Significant Enhancement in the Efficiency and Selectivity of Iron‐Catalyzed Oxidative Cross‐Coupling of Phenols by Fluoroalcohols

Significant enhancement of both the rate and the chemoselectivity of iron‐catalyzed oxidative coupling of phenols can be achieved in fluorinated solvents, such as 1,1,1,3,3,3‐hexafluoropropan‐2‐ol (HFIP), 2,2,2‐trifluoroethanol (TFE), and 1‐phenyl‐2,2,2‐trifluoroethanol. The generality of this effect was examined for the cross‐coupling of phenols with arenes and polycyclic aromatic hydrocarbons (PAHs) and of phenol with β‐dicarbonyl compounds. The new conditions were utilized in the synthesis of 2′′′‐dehydroxycalodenin B in only four synthetic steps.     

Oxidative coupling polymerization of 2,3‐dihydroxynaphthalene with dinuclear‐type copper(II) catalyst

The oxidative coupling polymerization of 2,3‐dihydroxynaphthalene with the novel dinuclear‐type copper(II) catalysts successfully produced poly(2,3‐dihydroxy‐1,4‐naphthylene). For example, the MeOH‐insoluble polymer with a number average molecular weight of 4.4 × 10³ from the polymerization using the complex of CuCl₂ and N,N′‐bis(2‐morpholinoethyl)‐p‐xylylenediamine ( p ‐ 1 ) at room temperature under an O₂ atmosphere followed by acetylation of the hydroxyl groups was obtained in 63% yield. The structures of the tetraamine ligands and the counter anion of the copper(II) salts significantly influenced the catalyst activity. The polymerization of 2,2′‐dimethoxy‐1,1′‐binaphthalene‐3,3′‐diol with the 2CuCl₂‐ p ‐ 1 catalyst, however, resulted in a lower yield. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1635–1640, 2005     

Laccase‐catalyzed polymerization of lignocatechol and affinity on proteins of resulting polymers

For the synthesis of a new biologically functional polymer from a natural resource by an environment‐friendly method, the laccase‐catalyzed polymerization of a lignin‐based macromonomer, lignocatechol, was carried out for the first time in ethanol–phosphate buffer solvent system to give crosslinked polymers in good yields. Lignocatechol was prepared by the phase separation system of lignin and catechol in aqueous sulfuric acid. The copolymerization was also performed with urushiol to afford the corresponding copolymers in high yields. The polymerization mechanism was estimated by the IR and pyrolysis GC‐MS measurements, suggesting that the polymerization proceeded mainly at the catechol ring through a quinone radical intermediate. The thermal properties were measured by the DSC, TG, and TMA analyses, indicating that the polymers had high thermal stabilities because of the crosslinked structures. In addition, it was found that the resulting polymers had the affinity of bovine serum albumin (BSA) and glucoamylase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 824–832, 2009     

Direct Oxidative Coupling of N‐Acetyl Indoles and Phenols for the Synthesis of Benzofuroindolines Related to Phalarine

Inspired by the biogenetic synthesis of benzofuroindoline‐containing natural products, we designed an oxidative coupling between phenol and N‐acetyl indoles. This straightforward and direct radical process, mediated by 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone and FeCl₃ allowed the regioselective synthesis of benzofuro[3,2‐b]indolines, whose structure is found in the natural product phalarine.     

Blood‐Catalyzed RAFT Polymerization

The use of hemoglobin (Hb) contained within red blood cells to drive a controlled radical polymerization via a reversible addition‐fragmentation chain transfer (RAFT) process is reported for the first time. No pre‐treatment of the Hb or cells was required prior to their use as polymerization catalysts, indicating the potential for synthetic engineering in complex biological microenvironments without the need for ex vivo techniques. Owing to the naturally occurring prevalence of the reagents employed in the catalytic system (Hb and hydrogen peroxide), this approach may facilitate the development of new strategies for in vivo cell engineering with synthetic macromolecules.     

Laccase‐catalyzed Synthesis and Antioxidant Property of Poly(catechin)

Catechin was oxidatively polymerized by laccase in a mixture of a polar organic solvent and buffer to give a new class of flavonoid polymers. Myceliophthora laccase showed high catalytic activity for the polymerization. Using a mixed solvent of acetone and pH 5 acetate buffer efficiently produced the polymer. Under the selected conditions, DMF‐soluble polymers were obtained in good yields. Effects of reaction parameters on the yield, solubility, and molecular weight of the polymer have been systematically investigated. A radical species was detected in the polymer by ESR spectroscopy. The polymers showed greatly amplified superoxide scavenging activity and xanthine oxidase inhibitory activity compared with monomeric catechin.

Superoxide scavenging activity of poly(catechin)s, n = 3. ○: catechin, □: poly(catechin).     

Electrochemical Study of Phenolic Compounds as Enhancers in Laccase‐Catalyzed Oxidative Reactions

Sixteen phenolic compounds, twelve of which derived from lignin, were evaluated as potential mediators for laccase‐assisted bleaching of pulp. The electrochemical behavior of these phenols, alone and in the presence of the lignin model compound veratryl alcohol, was studied by means of cyclic voltammetry. All phenolic compounds showed catalytic effect on the veratryl alcohol electrochemical oxidation. However, they could not be considered as mediators, since their oxidation products are not stable and regeneration of their reduced forms was not observed. The redox potentials of the phenolic compounds seem to have a negligible effect on their catalytic efficiency, supporting a H‐abstraction oxidation mechanism. This mechanism was also confirmed by electrochemical studies of 2,4,6‐trimethylphenol in acetonitrile and in the presence of benzyl alcohols.     

Cyclodextrins in Polymer Synthesis: Enzymatic Polymerization of a 2,6‐Dimethyl‐β‐Cyclodextrin/2,4‐Dihydroxyphenyl‐4′‐Hydroxybenzylketone Host‐Guest Complex Catalyzed by Horseradish Peroxidase (HRP)

This paper reports the enzymatic polymerization of the inclusion complex 2,4‐dihydroxyphenyl‐4′‐hydroxybenzylketone/2,6‐dimethyl‐β‐cyclodextrin by horseradish peroxidase (HRP) in aqueous media. The structure of the complex was determined by means of NOESY‐NMR and crystallographic analysis (indicating an orthorhombic structure). The enzymatic polymerization of the uncomplexed 2,4‐dihydroxyphenyl‐4′‐hydroxybenzylketone yields oligomers with molecular weights up to in organic‐aqueous media, but because of its poor solubility in aqueous systems, no polymerization is observed if water is used as solvent. An increase of the availability of the ketone in solution is achieved by complexing it with random‐methylated β‐cyclodextrin in water. We found that the use of methylated β‐cyclodextrin in equimolar concentration to the monomer increases the polymerization yield and the average molecular weight. The polymers formed were analyzed by GPC and ATR‐FTIR techniques.

Representation from X‐ray diffraction analysis of the 2,6‐dimethyl‐β‐cyclodextrin/2,4‐dihydroxyphenyl‐4′‐hydroxybenzylketone host‐guest complex ( 3 ).     

Polymerization via the Ugi‐reaction using aromatic monomers

The highly modular Ugi four‐component reaction (Ugi‐4CR) was used to directly obtain polymers of high molar mass bearing aromatic residues in the backbone. By using at least two bifunctional monomers, the Ugi‐4CR can be employed to synthesize polymers through a polycondensation under mild conditions in the absence of catalysts. This highly versatile approach allows the creation of vast libraries of molecules by a comparably small pool of compounds. We investigated the six different possible types of the Ugi four‐component polymerization (Ugi‐4CP) to generate polyamides using commercially available monomers without further purification. After substantial adjustments of reaction parameters, we were able to obtain a polymer of high molar mass, albeit only for one out of the six types of the Ugi‐4CP. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1680–1686     

Enzymatic Oxidative Polymerization of Phenol in an Aqueous Solution in the Presence of a Catalytic Amount of Cyclodextrin

The peroxidase‐catalyzed polymerization of phenol in aqueous solution has been examined in the presence of 2,6‐di‐O‐methyl‐α‐cyclodextrin (DM‐α‐CD). By the addition of DM‐α‐CD, the phenol was polymerized in a buffer to produce the soluble polyphenol. Only a catalytic amount of DM‐α‐CD induced the polymerization effectively. A small amount of DM‐α‐CD was contained in the polymer.     

Oxidative Polymerization of Silylthioketene Dimer

Summary: The first π‐conjugated poly(thioketene dimer) was synthesized via the homopolymerization of a silylthioketene dimer by a chemical oxidation‐reduction process. The polymerization of trimethylsilylthioketene dimer in the presence of FeCl₃ (in CHCl₃ at 70 °C for 24 h) gave the corresponding doped poly(thioketene dimer). After treatment of the doped polymer with an aqueous solution of ammonia, the neutral poly(thioketene dimer) was obtained with an incidental desilylation. The polymer obtained was soluble in DMF and DMSO. From gel permeation chromatographic analysis (DMF, polystyrene standards), the number‐average molecular weight of the polymer was found to be 7 460. The polymer showed low oxidation potentials derived from the thioketene dimer unit. An effective extension of the π‐conjugation was observed in the polymer.

Synthesis of π‐conjugated poly(thioketene dimer).     

New Polymers from Natural Phenols Using Horseradish or Soybean Peroxidase

The flavonol quercetin, its glycoside rutin, the flavanol catechin, the isoflavone daidzein and 5,6,4′‐trihydroxyisoflavone can be oxidatively polymerized via a radical polyrecombination mechanism catalyzed by horseradish or soybean peroxidase in a mixture of phosphate buffer (pH 7) and 1,4‐dioxane. The average molecular weights of the polymers were found to be in the range 4 000–12 000 g/mol. Daidzein derivatives with a methoxy (formononetin) or nitro group or a hydrogen atom at C‐4′ could not be polymerized under these conditions. These results and molecular modeling studies suggest that polymerization preferentially occurs via the electron‐rich ring B of the isoflavonoids. The polymers were characterized by means of FT‐IR and UV spectroscopy, and their redox behavior was analyzed using cyclic voltammetry.     

Polymerization of Tellurophene Derivatives by Microwave‐Assisted Palladium‐Catalyzed ipso‐Arylative Polymerization

We report the synthesis of a tellurophene‐containing low‐bandgap polymer, PDPPTe2T, by microwave‐assisted palladium‐catalyzed ipso‐arylative polymerization of 2,5‐bis[(α‐hydroxy‐α,α‐diphenyl)methyl]tellurophene with a diketopyrrolopyrrole (DPP) monomer. Compared with the corresponding thiophene analog, PDPPTe2T absorbs light of longer wavelengths and has a smaller bandgap. Bulk heterojunction solar cells prepared from PDPPTe2T and PC₇₁BM show PCE values of up to 4.4 %. External quantum efficiency measurements show that PDPPTe2T produces photocurrent at wavelengths up to 1 µm. DFT calculations suggest that the atomic substitution from sulfur to tellurium increases electronic coupling to decrease the length of the carbon–carbon bonds between the tellurophene and thiophene rings, which results in the red‐shift in absorption upon substitution of tellurium for sulfur.