Dewen Dong

The development of copper-catalyzed aerobic oxidative coupling of H-tetrazoles with boronic acids and an insight into the reaction mechanism.

The development of a highly efficient and practical protocol for the direct C-N coupling of H-tetrazole and boronic acid was presented. A careful and patient optimization of a variety of reaction parameters revealed that this conventionally challenge reaction could indeed proceed efficiently in a very simple system, that is, just by stirring the tetrazoles and boronic acids under oxygen in the presence of different Cu(I) or Cu(II) salts with only 5 mol % loading in DMSO at 100 °C. Most significantly, the reaction could proceed very smoothly in a regiospecific manner to afford the 2,5-disubstituted tetrazoles in high to excellent yields. A mechanistic study revealed that both tetrazole and DMSO are crucial for the generation of catalytically active copper species in the reaction process in addition to their role as reactant and solvent, respectively. It is demonstrated that in the reaction cycle, the Cu(I) catalyst could be oxidized to Cu(II) by oxygen to form a [CuT2D] complex (T = tetrazole anion; D = DMSO) through an oxidative copper amination reaction. The Cu(II) complex thus formed was confirmed to be the real catalytically active copper species. Namely, the Cu(II) complex disproportionates to aryl Cu(III) and Cu(I) in the presence of boronic acid. Facile elimination of the Cu(III) species delivers the C-N-coupled product. The results presented herein not only provide a reliable and efficient protocol for the synthesis of 2,5-disubstituted tetrazoles, but most importantly, the mechanistic results would have broad implications for the de novo design and development of new methods for Cu-catalyzed coupling reactions.

Synthesis and characterization of thermotropic liquid crystalline poly(ester imide)s

Two closely series of poly(ester imide)s had been synthesized by solution polycondensation of p-phenylenebis(trimellitate) dianhydride with aliphatic diamines. The differential scanning calorimetry (DSC) traces of the most poly(ester imide)s exhibited two endotherms representing the solid state to anisotropic phase transition (T-m1) and the anisotropic to isotropic melt transition (T-m2), respectively. Observation under polarizing microscope and wide-angle X-ray diffraction (WAXD) measurements suggested that the anisotropic phase formed above the melting paints (T-m1) had a smectic character. The thermogravimetric analyses (TGA) revealed that the thermal stabilities of the poly(ester imide)s were up to 350 degrees C

Indocyanine green-functionalized bottle brushes of poly(2-oxazoline) on cellulose nanocrystals for photothermal cancer therapy

Deriving from the most abundant and renewable material, cellulose nanocrystals (CNCs) have drawn increasing attention in nanomedicine as well as other biomedical fields due to their excellent physicochemical properties and unique rod-like geometry. In this work, we report an efficient procedure to create biocompatible poly(2-oxazoline)s with a defined bottle brush architecture on CNCs through UV-induced photopolymerization and subsequent living cationic ring-opening polymerization. Characterization of the poly(2-oxazoline) modified CNCs indicates an improved thermal stability with the crystalline structure as well as the rod-like contour intact. The side chain terminal piperidinium of the bottle brush was utilized to immobilize indocyanine green (ICG) via electrostatic interactions. The resulting nanorods exhibit low toxicity in the dark and an efficient photothermal therapeutic effect against HeLa cells under 808 nm near infrared laser irradiation after being internalized by cancer cells. Moreover, bottle brushes on CNCs with amphiphilic poly(2-n-propyl-2-oxazoline) side chains show a higher efficiency in stabilizing ICG in comparison to those with hydrophilic poly(2-methyl-2-oxazoline) side chains, thus a higher photostability and a greater therapeutic effect were revealed for amphiphilic polymer modified CNCs. This work indicates that poly(2-oxazoline) functionalized CNCs represent a novel and promising platform for the design of other CNC-based drug delivery systems.

Polymer brushes on metal–organic frameworks by UV-induced photopolymerization

Metal–organic frameworks (MOFs) are extremely promising candidates for application in diverse fields. However, a limitation to the widespread use of MOFs is the absence of a facile and efficient chemical modification method which can greatly improve their poor processability and stability without altering the inherent outstanding chemical and physical properties. Herein, we report a universal post-synthetic modification strategy by directly forming polymer brushes on MOF surfaces without any premodification or immobilization of initiators via UV-induced photopolymerization. The method is applicable to a series of representative MOFs, allowing the formation of polymer brushes on the exterior surface of nanoMOFs and MOF membranes. Characterization of the polymer brushes indicates a high grafting density of grafted polymer chains, thus endowing MOFs with improved thermal/chemical stabilities with the inner chemical structure and porosity intact. Moreover, the polymer modification facilitates an efficient removal of organic dyes from water solutions.

Direct functionalization of cellulose nanocrystals with polymer brushes via UV-induced polymerization: access to novel heterogeneous visible-light photocatalysts

Cellulose nanocrystals (CNCs) are an exciting class of bio-based materials attracting increasing interest for a wide range of potential applications due to their nanoscale dimensions, biocompatibility, biodegradability and large surface area. In this work, we report a universal and facile strategy for the preparation of polymer brushes on CNCs via photopolymerization in the absence of any initiator immobilization. The reported procedure is applicable to a series of vinyl monomers, leading to the direct creation of homogeneous and stable polymer coatings on CNCs. Characterization of the resulting polymer-grafted CNCs by FTIR spectroscopy, XRD, AFM and TGA indicates a high grafting density, enhanced dispersing ability and thermal stability without altering the crystalline structure of the intrinsic CNCs. Finally, we have demonstrated the possibility to covalently attach 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene to the grafted polymer chain ends through polymer analogous reactions. The afforded nano-objects show visible-light photocatalytic activity and chemoselectivity in the oxidization reaction of thioanisole to methyl phenyl sulfoxide.

POCl3-Mediated Reaction of 1-Acyl-1-carbamoyl Oximes: A New Entry to Cyanoformamides

A facile and efficient one-pot synthesis of cyanoformamides was developed from readily available 1-acyl-1-carbamoyl oximes mediated by phosphoryltrichloride (POCl3) under mild conditions in good to high yields.

Phenyliodine(III) Diacetate Mediated Oxidative Cyclization of 1-Alkenoyl-1-carbamoyl Cycloalkanes: Access to Spiro-Fused Dihydrofuran-3(2H)-ones

Facile and efficient synthesis of spiro-fused dihydrofuran-3(2H)-ones was developed via phenyliodine(III) diacetate (PIDA) mediated oxidative cyclization of 1-alkenoyl-1-carbamoyl cycloalkanes under very mild conditions.

Ultrathin free-standing polymer membranes with chemically responsive luminescence via consecutive photopolymerizations

A facile and general method for the preparation of chemically responsive polymer films is demonstrated. First, a crosslinked polymer precoating layer is created via self-initiated photografting and photopolymerization of ethylene glycol dimethacrylate on a self-assembled monolayer of a 3-(trimethoxysilyl)propylamine modified oxidized silicon wafer. The intact methacrylate functionalities are used to grow polymer chains by a second self-initiated photografting and photopolymerization of vinyl monomers to form polymer brushes on the crosslinked layer; thus a series of polymer membranes of PMMA, PDMAEMA and P4VP are obtained. The double-layered polymer membranes can be lifted off via hydrofluoric acid etching of the oxidized silicon layer to give integral free-standing polymer membranes. Kinetic studies revealed that the thickness of both the crosslinked precoating layer and the brush layer increased linearly as a function of the polymerization time before the reaction solutions got highly viscous. Furthermore, polyoxometalate Na9(EuW10O36) can be uniformly incorporated into the PDMAEMA membrane through electrostatic interactions to afford an acid/base gas-responsive luminescent hybrid film.

PBr3-mediated [5 + 1] annulation of α-alkenoyl-α-carbamoyl ketene-S,S-acetals: access to substituted pyridine-2,6(1H,3H)-diones

A facile and efficient synthesis of substituted pyridine-2,6(1H,3H)-diones via an intramolecular [5 + 1] annulation of readily available α-alkenoyl-α-carbamoyl ketene-S,S-acetals mediated by phosphorus bromide (PBr3) under very mild conditions is described.