Enantioselective synthesis of chiral phosphonylated 2,3-dihydrofurans by copper catalyzed asymmetric formal [3+2] cycloaddition of propargylic esters with β-keto phosphonates

Copper catalyzed asymmetric formal [3＋2] cycloaddition of propargylic esters toβ‐keto phospho‐nates for the synthesis of chiral phosphonylated 2,3‐dihydrofurans was developed. By using a bulky and structurally rigid tridentate ketimine P,N,N ligand, a series of optically active phosphonylated 2,3‐dihydrofurans were prepared in high yield and up to 92%ee.

Environmentally friendly, microwave-assisted synthesis of 5-substituted 1H-tetrazoles by recyclable CuO nanoparticles via(3+2) cycloaddition of nitriles and NaN_3

Recyclable CuO nanoparticles were successfully employed to catalyze the microwave‐assisted(3+2)cycloaddition reaction between nitriles and NaN3to efficiently synthesize5‐substituted1H‐tetrazoles.The salient features associated with this protocol are its cost effectiveness,rapid synthesis,stability,reusability,mild reaction conditions without any additives,high tolerance to various functional groups,and excellent yields under microwave irradiation.This environmentally friendly,microwave‐assisted,nanoparticle‐catalyzed synthetic methodology is seen as an alternative to conventional procedures that involve Lewis acid catalysts and a simple operation to the privileged scaffold.

Enantioselective intermolecular[2+2]photocycloadditions of vinylazaarenes with triplet-state electron-deficient olefins

The development of catalytic asymmetric radical reactions is an attractive but formidable task.The high reactivity of radicals enables the use of readily accessible feedstocks and mild reaction conditions,but it leads to substantial difficulty for chiral catalysts to provide sufficient enantiocontrol.Moreover,a racemic background process is often inevitable,further deteriorating enantioselectivity.In this regard,an effective protocol has been established for enantioselective intermolecular[2+2]photocycloadditions to overcome the challenges,which is capitalising on the ground-state preassociations of chiral catalysts with photoactivated substrates.Here,we report the viability of substrate-differentiating synergistic catalysis for this important reaction.In this new platform,energy transfer occurs between DPZ as a photosensitizer and enones or(E)-2-substituted vinylazaarenes for producing triplet-state species,and chiral phosphoric acid interacts with ground-state 2-vinylazaarenes via hydrogen bonding for subsequent enantiofacial cycloaddition.Although all active species are dispersed in the reaction system,valuable enantioenriched mono-and di-azaarene-functionalized cyclobutanes are obtained efficiently and selectively.In addition to constructing all-carbon quaternary stereocentres,flexible modulation of azaaryl groups and other substituents on the cyclobutane ring is also operative.

串联炔-异氰[3+2]环加成/Boulton-Katritzky重排/扩环反应构建吡咯并[3,2-d]嘧啶-4-酮化合物

吡咯并[3,2-d]嘧啶-4-酮骨架在药物设计中广受关注,该骨架是众多生物活性分子的核心结构单元.目前已报道的吡咯并[3,2-d]嘧啶-4-酮骨架的合成方法有限且存在原料不易得、反应条件苛刻、合成步骤长、产率低和产物结构不易修饰等缺陷.因此,发展吡咯并[3,2-d]嘧啶-4-酮骨架的新型高效合成策略在合成化学与药物化学领域均具有重要的研究意义.最近,一种通过串联炔-异氰[3+2]环加成/Boulton-Katritzky重排/酰基迁移扩环反应构建9-去氮鸟嘌呤化合物的新方法被报道,该方法以氮杂异噁唑衍生的炔丙酰胺化合物和异氰化合物为原料.鉴于异噁唑化合物也是Boulton-Katritzky重排反应常使用的底物,此工作进一步研究了一系列异噁唑衍生的炔丙酰胺化合物与异氰化合物的上述串联反应,成功构建了一系列吡咯并[3,2-d]嘧啶-4-酮化合物.

CO_(2) hydrogenation selectivity shift over In‐Co binary oxides catalysts:Catalytic mechanism and structure‐property relationship

The hydrogenation of CO_(2) into methanol has attracted much attention and In_(2)O_(3) is a promising catalyst.Introducing metal elements into In_(2)O_(3)(M/In_(2)O_(3))is one of the main strategies to improve its performance.However,its mechanism and active sites remain unclear and need to be further elucidated.Here,the noble‐metal‐free In_(x)‐Co_(y) oxides catalysts were prepared.Much‐improved performance and obvious product selectivity shift were observed.The optimized catalyst(In_(1)‐Co_(4))(9.7 mmol g_(cat)^(–1) h^(–1))showed five times methanol yields than pure In_(2)O_(3)(2.2 mmol g_(cat)^(–1) h^(–1))(P=4.0 MPa,T=300°C,GHSV=24000 cm^(3)_(STP) g_(cat)^(–1) h^(–1),H_(2):CO_(2)=3).And the cobalt‐catalyzed CO_(2) methanation activity was suppressed,although cobalt was most of the metal element.To unravel this selectivity shift,detailed catalysts performance evaluation,together with several in‐situ and ex‐situ characterizations,were employed on cobalt and In‐Co for comparative study.The results indicated CO_(2) hydrogenation on cobalt and In‐Co catalyst both followed the formate pathway,and In‐Co reconstructed and generated a surface In_(2)O_(3)‐enriched core‐shell‐like structure under a reductive atmosphere.The enriched In_(2)O_(3) at the surface significantly enhanced CO_(2) adsorption capacity and well stabilized the intermediates of CO_(2) hydrogenation.CO_(2) and carbon‐containing intermediates adsorbed much stronger on In‐Co than cobalt led to a feasible surface C/H ratio,thus allowing the*CH_(3)O to desorb to produce CH_(3)OH instead of being over‐hydrogenated to CH_(4).

The synthesis of tetracyclic coumarins via decarboxylative asymmetric[4+2]cycloadditions enabled by Pd(0)/Cu(I)synergistic catalysis

Tetracyclic coumarins are a class of important compounds with diverse and superior pharmacolog‐ical activities.However,a direct stereoselective method from simple and readily‐made coumarins derivatives remains challenging due to the inertness of coumarins as dienophiles.Herein,we de‐velop a decarboxylative asymmetric[4+2]cycloaddition of 3‐cyanocoumarins with vinyl benzoxa‐zinones,affording the coumarin‐derived condensed rings bearing three continuous stereocenters in high yields with excellent diastereoselectivities(>20/1 d.r.)and enantioselectivities(up to 99%ee).This direct enantioselective reaction was achieved by a Pd(0)/Cu(I)bimetallic catalytic system.The mechanism studies indicated that the synergistic activation effect,in which chiral Cu(I)as an availa‐ble Lewis acid catalyst activates 3‐cyanocoumarin and chiral Pd(0)complex activates benzoxazi‐none by the formation ofπ‐allyl‐palladium intermediate,plays an important role on the stereoselec‐tive control.The current work provides a new activation modes of Cu catalyst in the Pd/Cu bimetal‐lic catalytic system.

1,1'-Methylenediimidazolium-Based Multiple Hydrogen-Bond Donor Catalysts Facilitate the Cycloaddition of CO_(2) with Epoxides under Atmospheric Pressure

The quest for innovative hydrogen-bond donor(HBD)catalysts has led to a significant advancement in the field of organic synthesis.Considering the electron-withdrawing strength of imidazolium cations and the spatial requirements of hydrogen bond donors,a novel HBD catalyst based on the 1,1'-methylenediimidazolium scaffold by bridging two imidazolium cations with methylene was developed.The 1,1'-methylenediimidazolium-based catalysts exhibit excellent performance in the cycloaddition reaction of CO_(2) and epoxides,achieving up to 99% yield and 99%selectivity under mild conditions(atmospheric pressure,80℃ for 12 h,with 1 mol%catalyst).The geometric structure,atomic charge distribution,and synergistic effect of HBD catalysts were studied in detail through 1H NMR spectroscopy and density functional theory(DFT)calculations.The research results indicate that the protons at positions C2-H,C2'-H,C5-H,and C5'-H on the imidazolium rings,as well as the protons on the bridged methylene,contribute to the formation of multiple hydrogen bonds with appropriate distance and synergistic effects,which are crucial for activating CO_(2) and epoxides.This research highlights the distinctive attributes of 1,1'-methylenediimidazolium-based catalysts and offers valuable insights into the development of highly efficient multiple HBD catalysts.

Recent advances in application of iron‐based catalysts for CO_(x) hydrogenation to value‐added hydrocarbons

The widespread utilization of fossil fuels has caused an associated increase in CO_(2) emissions over the past few decades,which has resulted in global warming and ocean acidification.CO hydrogenation(Fischer‐Tropsch synthesis,FTS)is considered a significant route for the production of liquid fuels and chemicals from nonpetroleum sources to meet worldwide demand.Conversion of CO_(2) with renewable H_(2) into valuable hydrocarbons is beneficial for reducing dependence on fossil fuels and mitigating the negative effects of high CO_(2) concentrations in the atmosphere.Iron‐based catalysts exhibit superior catalytic performance in both FTS and CO_(2) hydrogenation to value‐added hydrocarbons.The abundance and low cost of iron‐based catalysts also promote their wide application in CO_(x) hydrogenation.This paper provides a comprehensive overview of the significant developments in the application of iron‐based catalysts in these two fields.The active phases,promoter effect,and support of iron‐based catalysts are discussed in the present paper.Based on understanding of these three essential aspects,we also cover recent advances in the design and preparation of novel iron‐based catalysts for FTS and CO_(2) hydrogenation.Current challenges and future catalytic applications are also outlined.

非对称杂化的手性膦-亚磷酰胺酯配体在不对称催化反应中的应用进展

非对称杂化的手性膦-亚磷酰胺酯配体因其合成简便、易于调控、结构稳定等优点,被广泛应用于不对称催化反应中,如:不对称氢化、不对称氢甲酰化、不对称烯丙基烷基化、不对称氢膦酰化、不对称[3+2]-环加成、不对称1,4-加成和1,4-还原反应等.综述了手性膦-亚磷酰胺酯配体的种类、合成及其在不对称催化反应中的应用.

OsO^+氧化活化氢分子气相反应机理的密度泛函理论计算

为了探寻OsO+与H2气相反应的机理,用密度泛函理论方法 UB3LYP,全优化了该反应的加成(氧化加成和[2+2]环加成)-消除、氢抽提-反弹,以及氧端插入等四种可能路径中所有可能的反应物、中间体、过渡态和产物在六重态、四重态和二重态等三个自旋态下的几何结构,计算了各种机理反应的势能面.结果表明,标题反应为自旋禁阻反应,反应起始自四重态,最终产物为六重态基态,整个反应放热21.0 kJ mol-1.因反应络合物相对于入口通道有太正Gibbs函数,氧端插入机理是高能的过程.其他三种机理都具有多(或二)态反应性(MSR或TSR).其中,两种加成-消除机理的最低能量路径都可能经由四重态-二重态-四重态-六重态的三次自旋翻转,抽提-反弹机理的最低能量路径可能经历由四重态-六重态的自旋翻转.抽提-反弹机理由势能面一路攀升的吸热氢抽提过程和几乎无能垒的强放热的反弹过程组成,所以按该机理反应在常温常压下难以发生.两种加成-消去机理的决速步(第二个H的迁移步)相同,虽然其位垒稍高,为156.9 kJ mol-1,但与其进程中前面的强放热步骤耦合,常温常压下该反应是可以发生的.其中,协同环加成步的位垒仅28.7 kJ mol-1,比第一个H的还原消去步的位垒低113.7 kJ mol-1,所以竞争的结果是,常温常压下[2+2]环加成-消去机理比氧化加成-消去机理在动力学上更有利.