Dimethyl Carbonate as a Sacrificial Molecule for the Synthesis of 5‐Memebered N‐ and O‐Heterocycles

In the last twenty years DMC has been employed as an efficient methylating and methoxycarbonylating agent with several monodentate and bidentate nucleophiles, showing great selectivity and unexpected results. In this short review we report on yet another application of DMC chemistry i.e. the synthesis of 5‐membered N‐ and O‐heterocycles. In these reactions DMC acts as a sacrificial molecule since it is not present in the final products, but only in the reaction intermediates as an halogen‐free leaving group. This DMC‐based synthesis of heterocycles resulted of general application, as it is effective for aliphatic and aromatic 1,4‐diols, incorporating several functionalities (primary, secondary, tertiary, allylic, phenolic), as well as, for bifunctional compounds i.e. 4‐amino‐1‐butanol. This synthetic procedure was also employed for industrially relevant compounds such as (‐)‐norlabdane oxide and isosorbide showing to maintain the chiral integrity of the substrate. In one case intramolecular cyclisation of isosorbide was also observed to achieve a strained tricyclic derivative. Comparing this reaction methodology with a chlorine based procedure, the DMC‐mediated pathway is quantitative, occurs in one step, does not require any chlorine‐based chemical or strong acid and does not produce any chlorinated waste material.     

Rational Design of an Ionic Liquid‐Based Electrolyte with High Ionic Conductivity Towards Safe Lithium/Lithium‐Ion Batteries

It is a very urgent and important task to improve the safety and high‐temperature performance of lithium/lithium‐ion batteries (LIBs). Here, a novel ionic liquid, 1‐(2‐ethoxyethyl)‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR_1(2o2)TFSI), was designed and synthesized, and then mixed with dimethyl carbonate (DMC) as appropriate solvent and LiTFSI lithium salt to produce an electrolyte with high ionic conductivity for safe LIBs. Various characterizations and tests show that the highly flexible ether group could markedly reduce the viscosity and provide coordination sites for Li‐ion, and the DMC could reduce the viscosity and effectively enhance the Li‐ion transport rate and transference number. The electrolyte exhibits excellent electrochemical performance in Li/LiFeO₄ cells at room temperature as well as at a high temperature of 60 °C. More importantly, with the addition of DMC, the IL‐based electrolyte remains nonflammable and appropriate DMC can effectively inhibit the growth of lithium dendrites. Our present work may provide an attractive and promising strategy for high performance and safety of both lithium and lithium‐ion batteries.     

Reactions of Dimethoxycarbene with N‐Tosylated Imines

The reactions of dimethoxycarbene (DMC; 2 ), which was generated in situ by thermal decomposition of 2,5‐dihydro‐2,2‐dimethoxy‐5,5‐dimethyl‐1,3,4‐oxadiazole ( 1 ), with N‐tosylated imines of xanthone and 2,3 : 6,7‐dibenzosuberenone, 3a and 3d , respectively, led to different adducts with rearranged skeletons. In the case of 3a , the 1 : 1 adduct 5 as well as the 2 : 1 adduct 6 were obtained (Scheme 2). The formation of both products can be explained by a migration of a MeO group of the DMC fragment in a zwitterionic intermediate. On the other hand, migration of a Me group of DMC is necessary for the formation of the two 1 : 1 adducts 13 and 14 of 2 and 3d (Scheme 5). The structures of all products have been established by X‐ray crystallography.     

Effect of n‐type doping on the hole transport in poly(p‐phenylene vinylene)

N‐type doping of poly(2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐p‐phenylene vinylene) (MEH‐PPV) with decamethylcobaltocene (DMC) strongly improves the electron transport due to filling of the electron traps. Unexpectedly, the n‐type doping simultaneously suppresses the hole transport in MEH‐PPV. We demonstrate that this strong reduction of the hole transport originates from unionized DMC molecules that act as hole traps. This hole trapping effect explains why the current of a DMC‐doped MEH‐PPV polymer light‐emitting diode is orders of magnitude lower than that of the undoped device. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Barrier heights of hydrogen‐transfer reactions with diffusion quantum monte carlo method

Hydrogen‐transfer reactions are an important class of reactions in many chemical and biological processes. Barrier heights of H‐transfer reactions are underestimated significantly by popular exchange–correlation functional with density functional theory (DFT), while coupled‐cluster (CC) method is quite expensive and can be applied only to rather small systems. Quantum Monte‐Carlo method can usually provide reliable results for large systems. Performance of fixed‐node diffusion quantum Monte‐Carlo method (FN‐DMC) on barrier heights of the 19 H‐transfer reactions in the HTBH38/08 database is investigated in this study with the trial wavefunctions of the single‐Slater–Jastrow form and orbitals from DFT using local density approximation. Our results show that barrier heights of these reactions can be calculated rather accurately using FN‐DMC and the mean absolute error is 1.0 kcal/mol in all‐electron calculations. Introduction of pseudopotentials (PP) in FN‐DMC calculations improves efficiency pronouncedly. According to our results, error of the employed PPs is smaller than that of the present CCSD(T) and FN‐DMC calculations. FN‐DMC using PPs can thus be applied to investigate H‐transfer reactions involving larger molecules reliably. In addition, bond dissociation energies of the involved molecules using FN‐DMC are in excellent agreement with reference values and they are even better than results of the employed CCSD(T) calculations using the aug‐cc‐pVQZ basis set. © 2017 Wiley Periodicals, Inc.     

Reactions of Polycyclic Ketones with Dimethoxycarbene; a Convenient Route for a ‘One‐Pot’ Preparation of Some α‐Hydroxycarboxylic Acid Esters

Polycyclic ‘cage’ ketones, such as pentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecan‐8‐one ( 10 ), pentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecane‐8,11‐dione ( 11 ), and adamantan‐2‐one ( 16 ) were treated with the nucleophilic dimethoxycarbene (DMC; 1 ), which was generated thermally from 2,5‐dihydro‐2,2‐dimethoxy‐5,5‐dimethyl‐1,3,4‐oxadiazole ( 4a ) in boiling toluene. In this ‘one‐pot’ procedure, the α‐hydroxycarboxylic acid ester 12 or a corresponding derivative 15 or 17 was obtained (Schemes 4–7). Additionally, ‘cage’ thione 21 was treated with DMC under the same conditions yielding dimethoxythiirane 22 (Scheme 8). Subsequent hydrolysis or desulfurization (followed by hydrolysis on silica gel) of 22 gave α‐mercaptocarboxylate 25 and the corresponding desulfurized ester 24 , respectively. In all cases, the addition of DMC occurred stereoselectively, and the addition from the exo‐face is postulated to explain the structures of the isolated products.     

Facile synthesis of poly(DMC‐co‐HPA) hydrogels via infrared laser ignited frontal polymerization and their adsorption–desorption switching performance

In this work, we report a versatile infrared laser ignited frontal polymerization technique for the fabrication of a series of poly(DMC‐co‐HPA) hydrogels (DMC = methacryloxyethyltrimethyl ammonium chloride, HPA = hydroxypropyl acrylate). Because the method is based on the exothermic reaction, no further energy is required in the reaction once it is initiated. Moreover, we have found the polymerization process is a pure frontal polymerization model without involving any other reaction process. The dependence of frontal velocity and temperature on the reaction time is thoroughly discussed. The as‐prepared hydrogels are pH‐responsive and their maximum equilibrium swelling ratio could reach ～3,890%. Also, the as‐prepared poly(DMC‐co‐HPA) hydrogels capable of adsorption/desorption switching performance can be utilized for heavy metal ion removal in wastewater treatments. Interestingly, the hydrogels can float on the water surface after intaking heavy metal ions by the combination of kerosene and polyoxyethylene sorbitan monolaurate (Tween 20) in hydrogel components, greatly enhancing treatment efficiency. We believe the method described herein to rapidly construct functional hydrogels with the ability to remove heavy metal ions may find unique applications in emergency processing of water pollution. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2085–2093     

Ring‐Opening Polymerization of Propylene Oxide by Double Metal Complex in Micro‐Reactor

The ring‐opening polymerization of propylene oxide catalyzed by double metal complex (DMC) is carried out in continuous micro‐reactor (C‐MR). It is found that the monomer conversion at the C‐MR outlet is usually 100% within 2 min of average residence time, which means that the polymerization rate in the C‐MR is faster than that in a traditional semi‐continuous tank reactor. However, the induction period still exists in the polymerization in C‐MR, but can be shortened by increasing the reaction temperature or the micro‐reactor length. The mechanism of monomer coordination and ring opening on DMC during the induction period is confirmed by the ¹H NMR analysis of the samples obtained under very short average residence time. The molecular weight distribution (MWD) of product from C‐MR is generally narrow, which indicates that the process still maintain the characteristics of the “living” polymerization. That is, there is a very high rate ratio of chain transfer to chain propagation provided by the DMC catalyst. However, with the same average residence time, the MWD of product from the longer C‐MR is broader, which can be attributed to the increase of the chain propagation rate caused by rise of pressure.     

An Environmentally Friendly Method for N‐Methylation of 5‐Substituted 1H‐Tetrazoles with a Green Methylating Reagent: Dimethyl Carbonate

An environmentally friendly method was established for the N‐methylation of the 5‐substituted 1H‐tetrazoles with a green reagent: DMC. DABCO was the optimal catalyst, and hazardous chemicals were avoided in this protocol. A plausible catalytic mechanism is proposed, which consists of a DABCO‐activated process and a thermally induced rearrangement of tetrazole carbamates.     

Ethylene Polymerization‐Induced Self‐Assembly (PISA) of Poly(ethylene oxide)‐block‐polyethylene Copolymers via RAFT

Poly(ethylene oxide) (PEO) with dithiocarbamate chain ends (PEO–SC(=S)?N(CH₃)Ph and PEO–SC(=S)?NPh₂, named PEO‐1 and PEO‐2 , respectively) were used as macromolecular chain‐transfer agents (macro‐CTAs) to mediate the reversible addition–fragmentation chain transfer (RAFT) polymerization of ethylene in dimethyl carbonate (DMC) under relatively mild conditions (80 °C, 80 bar). While only a slow consumption of PEO‐1 was observed, the rapid consumption of PEO‐2 led to a clean chain extension and the formation of a polyethylene (PE) segment. Upon polymerization, the resulting block copolymers PEO‐b‐PE self‐assembled into nanometric objects according to a polymerization‐induced self‐assembly (PISA).     

The Complexed 1,3‐Diphospha‐2‐Arsaallyl Radical and Its Cationic and Anionic Derivatives

Photolysis of [Cp*As{W(CO)₅}₂] ( 1 a ) in the presence of Mes*P?PMes* (Mes*=2,4,6‐tri‐tert‐butylphenyl) leads to the novel 1,3‐diphospha‐2‐arsaallyl radical [(CO)₅W(μ,η²:η¹‐P₂AsMes*₂)W(CO)₄] ( 2 a ). The frontier orbitals of the radical 2 a are indicative of a stable π‐allylic system that is only marginally influenced by the d orbitals of the two tungsten atoms. The SOMO and the corresponding spin density distribution of the radical 2 a show that the unpaired electron is preferentially located at the two equivalent terminal phosphorus atoms, which has been confirmed by EPR spectroscopy. The protonated derivative of 2 a , the complex [(CO)₅W(μ,η²:η¹‐P₂As(H)Mes*₂)W(CO)₄] ( 6 a ) is formed during chromatographic workup, whereas the additional products [Mes*P?PMes*{W(CO)₅}] as the Z‐isomer ( 3 ) and the E‐isomer ( 4 ), and [As₂{W(CO)₅}₃] ( 5 ) are produced as a result of a decomposition reaction of radical 2 a . Reduction of radical 2 a yields the stable anion [(CO)₅W(μ,η²:η¹‐P₂AsMes*₂)W(CO)₄]^? in 7 a , whereas upon oxidation the corresponding cationic complex [(CO)₅W(μ,η²:η¹‐P₂AsMes*₂)W(CO)₄][SbF₆] ( 8 a ) is formed, which is only stable at low temperatures in solution. Compounds 2 a , 7 a , and 8 a represent the hitherto elusive complexed redox congeners of the diphospha‐arsa‐allyl system. The analogous oxidation of the triphosphaallyl radical [(CO)₅W(μ,η²:η¹‐ P₃Mes*₂)W(CO)₄] ( 2 b ) also leads to an allyl cation, which decomposes under CH activation to the phosphine derivative [(CO)₅W{μ,η²:η¹‐P₃(Mes*)(C₅H₂tBu₂C(CH₃)₂CH₂)}W(CO)₄] ( 9 ), in which a CH bond of a methyl group of the Mes* substituent has been activated. All new products have been characterized by NMR spectrometry and IR spectroscopy, and compounds 2 a , 3 , 6 a , 7 a , and 9 by X‐ray diffraction analysis.     

Lewis Acid‐Mediated Addition of Amino Acid‐Substituted α‐Allylsilanes to Aromatic Acetals

Unnatural amino acids extend the pharmacological formulator's toolkit. Strategies to prepare unnatural amino acid derivatives using Lewis acid‐activated allylsilane reactions are few. In this regard, we examined the utility of allylsilanes bearing an amino acid substituent in the reaction. Diastereoselective addition of methyl 2‐(N‐PG‐amino)‐3‐(trimethylsilyl)pent‐4‐enoate and methyl (E)‐2‐(N‐PG‐amino)‐3‐(trimethylsilyl)hex‐4‐enoate (PG=protecting group), 2 and 13 , respectively, to aromatic acetals in the presence of Lewis acids is described. Of those examined, TiCl₄ was found to be the most effective Lewis acid for promoting the addition. At least 1 equiv. of TiCl₄ was required to achieve high yields, whereas 2 equiv. of BF₃?OEt₂ were required for comparable outcomes. Excellent selectivity (>99% syn/anti) and high yield (up to 89%) were obtained with halo‐substituted aromatic acetals, while more electron‐rich electrophiles led to both lower yields and diastereoselectivities.     

Facile preparation and synergy study of DMC/ZnGA composite catalyst for the synthesis of oligo (propylene‐carbonate) diols

To overcome the weak carbon dioxide (CO₂) conversion ability of Zn‐Co double metal cyanide (DMC) catalyst, zinc glutarate (ZnGA) catalyst was introduced into the DMC catalytic system and applied for the synthesis of oligo (propylene‐carbonate) diols. The DMC/ZnGA composite catalyst (mass ratio = 10:1) exhibited an excellent synergistic effect which had enhanced CO₂ activation ability, high yield and good selectivity. In copolymerization process, ZnGA catalyst not only provided activated CO₂ for DMC catalyst, but also transferred the propagating chain with more alternating structures to DMC catalyst. Both of the two effects increased the carbonate content in the final products. Overall, DMC catalyst dedicated to the polymer chain growth, while the increased CO₂ conversion mainly attributed to ZnGA catalyst. Oligo (propylene‐carbonate) diols with carbonate unit content of 45.1 mol%, Mn of 1228 g/mol, W_PC of 4.3 wt% and high yield of 1689 g/g _cat was obtained.     

Selective O‐allylation of bisphenol A: toward a chloride‐free route for epoxy resins

The O‐allylation of bisphenol A (BPA) has been performed with the most selective catalysts for O‐allylation of phenols reported previously. Both the cyclopentadienyl–ruthenium catalysts and the palladium–diphosphine catalysts are capable of selectively performing single and double O‐allylation of BPA. An intriguing solvent effect is observed; the choice of the solvent is of key importance for both conversion and selectivity. The use of an excess of diallyl ether as allylating agent results in relatively high yields of the bisallyl ether of bisphenol A, while maintaining the high selectivity for O‐allylation. Copyright © 2010 John Wiley & Sons, Ltd.     

Diarylprolinol‐Mediated Asymmetric Direct Cross‐Aldol Reaction of α,β‐Unsaturated Aldehyde as an Electrophilic Aldehyde

The diarylprolinol‐mediated asymmetric direct cross‐aldol reaction of α,β‐unsaturated aldehyde as an electrophilic aldehyde was developed. The reaction becomes accelerated by an acid when a carbonyl group is introduced at the γ‐position of the α,β‐unsaturated aldehyde. Synthetically useful γ,δ‐unsaturated β‐hydroxy aldehydes were obtained with high anti‐selectivity and excellent enantioselectivity.     

Insertion Homo‐ and Copolymerization of Diallyl Ether

The previously unresolved issue of polymerization of allyl monomers CH₂?CHCH₂X is overcome by a palladium‐catalyzed insertion polymerization of diallyl ether as a monomer. An enhanced 2,1‐insertion of diallyl ether as compared to mono‐allyl ether retards the formation of an unreactive five‐membered cyclic O‐chelate (after 1,2‐insertion) that otherwise hinders further polymerization, and also enhances incorporation in ethylene polymers (20.4 mol %). Cyclic ether repeat units are formed selectively (96 %–99 %) by an intramolecular insertion of the second allyl moiety of the monomer. These features even enable a homopolymerization to yield polymers (poly‐diallyl ether) with degrees of polymerization of DP_n≈44.     

Partially bio‐based tri‐ and hexaallyl monomers: Synthesis from naturally occurring myo‐inositol and polyaddition with dithiols

myo‐Inositol, a naturally occurring cyclic hexaol, was converted to 2,4,6‐tri‐O‐allyl‐myo‐inositol and 1,2,3,4,5,6‐hexa‐O‐allyl‐myo‐inositol. Polyaddition of the former product, a tri(allyl ether) bearing three hydroxyl groups, with dithiols yielded the corresponding networked polymers. Their glass transition temperatures (T_gs) were higher than those of networked polymers formed by the polyaddition of 1,3,5‐tri‐O‐methyl‐2,4,6‐tri‐O‐allyl‐myo‐inositol. This implied the reinforcement of the networks by hydrogen bonding between the hydroxyl groups. Polyaddition of the latter product, a hexa(allyl ether), with dithiols yielded the corresponding networked polymers with much higher T_gs than those of all of the aforementioned networked polymers. This implied that efficient use of the hexafunctional monomer leads to the formation of more densely crosslinked polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1524–1529     

Transition‐Metal‐Free Borylation of Allylic and Propargylic Alcohols

The base‐catalyzed allylic borylation of tertiary allylic alcohols allows the synthesis of 1,1‐disubstituted allyl boronates, in moderate to high yield. The unexpected tandem performance of the Lewis acid–base adduct, [Hbase]⁺[MeO‐B₂pin₂]^? favored the formation of 1,2,3‐triborylated species from the tertiary allylic alcohols and 1‐propargylic cyclohexanol at 90 °C.     

Efficient Total Synthesis of (S)‐14‐Azacamptothecin

An efficient total synthesis of (S)‐14‐azacamptothecin has been accomplished in 10 steps and 56 % overall yield from 5H‐pyrano[4,3‐d]pyrimidine 8 . A mild Hendrickson reagent‐triggered intramolecular cascade cyclization, a highly enantioselective dihydroxylation, and an efficient palladium‐catalyzed transformation of an O‐allyl into N‐allyl group are the key steps in the synthesis. This work provides a much higher overall yield than the previous achievement and shows sound flexibility for the further applications that will lead to new bioactive analogues.     

Synthesis and characterization of amphiphilic block copolymers with allyl side‐groups

The synthesis of a new cyclic carbonate monomer containing an allyl group was reported and its biodegradable amphiphilic block copolymer, poly(ethylene glycol)‐block‐poly(L ‐lactide‐co‐5‐methyl‐5‐allyloxycarbonyl‐propylene carbonate) [PEG‐b‐P(LA‐co‐MAC)] was synthesized by ring‐opening polymerization (ROP) of L ‐lactide (LA) and 5‐methyl‐5‐allyloxycarbonyl‐1,3‐dioxan‐2‐one (MAC) in the presence of poly (ethylene glycol) as a macroinitiator, with diethyl zinc as a catalyst. ¹³C NMR and ¹H NMR were used for microstructure identification of the copolymers. The copolymer could form micelles in aqueous solution. The core of the micelles is built of the hydrophobic P(LA‐co‐MAC) chains, whereas the shell is set up by the hydrophilic PEG blocks. The micelles exhibited a homogeneous spherical morphology and unimodal size distribution. By using the cyclic carbonate monomer containing allyl side‐groups, crosslinking of the PEG‐b‐P(LA‐co‐MAC) inner core was possible. The adhesion and spreading of ECV‐304 cells on the copolymer were better than that on PLA films. Therefore, this biodegradable amphiphilic block copolymer is expected to be used as a biomaterial for drug delivery and tissue engineering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5518–5528, 2007