Positional and Geometrical Isomerisation of Alkenes: The Pinnacle of Atom Economy

Strategies to achieve spatiotemporal regulation of pre‐existing alkenes via external stimuli are essential given the ubiquity of feedstock olefins in chemistry and their downstream applications. Mirroring the 1‐0 switch that underpins mammalian vision through selective geometric isomerisation in retinal, strategies to manipulate 2D space by both geometric and positional isomerisation of alkenes via chemical, thermal and light‐driven processes are being intensively pursued. This minireview highlights the current state of the art in activating and achieving directionality in these fundamental chemical transformations.     

Hydrochlorofluoromethylation of unactivated alkenes with chlorofluoroacetic acid

An operationally simple method enabling hydrochlorofluoromethylation of unactivated alkenes under visible light activation is reported. The procedure has various benefits. It uses commercially available and inexpensive chlorofluoroacetic acid and phenyliodine(III) diacetate for the generation of the required chlorofluoromethyl radical, it converts feedstock olefins into attractive 1-chloro-1-fluoroalkanes, and it tolerates a broad variety of functional groups. The chlorofluoromethyl radical has a reactivity profile towards alkenes similar to the nucleophilic difluoromethyl radical.     

Copper‐Catalyzed Enantioselective Markovnikov Protoboration of α‐Olefins Enabled by a Buttressed N‐Heterocyclic Carbene Ligand

Reported is a highly enantioselective copper‐catalyzed Markovnikov protoboration of unactivated terminal alkenes. A variety of simple and abundant feedstock α‐olefins bearing a diverse array of functional groups and heterocyclic substituents can be used as substrates, and the reaction proceeds under mild reaction conditions at ambient temperature to provide expedient access to enantioenriched alkylboronic esters in good regioselectivity and with excellent enantiocontrol. Critical to the success of the protocol was the development and application of a novel, sterically hindered N‐heterocyclic carbene, (R,R,R,R)‐ANIPE, as the ligand for copper.     

Intrazeolite photooxidations of electron-poor alkenes

The inability of the intrazeolite environment to influence the regiochemistry of addition of singlet oxygen to electron-poor olefins is reported. This divergent behavior with respect to electron-rich alkenes is rationalized with a multicomplexation model that emphasizes the importance of intrazeolite substrate-cation binding.     

NiH‐Catalyzed Reductive Relay Hydroalkylation: A Strategy for the Remote C(sp3)−H Alkylation of Alkenes

The terminal‐selective, remote C(sp³)?H alkylation of alkenes was achieved by a relay process combining NiH‐catalyzed hydrometalation, chain walking, and alkylation. This method enables the construction of unfunctionalized C(sp³)?C(sp³) bonds under mild conditions from two simple feedstock chemicals, namely olefins and alkyl halides. The practical value of this transformation is further demonstrated by the large‐scale and regioconvergent alkylation of isomeric mixtures of olefins at low catalyst loadings.     

Methods for the Preparation of Bridgehead Olefins

During the past eight years, bridgehead olefins have attracted rapidly increasing attention. In view of their significance with regard to the stereochemistry of alkenes, the study of certain reaction mechanisms, and the nature of the double bond, detailed research into this structural type appears highly desirable. Bridgehead olefins represent connective linkages between olefins in the ground state and species which can arise in the deactivation of photochemically excited alkenes and cycloalkenes and also contribute to our understanding of the structural conditions prevailing during cis-trans isomerization of alkenes.     

Difunctionalization of Alkenes Involving Metal Migration

The direct difunctionalization of alkenes, a cheap and abundant feedstock, represents one of the most attractive strategies for increasing molecular complexity in synthetic organic chemistry. In contrast with the 1,2‐difunctionalization of alkenes, recent advances showcase alkene 1,n‐difunctionalizations (n≠2) involving metal migration is an emerging and rapidly growing area of research. This promising strategy not only opens a novel avenue for future development of alkene transformations, but also significantly expands upon the bond disconnections available in modern organic synthesis. This Minireview summarizes recent progress in the migratory difunctionalization of alkenes, with an emphasis on the driving force for metal migration.     

Immobilization and Continuous Recycling of Photoredox Catalysts in Ionic Liquids for Applications in Batch Reactions and Flow Systems: Catalytic Alkene Isomerization by Using Visible Light

A catalytic (E)‐ to (Z)‐isomerization of olefins using a photoredox catalyst under mild reaction conditions is presented. A variety of (Z)‐alkenes can be prepared in the presence of visible light. A new reaction system allows an easy and efficient scale‐up, as well as a continuous flow process in which the photocatalyst is immobilized in an ionic liquid and continuously recycled by simple phase separation.     

Photo- and Electrochemical Cobalt Catalysed Hydrogen Atom Transfer for the Hydrofunctionalisation of Alkenes

Catalytic hydrogen atom transfer from metal-hydrides to alkenes allows feedstock olefins to be used as alkyl radical precursors. The chemoselectivity of this process makes it an attractive synthetic tool and as such it has been regularly used in synthesis of complex molecules. However, onwards reactivity is limited by compatibility with the conditions which form the key metal-hydride species. Now, through the merger with photocatalysis or electrochemistry, milder methods are emerging which can unlock entirely new reactivity and offer perspectives on expanding these methods in unprecedented directions. This review outlines the most recent developments in electro- and photochemical cobalt catalysed methods and offers suggestions on the future outlook.     

Production of Low-carbon Light Olefins from Catalytic Cracking of Crude Bio-oil

Low-carbon light olefins are the basic feedstocks for the petrochemical industry. Catalytic cracking of crude bio-oil and its model compounds (including methanol, ethanol, acetic acid, acetone, and phenol) to light olefins were performed by using the La/HZSM-5 catalyst. The highest olefins yield from crude bio-oil reached 0.19 kg/(kg crude bio-oil). The reaction conditions including temperature, weight hourly space velocity, and addition of La into the HZSM-5 zeolite can be used to control both olefins yield and selectivity. Moderate adjusting the acidity with a suitable ratio between the strong acid and weak acid sites through adding La to the zeolite effectively enhanced the olefins selectivity and improved the catalyst stability. The production of light olefins from crude bio-oil is closely associated with the chemical composition and hydrogen to carbon effective ratios of feedstock. The comparison between the catalytic cracking and pyrolysis of bio-oil was studied. The mechanism of the bio-oil conversion to light olefins was also discussed.     

Catalytic Cracking of Lower-Valued Hydrocarbons for Producing Light Olefins

A number of important chemicals are made from light olefins such as propylene and ethylene, and it is expected that market demand for these light olefins will continue to grow at 4–5% annually, and the average overall growth of propylene will be about 1% higher than that of ethylene. From the viewpoint of supply of feedstock and demand of light olefins, it is anticipated that the thermal cracking process of naphtha will be gradually transformed to a catalytic process such as ACO^TM that can efficiently produce both ethylene and propylene in high yield. Also, together with primary light olefin production technologies utilizing heavy feedstocks such as DCC^TM, and HPFCC, supplementary propylene production technologies utilizing C₄–C₄ such as SUPERFLEX^TM, MOI^TM, and PROPYLUR^TM will be applied gradually in commercial production.     

Review of Directly Producing Light olefins via CO Hydrogenation

Directly making light olefins via CO hydrogenation is a promising process to obtain a nonpetroleum based supply of alkenes.Limited by the ASF distribution function of Fischer-Tropsch synthesis,the yield of light olefins (C2-C4) can not reach the desired levels,which is a great challenge to overcome.Beginning thermodynamic analysis,the ASF distribution function,the reaction performance of CO hydrogenation and slurry reactor studies.The problems currently faced by this research area are presented at the end of the article.     

PRODUCTION OF LIGHT ALKENES FROM CO AND/OR CO_2 HYDROGENATION OVER K-Fe-MnO/SILICALITE-2 CATALYST

High selectivity to light alkenes can be achieved from CO and CO_2hydrogenation over K-Fe-MnO/Si-2 catalyst.The alkene selectivity isinsensitive to reaction temperature for CO hydrogenation,while apparentlyincreases for CO_2 hydrogenation with raising reaction temperature.An increasein alkene selectivity is observed for both CO and CO_2 hydrogenation with GHSVrising,While a decrease with the elevation of reaction pressure for both CO/H_2and CO_2/H_2 reaction.A two-step mechanism is suggested forCO_2 hydrogenation to form hydrocarbons,by which the variations incontributions of CO and HC as products of CO_2/H_2 reaction with change ofreaction temperature,GHSV and pressure are explained.Moreover,thecatalyst is favorable for selective production of light olefins,which can alsoconcern the slightly secondary reactions of light olefins to some extent.     

Catalytic Enantioselective Functionalization of Unactivated Terminal Alkenes

Terminal alkenes are readily available functional groups which appear in α‐olefins produced by the chemical industry, and they appear in the products of many contemporary synthetic reactions. While the organic transformations that apply to alkenes are amongst the most studied reactions in all of chemical synthesis, the number of reactions that apply to nonactivated terminal alkenes in a catalytic enantioselective fashion is small in number. This Minireview highlights the cases where stereocontrol in catalytic reactions of 1‐alkenes is high enough to be useful for asymmetric synthesis.     

Visible light-promoted metal-free aerobic oxyphosphorylation of olefins: A facile approach to β-ketophosphine oxides

A metal-free direct aerobic oxyphosphorylation of alkenes with H-phosphine oxides has been developed utilizing visible light photoredox catalysis. A variety of β-ketophosphine oxides have been obtained in good yields from simple olefins under air with inexpensive rhodamine B as the non-metallic photocatalyst. This method provides a mild, green, and practical synthetic approach to valuable β-ketophosphine oxides.     

Expedient Synthesis of Ketones via N‐Heterocyclic Carbene/Nickel‐Catalyzed Redox‐Economical Coupling of Alcohols and Alkynes†

An N‐heterocyclic carbene/nickel‐catalyzed direct coupling of alcohols and internal alkynes to form α‐branched ketones has been developed. This methodology provides a new approach to afford branched ketones, which are difficult to access through the hydroacylation of simple internal alkenes with aldehydes. This redox‐neutral and redox‐economical coupling is free from any oxidative or reductive additives as well as stoichiometric byproducts. These reactions convert both benzylic and aliphatic alcohols and alkynes, two basic feedstock chemicals, into various α‐branched ketones in a single chemical step.     

Iron(III) porphyrin catalyzed aziridination of alkenes with bromamine-T as nitrene source

[reaction: see text] Iron(III) porphyrin complexes Fe(Por)Cl are effective catalysts for aziridination of alkenes using bromamine-T as the nitrene source. The catalytic system can operate under mild conditions with alkenes as limiting reagents. The aziridination reaction is general and suitable for a wide variety of alkenes, including aromatic, aliphatic, cyclic, and acyclic olefins, as well as alpha,beta-unsaturated esters. For 1,2-disubstituted olefins, the reactions proceeded with moderate to low stereospecificity.     

Iron‐Catalyzed Regioselective Transfer Hydrogenative Couplings of Unactivated Aldehydes with Simple Alkenes

An FeBr₃‐catalyzed reductive coupling of various aldehydes with alkenes that proceeds through a direct hydride transfer pathway has been developed. With ⁱPrOH as the hydrogen donor under mild conditions, previously challenging coupling reactions of unactivated alkyl and aryl aldehydes with simple alkenes, such as styrene derivatives and α‐olefins, proceeded smoothly to furnish a diverse range of functionalized alcohols with complete linear regioselectivity.     

Broadly Applicable Z‐ and Diastereoselective Ring‐Opening/Cross‐Metathesis Catalyzed by a Dithiolate Ru Complex

A broadly applicable Ru‐catalyzed protocol for Z‐selective ring‐opening/cross‐metathesis (ROCM) is disclosed. In addition to reactions relating to terminal alkenes of different sizes, the first examples of Z‐selective ROCM processes involving heteroaryl olefins, 1,3‐dienes, and O‐ and S‐substituted alkenes as well as allylic and homoallylic alcohols are reported. Z‐Selective transformations with an α‐substituted allylic alcohol are shown to afford congested Z alkenes with high diastereoselectivity. Transformations are performed in the presence of 2.0–5.0 mol % of a recently disclosed Ru‐based dithiolate complex that can be easily prepared in a single step from commercially available starting materials. Typically, transformations proceed at ambient temperature and are complete within eight hours; products are obtained in up to 97 % yield, >98:2 Z/E, and >98:2 diastereomeric ratio. The present investigations reveal a mechanistically significant attribute of the Ru‐based dithiolates that arises from electrostatic interactions with anionic S‐based ligands.     

纳米ZSM-5用于石脑油催化裂化的最新进展(英文)

综述了纳米ZSM-5在石脑油催化裂解中的应用.比较了纳米ZSM-5和毫米级ZSM-5对产物选择性、反应转化率和催化剂寿命的影响.纳米ZSM-5的应用不仅延长了催化剂寿命,而且表现出更稳定的轻质烯烃选择性.讨论了反应条件,如温度和进料对纳米ZSM-5催化性能的影响,发现高温和线式烷烃作为进料时可提高轻质烯烃的选择性和反应转化率.