Electron-rich Phosphines Catalyzed Head-to-Tail Dimerization of Renewable Alkyl Crotonates.

Herein, a facile head-to-tail dimerization of alkyl crotonates using electron-rich N,N'-bis(imidazolyl) guanidinylphosphines (BIG-Ps) as organocatalysts was firstly developed. This reaction proceeded smoothly under mild reaction conditions, effectively generating a series of functionalized 2-ethylidene-3-methylpentanedioates in excellent yields and stereoselectivity. Furthermore, this method was successfully applied for the synthesis of unsaturated polyesters by employing alkyl dicotonates as monomers.

Electrochemical ring-opening carboxylation of cyclic carbonate with carbon dioxide.

Electroreductive ring-opening carboxylation of styrene carbonates with CO to achieve dicarboxylic acids and/or -hydroxy acids has been developed the selective cleavage of the C(sp)-O bond in cyclic carbonates. The product selectivity is probably determined by the stability and reactivity of the key benzylic radical and carbanion intermediate.

Innovative Approach to Chiral Polyurethanes: Asymmetric Copolymerization with Isocyanates.

The introduction of nitrogen-containing functional groups to chiral polymer backbones enables the tailoring of physical properties and offers opportunities for further post-polymerization modification. However, the substrate scope of such polymers is extremely limited because monomers having nitrogen-containing groups can change coordination state with respect to the metal centers, thus decreasing the activity and enantioselectivity and even poisoning the catalyst completely. In this paper, we report our attempts to carry out the asymmetric copolymerization of meso-epoxide with highly reactive isocyanates.

Stereoregular poly(2-phenylthiirane) cationic ring-opening polymerization.

Herein, we describe an effective strategy for synthesizing polythioethers with a well-defined structure through the cationic polymerization of thiirane with electron-withdrawing substituents. This strategy allows for precisely controlling the regio- and stereochemistry of the ring-opening polymerization of 2-phenylthiirane, thus allowing for producing poly(2-phenylthiirane) with high stereoregularity using enantiomeric pure thiirane.

Closed-loop recycling of sulfur-rich polymers with tunable properties spanning thermoplastics, elastomers, and vitrimers.

The development of closed-loop recycling polymers that exhibit excellent performance is of great significance. Sulfur-rich polymers possessing excellent optical, thermal, and mechanical properties are promising candidates for chemical recycling but lack efficient synthetic strategies for achieving diverse structures. Herein, we report a universal synthetic strategy for producing polytrithiocarbonates, a class of sulfur-rich polymers, via the polycondensation of dithiols and dimethyl trithiocarbonate.

A Powerful Strategy for Synthesizing Block Copolymers via Bimetallic Synergistic Catalysis.

Block copolymers, comprising polyether and polyolefin segments, are an important and promising category of functional materials. However, the lack of efficient strategies for the construction of polyether-b-polyolefin block copolymers have hindered the development of these materials. Herein, we propose a simple and efficient method to obtain various block copolymers through the copolymerization of epoxides and acrylates via bimetallic synergistic catalysis.

Electroreductive Ring-Opening Carboxylation of 1,3-Oxazolidin-2-ones with CO for Accessing β-Amino Acids.

Electrocarboxylation of the C(sp)-O bond in 1,3-oxazolidin-2-ones with CO to achieve β-amino acids is developed. The C-O bond in substrates can be selectively cleaved via the single electron transfer on the surface of a cathode or through a CO  intermediate under additive-free conditions. A great diversity of β-amino acids can be obtained in a moderate to excellent yield and readily converted to various biologically active compounds.

Copolymerization Involving Sulfur-Containing Monomers.

Incorporating sulfur (S) atoms into polymer main chains endows these materials with many attractive features, including a high refractive index, mechanical properties, electrochemical properties, and adhesive ability to heavy metal ions. The copolymerization involving S-containing monomers constitutes a facile method for effectively constructing S-containing polymers with diverse structures, readily tunable sequences, and topological structures. In this review, we describe the recent advances in the synthesis of S-containing polymers via copolymerization or multicomponent polymerization techniques concerning a variety of S-containing monomers, such as dithiols, carbon disulfide, carbonyl sulfide, cyclic thioanhydrides, episulfides and elemental sulfur (S).

Eletrocarboxylation Reactions Using CO Both as Promoter and Carboxylative Reagent.

Electrocarboxylation reaction, which employs organic electrosynthesis to achieve the utilization of CO as a carboxylative reagent, provides a powerful and efficient tool for the preparation of organic carboxylic acid. In some electrocarboxylation reactions, CO also acts as a promoter to facilitate the desired reaction. This concept mainly highlights recent CO -promoted electrocarboxylation reactions via CO intermediate or transiently protective carboxylation of active intermediate with CO .

Cationic ring-opening polymerization of -benzylaziridines to polyamines organic boron.

This communication reports the synthesis of cyclic polyamines the cationic ring-opening polymerization (CROP) of -benzylaziridines initiated by tris(pentafluorophenyl)borane. The debenzylation of these polyamines afforded water-soluble polyethylenimine derivatives. The electrospray ionization mass spectrometry and density functional theory results revealed that the CROP proceeded the activated chain end intermediates.

Direct and Selective Electrocarboxylation of Styrene Oxides with CO for Accessing β-Hydroxy Acids.

Highly selective and direct electroreductive ring-opening carboxylation of epoxides with CO in an undivided cell is reported. This reaction shows broad substrate scopes within styrene oxides under mild conditions, providing practical and scalable access to important synthetic intermediate β-hydroxy acids. Mechanistic studies show that CO functions not only as a carboxylative reagent in this reaction but also as a promoter to enable efficient and chemoselective transformation of epoxides under additive-free electrochemical conditions.

A sustainable approach for the synthesis of recyclable cyclic CO-based polycarbonates.

It is highly desirable to reduce the environmental pollution related to the disposal of end-of-life plastics. Polycarbonates derived from the copolymerization of CO and epoxides have attracted much attention since they can enable CO-fixation and furnish biorenewable and degradable polymeric materials. So far, only linear CO-based polycarbonates have been reported and typically degraded to cyclic carbonates.

Electrocarboxylation of -Acylimines with Carbon Dioxide: Access to Substituted α-Amino Acids.

Direct electrocarboxylation of various -acylimines with atmospheric CO is achieved in an undivided cell under mild conditions, affording substituted α-amino acids in yields of 62-95%. This reaction is conducted with high efficiency using triethanolamine as an external reductant under nonsacrificial anode conditions, and can be facilely performed on gram scale. Preliminary mechanistic studies including cyclic voltammetry and control experiments support -radical carbanion as the key intermediate.

Controlled Disassembly of Elemental Sulfur: An Approach to the Precise Synthesis of Polydisulfides.

The usage of elemental sulfur (S ) for constructing sulfur-containing polymers is of great significance in terms of sulfur resource utilization or fabrication of high-performance polymers. Currently, the random disassembly of S hinders its direct use in the precise synthesis of sulfur-containing polymers. Herein, we provide an effective strategy for controlling the dismantlement of S to synthesize polydisulfides, a promising category of dynamic bonds containing polymers.

COS-triggered oxygen/sulfur exchange of isatins: chemoselective synthesis of functionalized isoindigos and spirothiopyrans self-condensation and the thio-Diels-Alder reaction.

Herein, we present the first organocatalytic oxygen/sulfur atom exchange reaction (O/S ER) of isatins by employing carbonyl sulfide (COS) as a novel sulfuring reagent under mild reaction conditions. 8-Diazabicyclo[5.4.

Photoinduced Reversible Semicrystalline-to-Amorphous State Transitions of Stereoregular Azopolyesters.

We report the synthesis of isotactic azobenzene-based polyesters (azopolyesters) with main-chain chirality via highly enantioselective resolution copolymerization of racemic azobenzene-containing epoxides with cyclic anhydrides. All polyesters with trans-azobenzene moieties were found to be semicrystalline materials with melting temperatures of 153-231 °C, while the corresponding isotactic cis-azopolyesters were amorphous. The azobenzene groups in the copolymers exhibited reversible trans-to-cis and cis-to-trans photoisomerization upon irradiation with light.

Randomly Distributed Sulfur Atoms in the Main Chains of CO -Based Polycarbonates: Enhanced Optical Properties.

Polymeric materials possessing both high refractive indices and high Abbe numbers are much in demand for the development of advanced optical devices. However, the synthesis of such functional materials is a challenge because of the trade-off between these two properties. Herein, a synthetic strategy is presented for enhancing the optical properties of CO -based polycarbonates by modifying the polymer's topological structure.

Carboxylative Cyclization of 2-Butenoates with Carbon Dioxide: Access to Glutaconic Anhydrides.

Cyclic anhydrides are versatile synthons and functional comonomers. Herein, we reported an organic base-promoted carboxylative cyclization of 2-butenoates with carbon dioxide to produce important glutaconic anhydrides in good yields. This metal-free reaction showed broad substrate scopes and proceeded under mild reaction conditions.

Evaluation of the Lewis acidity of metal complexes using ESI mass spectrometry.

Metal complexes have extensive applications in catalysis, however, the efficient evaluation of Lewis acidity of metal complexes is still a challenge. Herein, we report a method by using electrospray ionization mass spectrometry (ESI-MS) to evaluate the Lewis acidity of metal complexes in the presence of a reference Lewis base, in which the value of the Lewis acidity can be quantized by the bond dissociation energy (BDE) of the resultant Lewis acid-base pairs. Using this method, the Lewis acidity of tetradentate Schiff-base metal complexes (designated as salenMX), a class of common metal complexes in the homogeneous catalysis, was studied in detail.

Enantioselective terpolymerization of racemic and -epoxides with anhydrides for preparation of chiral polyesters.

The preparation of stereochemistry- and sequence-defined polymers, in which different monomer units are arranged in an ordered fashion just like biopolymers, is of great interest and has been a long-standing goal for chemists due to the expectation of unique macroscopic properties. Here, we describe the enantioselective terpolymerization of racemic terminal epoxides, -epoxides, and anhydrides mediated by the privileged chiral dinuclear Al(III) catalyst system, to afford optically active polyester terpolymers with either gradient or random distribution as determined by the epoxides employed during their preparation. The enantioselective terpolymerization of racemic -butyl glycidyl ether (-TBGE) and cyclopentene oxide with phthalic anhydride (PA) or naphthyl anhydride (NA) gives novel gradient polyesters, in which the crystallization behavior varies continuously along the main chain, due to the decrement of one ester component and the increment of the other occurring sequentially from one chain end to the other.

Reversible Transformation between Amorphous and Crystalline States of Unsaturated Polyesters by Cis-Trans Isomerization.

An aliphatic polyester has been prepared from ethylene oxide and maleic anhydride that undergoes reversible transformation between amorphous (T =18 °C) and crystalline (T =124 °C) states through cis-trans isomerization of the C=C bonds in the polymer backbone without any change in either the molecular weight or dispersity of the polymer. A similar transformation was also observed in chiral unsaturated polyesters formed from enantiopure terminal epoxides, such as epichlorohydrin, phenyl glycidyl ether, and (2,3-epoxypropyl)benzene. These unsaturated polyesters with 100 % E-configuration in the crystalline state were prepared by quantitative isomerization of their Z-configuration analogues in the presence of a catalytic amount of diethylamine, while in the presence of benzophenone, irradiation with 365 nm UV light resulted in the transformation of about 30 % trans-alkene to cis-maleate form, thereby affording amorphous polyesters.

Enantioselective Resolution Copolymerization of Racemic Epoxides and Anhydrides: Efficient Approach for Stereoregular Polyesters and Chiral Epoxides.

Herein we report an efficient strategy for preparing isotactic polyesters and chiral epoxides via enantioselective resolution copolymerization of racemic terminal epoxides with anhydrides, mediated by enantiopure bimetallic complexes in conjunction with a nucleophilic cocatalyst. The chirality of both the axial linker and the diamine backbones of the ligand are responsible for the chiral induction of this kinetic resolution copolymerization process. The catalyst systems exhibit exceptional levels of enantioselectivity with a kinetic resolution coefficient exceeding 300 for various racemic epoxides, affording highly isotactic copolymers (selectivity factors of more than 300) with a completely alternating structure and low polydispersity index.

Highly efficient conversion of CO to cyclic carbonates with a binary catalyst system in a microreactor: intensification of "electrophile-nucleophile" synergistic effect.

An intensification of the "electrophile-nucleophile" synergistic effect was achieved in a microreactor for the coupling reaction of CO and epoxides mediated by the binary Al complex/ternary ammonium salt catalyst system. The microreactor technology is proven to be a powerful tool for the preparation of cyclic carbonates with an improved reaction rate and a wide substrate scope.

Precise Synthesis of Poly(thioester)s with Diverse Structures by Copolymerization of Cyclic Thioanhydrides and Episulfides Mediated by Organic Ammonium Salts.

The precise synthesis of poly(thioester)s with diverse structures is still a significant challenge in the polymeric materials field. Herein, we report a novel approach to the synthesis of well-defined poly(thioester)s by the controlled alternating copolymerization of cyclic thioanhydrides and episulfides induced by simple organic ammonium salts. Both the cation and anion have strong effects on the copolymerization.