-Alder reaction of in situ generated enamines with o-quinone reagents is reported. The method, which is optimal in wet acetonitrile at ambient temperature, provides a new and direct asymmetric route to the aryl alkyl ether motif and an alternative metal-free strategy to S_N2 substitutions with phenolate nucleophiles.     

Iptycene quinones: synthesis and structure

A practical and efficient method to synthesize iptycene quinones has been developed. As a result, a series of pentiptycene quinones 8-16 were conveniently synthesized by one-pot reaction of triptycene quinone 4 or 5 with anthracene 1 or its derivatives 2-3 in refluxing acetic acid in the presence of p-chloranil, followed by CAN oxidative demethylation. Similarly, a series of heptiptycene quinones 17-23 with U-shaped cavities were achieved with pentiptycene quinone 10 and triptycene diquinone 6 as precursors. Non-iptycene triquinones 24 with one tweezer-shaped cavity and 25 with two U-shaped cavities were synthesized by one-pot reactions of anthracene with pentiptycene triquinones 16a and 16b, respectively. Non-iptycene triquinone 26 with a dendritic structure was conveniently obtained by the reaction of anthracene with either pentiptycene diquinone 12 or triptycene triquinone 7. The structures of regioisomers 16a and 16b were determined by the single-crystal structure analysis of 16b. The structures of other regioisomers, including heptiptycene tetraquinones 19a/19b/19c and heptiptycene triquinones 23a/23b, were identified by comparative reactions.     

Production of theasinensins A and D, epigallocatechin gallate dimers of black tea, by oxidation-reduction dismutation of dehydrotheasinensin A

Theasinensins A and D are B,B′-linked dimers of (−)-epigallocatechin 3-O-gallate connected through R and S biphenyl bonds, respectively, and are major constituents of black tea. Enzymatic oxidation of epigallocatechin 3-O-gallate produced dehydrotheasinensin A, and the structure was shown to be equivalent to an o-quinone of theasinensin A. When the aqueous solution of dehydrotheasinensin A was heated, theasinensin D was produced along with galloyl oolongtheanin. On the other hand, dehydrotheasinensin A was converted to theasinensins A and D along with oxidation products in phosphate buffer at pH 6.8 at room temperature. The results strongly suggested that theasinensins in black tea were produced by oxidation-reduction dismutation of dehydrotheasinensin.     

Reversal of the regioselectivity in a cycloaddition of o-quinones by varying the position of alkoxy substituents

We have investigated the regioselective cycloaddition of o-quinones 1b-e with the protected sinapyl alcohol 2. It was found that the position of the alkoxy substituent on the o-quinone ring controlled the regioselectivity of the cycloaddition. In addition, our reported procedure for determining the location of the side chains on 1,4-benzodioxanes has been improved.     

Cyclization and oxidation of o-bromophenylacetamides for the synthesis of oxindoles and isoindigoes

N-substituted oxindoles were obtained through a facile KOH/DMSO promoted intramolecular cyclization of o-bromophenylacetamides in good yields. Furthermore, isoindigo derivatives were readily synthesized through sequential intramolecular cyclization, oxidation and condensation of o-bromophenylacetamide in the presence of copper (II) acetate monohydrate, iodobenzene diacetate and KOH/DMSO. This method provides a convenient synthesis of a range of oxindoles and symmetrical biologically important (E)-bisindole-2-ones using o-bromophenylacetamide as sole starting material. The reaction mechanism is elucidated in light of the control experiment results.     

A general asymmetric route to enantio-enriched isoflavanes via an organocatalytic annulation of o-quinone methides and aldehydes

Reported herein is a general approach to optically active isoflavanes based on a chiral amine-catalyzed [4?+?2] asymmetric annulation of o-quinone methides and aldehydes. A number of naturally occurring isoflavanes, including equol, sativan, isosativan, vestitol and medicarpin, as well as isoflavane analogues were readily prepared with good to excellent enantioselectivities.     

Synthesis of 2-substituted-benzothiazoles by palladium-catalyzed intramolecular cyclization of o-bromophenylthioureas and o-bromophenylthioamides

2-Amino-, and 2-alkyl-benzothiazoles have been efficiently prepared by palladium catalyzed cyclization of o-bromophenylthioureas and o-bromophenylthiamides. Results were best with the Pd₂(dba)₃/monophosphine catalytic system.     

Dehalogenation of o-dihalogen substituted arenes and α,α′-dihalogen substituted o-xylenes with lanthanum metal

It was found that lanthanum metal caused the dehalogenation of o-dihalogen substituted arenes and α,α′-dihalogen substituted o-xylenes to generate the corresponding benzynes and o-quinodimethanes. When o-dihalogen substituted arenes were allowed to react with lanthanum metal in the presence of dienes, the Diels-Alder products between benzyne and dienes were formed in moderate to good yields. Similarly, the Diels-Alder adducts of o-quinodimethane with dienophiles were obtained, in the reaction of α,α′-dibromo-o-xylenes with lanthanum metal in the presence of dienophiles.     

Iron-catalyzed cascade reaction of ynone with o-aminoaryl compounds: a Michael addition-cyclization approach to 3-carbonyl quinolines

An efficient iron-catalyzed cascade Michael addition-cyclization of o-aminoaryl compounds including o-aminoaryl aldehydes, o-aminoaryl ketones, and o-aminobenzyl alcohols with ynones for the synthesis of 3-carbonyl quinolines is reported. The reactions proceed to afford 3-carbonyl quinoline derivatives with or without substituent at the C-4 position in good to high yields using Iron(III) chloride hexahydrate as the catalyst in the air.     

Inverse electron demand hetero-Diels–Alder reaction in preparing 1,4-benzodioxin from o-quinone and enamine

A process for synthesizing 1,4-benzodioxin, through oxidation of a phenol to an o-quinone followed by treatment with an enamine, has been developed. Adduct stereochemistry is found to be retained via this one-pot reaction. The method uses hypervalent iodine reagent under mild conditions and is compatible with a wide scope of phenols and enamines.