Oxidative Dimerization Reaction Research Articles

Porous Organic Polymers (POPs) Based on Acridone as Heterogeneous Photocatalysts for Oxidative Dimerization and Cyclocondensation Reactions

AbstractPorous organic polymers (POPs) are emergent tailor‐made materials, which can be accessed by covalent polymerization of diligently designed molecular building blocks in a bottom‐up fashion. Acridone, a well‐known chromophore that undergoes intersystem crossing (ISC) with near‐unity quantum yield akin to benzophenone, was structurally elaborated into a building block and subjected to Friedel‐Crafts polyalkylation to afford a series of POPs, namely, Ac‐MePOP, Ac‐OMePOP, and Ac‐CBPOP. These POPs exhibit remarkable porosity and significant absorption in the visible region. Of the three polymers, Ac‐CBPOP with the highest BET surface area of ca. 1027 m2/g is shown to serve as an excellent heterogeneous photocatalyst for visible light‐mediated oxidative transformations, that is, oxidative coupling of benzylamines to imines and cyclocondensation of o‐phenylenediamines with aldehydes to benzimidazoles under oxygen atmosphere. It is further shown that Ac‐CBPOP can be reused for several reaction cycles without any loss of catalytic activity with its stability intact. Mechanistic studies show that 1O2 serves as the key reactive oxygen species, formed by the energy transfer from Ac‐CBPOP to 3O2, in the photocatalytic oxidation reactions. The results demonstrate the development of stable photocatalytic POP materials with tailor‐made properties by a bottom‐up covalent polymerization of programmed molecular building blocks.

Highly chemoselective oxidative dimerization of indolosesquiterpene alkaloids: a biomimetic approach to dixiamycin.

Dimeric indolosesquiterpene alkaloids, typically N-N- and C-N-linked xiamycin dimers, feature a pentacyclic framework with four contiguous stereogenic centers at the periphery of a trans-decalin scaffold to which a carbazole unit is attached. In comparison with actual biosynthetic dixiamycin derivatives, we designed C-C-linked xiamycin dimers, aiming to use them as a powerful tool to create unique scaffolds as drug candidates. In this work, we disclose the first synthetic route to access a C-C dimeric indolosesquiterpene skeleton, featuring a hypervalent iodine (PIFA)-catalyzed oxidative dimerization reaction in a single-step operation with overwhelming control over the chemoselectivity and regioselectivity. This strategy has been successfully applied to the synthesis of a C-C dimer of xiamycin A (3) and xiamycin A methyl ester (15) that demonstrates a new synthetic pathway for dimeric indolosesquiterpene alkaloids.

The Effects of Structure and Oxidative Polymerization on Antioxidant Activity of Catechins and Polymers.

Polyphenols are key free radical scavengers in tea. This study screened the antioxidant active groups of catechins and dimers and analyzed the effects of the degree of oxidative polymerization and oxidative dimerization reaction on their antioxidant activities. ABTS+· free radical scavenging activity, DPPH free radical scavenging activity, and total antioxidant capacity of catechins and polymers were systematically analyzed and compared in this study. Results manifested antioxidant activities of catechins were dominated by B-ring pyrogallol and 3-galloyl, but were not decided by geometrical isomerism. 3-galloyl had a stronger antioxidant activity than B-ring pyrogallol in catechins. The number, not the position, of the galloyl group was positively correlated with the antioxidant activities of theaflavins. Theasinensin A has more active groups than (-)-epigallocatechin gallate and theaflavin-3,3'-digallate, so it had a stronger antioxidant activity. Additionally, the higher the degree of oxidation polymerization, the weaker the antioxidant activities of the samples. The oxidative dimerization reaction hindered the antioxidant activities of the substrate-catechin mixture by reducing the number of active groups of the substrate and increasing the molecular structure size of the product. Overall, pyrogallol and galloyl groups were antioxidant active groups. The degree of oxidative polymerization and the oxidative dimerization reaction weakened the antioxidant activity.

Total Synthesis of (-)-Calycanthine via Iron-Catalyzed Stereoselective Oxidative Dimerization.

Dimeric cyclotryptamine alkaloids typically feature vicinal all-carbon quaternary stereocenters and four nitrogen atoms. In comparison with the actual biosynthetic tryptophan derivatives, we designed the 2N-featured monomer 7, aiming to construct vicinal all-carbon quaternary stereocenters via a one-step dimerization process to access the 4N-featured isomeric members of this family. In this work, we disclose the first synthetic route to access the skeleton of (-)-isocalycanthine, featuring an iron-catalyzed oxidative dimerization reaction in a catalytic single-step operation with an overwhelming control of the absolute and relative stereochemistry. This strategy has been successfully applied to the total synthesis of (-)-calycanthine and 16 isocalycanthine derivatives, which demonstrates a new synthetic pathway for dimeric cyclotryptamine alkaloids.

Deuterated Indocyanine Green (ICG) with Extended Aqueous Storage Shelf-Life: Chemical and Clinical Implications.

Indocyanine Green (ICG) is a clinically approved near‐infrared fluorescent dye that is used extensively for various imaging and diagnostic procedures. One drawback with ICG is its instability in water, which means that reconstituted clinical doses have to be used very shortly after preparation. Two deuterated versions of ICG were prepared with deuterium atoms on the heptamethine chain, and the spectral, physiochemical, and photostability properties were quantified. A notable mechanistic finding is that self‐aggregation of ICG in water strongly favors dye degradation by a photochemical oxidative dimerization reaction that gives a nonfluorescent product. Storage stability studies showed that replacement of C−H with C−D decreased the dimerization rate constant by a factor of 3.1, and it is likely that many medical and preclinical procedures will benefit from the longer shelf‐lives of these two deuterated ICG dyes. The discovery that ICG self‐aggregation promotes photoinduced electron transfer can be exploited as a new paradigm for next‐generation photodynamic therapies.

Formal Aerobic Oxidative Cross-Coupling of Benzofuranones with Azo Compounds Using Pd-μ-hydroxo Complex.

We have developed a catalytic aerobic oxidative dimerization reaction of benzofuranones using a Pd(II)-µ-hydroxo complex. Radical-radical cross-coupling of the resulting dimers with azo compounds enabled the one-pot synthesis of structurally congested benzofuranones having two distinct vicinal all-carbon quaternary centers.

Enzyme-mediated oxidative dimerization reactions of cyano-resveratrol analogues

The synthesis and oxidative coupling reactions of two cyano-resveratrol analogues were studied. An 8-5-coupled dihydrobenzofuran-type dimer and an 8-8-coupled diastereoisomeric indane mixture were prepared. The cyano groups of the resveratrol analogues had almost no influence on the regio- or stereoselectivity of the coupling reactions of the two precursors.

Straightforward and Expeditious One-Pot Tandem Synthesis of 3,5-Diaryl-1,2,4-Selenadiazoles from Aryl Nitriles

A one-pot process for the efficient synthesis of 3,5-diaryl-1,2,4-selenadiazoles from aryl nitriles has been developed. This tandem transformation was performed in excellent yields (91–98%) via in situ selenoamidation and a subsequent oxidative dimerization reaction. This method features relatively mild reaction conditions, operational simplicity, straightforward separation of the products, and the utilization of inexpensive reagents.

Nitrogen-Bridged Metallodiazaporphyrin Dimers: Synergistic Effects of Nitrogen Bridges and meso-Nitrogen Atoms on Structure and Properties.

NH-bridged and pyrazine-fused metallodiazaporphyrin dimers have been prepared from nickel(II) and copper(II) complexes of 3-amino-5,15-diazaporphyrin by Pd-catalyzed C-N cross-coupling and oxidative dimerization reactions, respectively. The synergistic effects of the nitrogen bridges and meso-nitrogen atoms play major roles in enhancing the light-harvesting properties and delocalization of an electron spin over the entire π-skeletons of the metallodiazaporphyrin dimers.

Rigid Conjugated Twisted Truxene Dimers and Trimers as Electron Acceptors

AbstractA new class of rigid twisted truxenone oligomers with an enlarged π backbone has been established by oxidative dimerization reactions. The resulting extended conjugated systems have large extinction coefficients and low‐lying LUMO levels and show good solubility in common organic solvents, thus making them attractive compounds as new electron acceptors in organic electronics. Their suitability as electron acceptors has been demonstrated in bulk‐heterojunction organic solar cells with poly({4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl}{3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl}) (PTB7) as the donor material.

Rigid Conjugated Twisted Truxene Dimers and Trimers as Electron Acceptors.

A new class of rigid twisted truxenone oligomers with an enlarged π backbone has been established by oxidative dimerization reactions. The resulting extended conjugated systems have large extinction coefficients and low-lying LUMO levels and show good solubility in common organic solvents, thus making them attractive compounds as new electron acceptors in organic electronics. Their suitability as electron acceptors has been demonstrated in bulk-heterojunction organic solar cells with poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) as the donor material.

Distribution of manganese species in an oxidative dimerization reaction of a bis-terpyridine mononuclear manganese (II) complex and their heterogeneous water oxidation activities

Heterogeneous water oxidation catalyses were studied as a synthetic model of oxygen evolving complex (OEC) in photosynthesis using mica adsorbing various manganese species. Distribution of manganese species formed in the oxidative dimerization reaction of [MnII(terpy)2]2+ (terpy=2,2′:6′,2″-terpyridine) (1′) with various oxidants in water was revealed. 1′ was stoichiometrically oxidized to form di-μ-oxo dinuclear manganese complex, [(OH2)(terpy)MnIII(μ-O)2MnIV(terpy)(OH2)]3+ (1) by KMnO4 as an oxidant. When Oxone and Ce(IV) oxidants were used, the further oxidation of 1 to [(OH2)(terpy)MnIV(μ-O)2MnIV(terpy)(OH2)]4+ (2) was observed after the oxidative dimerization reaction of 1′. The mica adsorbates with various composition of 1′, 1 and 2 were prepared by adding mica suspension to the various oxidant-treated solutions followed by filtration. The heterogeneous water oxidation catalysis by the mica adsorbates was examined using a Ce(IV) oxidant. The observed catalytic activity of the mica adsorbates corresponded to a content of 1 (1ads) adsorbed on mica for KMnO4- and Oxone-treated systems, indicating that 1′ (1′ads) and 2 (2ads) adsorbed on mica do not work for the catalysis. The kinetic analysis suggested that 1ads works for the catalysis through cooperation with adjacent 1ads or 2ads, meaning that 2ads assists the cooperative catalysis by 1ads though 2ads is not able to work for the catalysis alone. For the Ce(IV)-treated system, O2 evolution was hardly observed although the sufficient amount of 1ads was contained in the mica adsorbates. This was explained by the impeded penetration of Ce(IV) ions (as an oxidant for water oxidation) into mica by Ce3+ cations (generated in oxidative dimerization of 1′) co-adsorbed with 1ads.

Copper catalyzed sequential arylation−oxidative dimerization of o-haloanilides: synthesis of dimeric HPI alkaloids

In this communication, we report a copper catalyzed sequential arylation-oxidative dimerization reaction as the key step for the synthesis of hexahydropyrroloindole alkaloids (+)-chimonanthine, (+)-folicanthine and (-)-calycanthine.

Bromophenyl substituted dithiafulvenes and tetrathiafulvalene vinylogues: synthesis, structure, and electronic properties

Abstract Bis(bromophenyl) substituted tetrathiafulvalene vinylogues (TTFVs) were prepared via oxidative dimerization reactions of corresponding bromophenyl substituted dithiafulvene precursors. The synthesis of ortho-bromophenyl TTFVs led to the formation of an unexpected bis-spiro product, the structure of which was clearly elucidated by single crystal X-ray crystallography. Electronic and redox properties of the bromophenyl substituted dithiafulvenes, TTFV derivatives, and the related bis-spiro compound were investigated by UV–vis spectroscopic and cyclic voltammetric analyses. Detailed structure–property relationships have been discussed.

Oxidative Dimerization of Aromatic Amines using tBuOI: Entry to Unsymmetric Aromatic Azo Compounds

It's all the hype: An oxidative dimerization reaction of aromatic amines utilizing tert-butyl hypoiodite (tBuOI) under mild reaction conditions leads to aromatic azo compounds. The method allows access to unsymmetric aromatic azo compounds, which are difficult to prepare by conventional synthetic methods, in a selective manner.

ChemInform Abstract: Gold Nanoparticles Supported on TiO2 Catalyze the Cycloisomerization/Oxidative Dimerization of Aryl Propargyl Ethers.

AbstractThe gold‐catalyzed cycloisomerization of propargyl ethers (I) is accompanied by an oxidative dimerization reaction to afford mixtures of chromenes (II) and dimeric by‐products (III).

Different reaction modes for the oxidative dimerization of epoxyquinols and epoxyquinones. Importance of intermolecular hydrogen-bonding.

An oxidative dimerization reaction, involving the three successive steps of oxidation, 6 pi-electrocyclization, and Diels-Alder reaction, has been experimentally and theoretically investigated for the three 2-alkenyl-3-hydroxymethyl-2-cyclohexen-1-one derivatives epoxyquinol 3, epoxyquinone 6, and cyclohexenone 10. Of the sixteen possible modes of the oxidation/6 pi-electrocylization/Diels-Alder reaction cascade for the epoxyquinone 6, and eight for the cyclohexenone 10, only the endo-anti(epoxide)-anti(Me)-hetero and endo-anti(Me)-hetero modes are, respectively, observed, while both endo-anti(epoxide)-anti(Me)-hetero and exo-anti(epoxide)-anti(Me)-homo reaction modes occur with the epoxyquinol 3. Intermolecular hydrogen-bonding is found to be the key cause of formation of both epoxyquinols A and B with 3, although epoxyquinone 6 and cyclohexenone 10 both gave selectively only the epoxyquinol A-type product. In the dimerization of epoxyquinol 3, two monomer 2H-pyrans 5 interact with each other to afford intermediate complex 28 or 29 stabilized by hydrogen-bonding, from which Diels-Alder reaction proceeds. Theoretical calculations have also revealed the differences in the reaction profiles of epoxyquinone 6 and cyclohexenone 10. Namely, the rate-determining step of the former is the Diels-Alder reaction, while that of the latter is the 6 pi-electrocyclization.

The versatile chemistry of the [B20H18]2- ions: novel reactions and structural motifs.

Among the polyhedral [closo-BnHn]2- ion series (n = 5-12 inclusive) the aromatic [closo-B10H10]2- ion is both readily available and quite reactive. Among its many reactions which retain its cage structure one finds the oxidative dimerization reaction in which two [closo-B10H12]2- ions each formally lose a hydride ion and undergo dimerization of the resulting [closo-B10H9]- ions to produce the [trans-B20H18]2- ion. The two-component [closo-B10H9]- ions of the latter are linked together by a pair of unique B-B-B bonds which provide unprecedented reactivity to the structure. Among these reactions are the two-electron reduction to a set of three interconvertible [B20H18]4- ions having intercage B-B bonds and the related reductive substitution reaction in which [trans-B20H18]2- undergoes attack by nucleophile, L, to produce [B20H18L]2-. The latter species is formally a substituted [B20H19]3- (L = H) ion formed by B-B bond protonation of one of the isomeric [B20H18]4- ions. These and a variety of novel reactions are described here along with interrelated reaction mechanisms considered for the first time.

Novel TTF vinylogues affording stable cation radicals

Novel TTF vinylogues with extended π-conjugation have been synthesized using an oxidative dimerization reaction of 1, 4-dithiafulvenes. The cation radicals of the derivatives with o-substituted phenyl groups are thermodynamically stable where the aryl units are twisted and the TTF vinylogue skeleton is planar. Some compounds afforded cation radical salts upon electrochemical oxidation. X-ray structure analyses revealed unusual crystal structures.

Osmium-Promoted Oxidative Dimerization of Aminoarenes to N-Aryl-o-arenoquinone Diimines (L). Synthesis, Structure, Electrochemistry, and Reactivity of OsBr(2)L(2).

A family of o-arenoquinone diimine chelates, OsBr(2)L(2) (1, L = N-aryl-o-arenoquinone diimine), were isolated from the reaction of (NH(4))(2)OsBr(6) and primary aromatic amines, Ar-NH(2). These complexes constitute the first examples of osmium compounds of the o-benzoquinone diimine family. The above oxidative dimerization reaction of Ar-NH(2) was authenticated by the X-ray structure determination of a representative example. The X-ray structure of OsBr(2)L(2) (R = H) revealed a cis geometry with respect to two coordinated bromides. The bond length trends within the chelate as well as the aromatic rings are consistent with a diimine character of the ligand bound to osmium in its bivalent oxidation state. The complexes showed multiple transitions in near-IR and visible regions. These are electroactive and undergo multiple electron transfer. Three successive voltammetric responses, two oxidative and one reductive, were observed. The potential range was +1.7 to -0.8 V vs SCE in CH(3)CN solution (Pt electrode). The potentials of the above responses for differently substituted compounds depend on the Hammett summation operatorsigma(p) parameters of the substitution on L. The EPR spectrum of the electrogenerated 1-electron-oxidized complex 1a(+) is described. The electrode potentials of 1 are compared with those of related systems. A qualitative correlation between Os-N bond distances and Os(III)/Os(II) formal potentials for the Os(II) compounds of three different N,N donors is noted. The synthesis of a mixed-ligand tris chelate, [Os(bpy)L(2)](ClO(4))(2).H(2)O, is described, involving the reaction of 1 equiv of 1 with 2 equiv of Ag(bpy)(2)(+). The redox properties of the tris complex are reported. Crystal data for OsBr(2)L(2) (R = H) are as follows: empirical formula C(24)H(20)Br(2)N(4)Os; crystal system triclinic, space group P&onemacr;; a = 10.464(6) Å, b = 11.778(6) Å, c = 12.595(10) Å; alpha = 103.86(5) degrees, beta = 112.72(6) degrees, gamma = 107.79(4) degrees; V = 1245.3(10) Å(3); Z = 2; R = 4.46%; R(w) = 5.21%.