Recent advances in annulations enabled by nucleophilic Lewis base/metal dual catalysis

Metal/nucleophilic Lewis base dual catalysis has been recognized as a reliable and promising strategy for finishing ideal organic synthesis over the past decades.The new strategy can usually achieve some chemical reactions that cannot be realized by the traditionally mono-catalytic system,dramatically expanding the synthetic utility of chemical transformations by leveraging additional activation modes.Thus considerable progress has been made in the synthesis of a wide range of heterocyclic and biologically active compounds by using the combination of diversely metal/nucleophilic Lewis base dual catalysts,including metal/phosphine,metal/N-heterocyclic carbene(NHC)and metal/tertiary amine dual catalysis systems.In this review,we describe a comprehensive and updated advance of metal/nucleophilic Lewis base dual catalytic annualtion reactions,meanwhile,the related mechanism and the application of these annulation strategies in natural product total synthesis will be highlighted in detail.

Efficient and stable tin-based perovskite solar cells by introducing π-conjugated Lewis base

Tin-based perovskite solar cells(TPSCs)as the most promising candidate for lead-free PSCs have incurred extensive researches all over the world.However,the crystallization process of tin-based perovskite is too fast during the solution-deposited process,resulting in abundant pinholes and poor homogeneity that cause serious charge recombination in perovskite layer.Here,we employed theπ-conjugated Lewis base molecules with high electron density to systematically control the crystallization rate of FASnI3 perovskite by forming stable intermediate phase with the Sn-I frameworks,leading to a compact and uniform perovskite film with large increase in the carrier lifetime.Meanwhile,the introduction of theπ-conjugated systems also retards the permeation of moisture into perovskite crystal,which significantly suppresses the film degradation in air.These benefits contributed to a stabilizing power conversion efficiency(PCE)of 10.1%for the TPSCs and maintained over 90%of its initial PCE after 1000-h light soaking in air.Also,a steady-state efficiency of 9.2%was certified at the accredited test center.

Recent advances in tertiary amine Lewis base-promoted cycloadditions of allenoates

Lewis base-catalyzed annulations of allenoates have been one of the most powerful synthetic strategies for the synthesis of various valuable cycles,especially in the preparation of biologically active natural products and pharmaceuticals.Generally,the effective Lewis bases mainly include tertiary phosphine,NHC and tertiary amine catalysts,among those catalysis,tertiary amine Lewis bases have proven to be effective catalysts for a range of synthetic transformations.In the past decades,tremendous progress in-volving tertiary amines-promoted cycloaddition of allenoates has been made in the chemoselective con-struction of valuable motifs.This review describes a comprehensive and updated summary of tertiary amine Lewis base-promoted annulation reactions of allenoates.Diverse reactivities,chemoselectivties and detailed reaction mechanisms will be highlighted in this review.

Lewis base catalyzed ring-expansion of isatin with 2,2,2-trifluorodiazoethane(CF3CHN2):An efficient route to3-hydroxy-4-(trifluoromethyl)quinolinones

A Lewis base catalyzed ring expansion of isatin with 2,2,2-trifluorodiazoethane(CF3 CHN2)is developed.It is characterized that the merge of tetramethylethylenediamine and CF3 CHN2 generates reactive triazene intermediates,which construct substituted 3-hydroxy-4-(trifluoromethyl)quinolinones with high efficiency.Synthetic application of the procedure is broadened by 3-trifluormethylpyrazole fused3-hydroxy-4-(trifluoromethyl)quinolinone synthesis.

Boron(III) Tribromide or Titanium(IV) Bromide and Lewis Base Promoted Baylis-Hillman Reaction

It was found that, when the Baylis-Hillman reaction of arylaldehydes withmethyl vinyl ketone was carried out at below - 20℃ in the presence of boron (Ⅲ) tribromide ortitanium (Ⅳ) bromide using a catalytic amount of Lewis base such as amine, the brominated compoundsand the Baylis-Hillman adducts could be obtained as the major products in good yields for variousaryl aldehydes. But at room temperature, the elimination products were the major products. Inaddition, the palladium catalyzed allylic substitution reactions of the e-limination products werealso examined.

Synergistic Copper and Chiral Lewis Base Catalysis for the Asymmetric Synthesis of Pyrrolo[1,2-a]indoles

The first asymmetric decarboxylative[3+2]-cycloaddition of ethynyl indoloxazolidones with carboxylic acids has been developed under synergistic catalysis of copper and chiral Lewis base.This protocol provides a direct and modular approach to biologically important pyrrolo[1,2-a]indoles bearing two vicinal stereogenic centers with excellent diastereo-and enantioselectivities(up to>20:1 dr and>99%ee).In addition,the utility of this methodology was demonstrated by scaled-up reaction and several synthetic transformations of the cycloadduct.

Boosting the polysulfide confinement in B/N–codoped hierarchically porous carbon nanosheets via Lewis acid–base interaction for stable Li–S batteries

Carbon materials have shown remarkable usefulness in facilitating the performance of insulating sulfur cathode for lithium–sulfur batteries owing to their excellent conductivity and porous structure. However,the anxiety is the poor affinity toward polar polysulfides due to the intrinsic nonpolar surface of carbon.Herein, we report a direct pyrolysis of the mixture urea and boric acid to synthesize B/N–codoped hierarchically porous carbon nanosheets(B–N–CSs) as efficient sulfur host for lithium–sulfur battery. The graphene–like B–N–CSs provides high specific surface area and porous structure with abundant micropores(1.1 nm) and low–range mesopores(2.3 nm), thereby constraining the sulfur active materials within the pores. More importantly, the codoped B/N elements can further enhance the polysulfide confinement through strong Li–N and B–S interaction based on the Lewis acid–base theory. These structural superiorities significantly suppress the shuttle effect by both physical confinement and chemical interaction, and promote the redox kinetics of polysulfide conversion. When evaluated as the cathode host, the S/B–N–CSs composite displays the excellent performance with a high reversible capacity up to 772 m A h g–1 at 0.5 C and a low fading rate of ^0.09% per cycle averaged upon 500 cycles. In particular, remarkable stability with a high capacity retention of 87.1% can be realized when augmenting the sulfur loading in the cathode up to 4.6 mg cm^(-2).

An efficient Hauser-base electrolyte for rechargeable magnesium batteries

Rechargeable magnesium batteries(RMBs)are considered the promising candidates for post lithium-ion batteries due to the abundant storage,high capacity,and dendrite-rare characteristic of Mg anode.However,the lack of practical electrolytes impedes the development and application of RMBs.Here,through a one-step reaction of LiCl congenital-containing Knochel–Hauser base TMPL(2,2,6,6-tetrame thylpiperidinylmagnesium chloride lithium chloride complex)with Lewis acid AlCl_(3),we successfully synthesized an efficient amino-magnesium halide TMPLA electrolyte.Raman and mass spectroscopy identified that the electrolyte comprises the typical di-nuclear copolymer[Mg_(2)Cl_(3)·6THF]+cation group and[(TMP)2AlCl_(2)]-anion group,further supported by the results of density functional theory calculations(DFT)and the Molecular dynamics(MD)simulations.The TMPLA electrolyte exhibits promising electrochemical performance,including available anodic stability(>2.65 V vs.SS),high ionic conductivity(6.05mS cm^(-1)),and low overpotential(<0.1 V)as well as appropriate Coulombic efficiency(97.3%)for Mg plating/stripping.Both the insertion Mo6S8cathode and conversion Cu S cathode delivered a desirable electrochemical performance with high capacity and good cycling stability based on the TMPLA electrolyte.In particular,when compatible with low cost and easily synthesized Cu S,the Cu S||Mg cell displayed an extremely high discharge capacity of 458.8 mAh g^(-1)for the first cycle and stabilized at 170.2 mAh g^(-1)with high Coulombic efficiency(99.1%)after 50 cycles at 0.05 C.Our work proposes an efficient electrolyte with impressive compatibility with Mg anode and insertion/conversion cathode for practical RMBs and provides a more profound knowledge of the Lewis acid–base reaction mechanisms.

Remote stereocontrol in the(4+2)cycloadditions of 1,7-zwitterions:Asymmetric synthesis of multifunctionalized tetrahydroquinoline derivatives

The scope of stereochemistry recognition usually occurs near the chiral scaffold of a ligand or catalyst.Remote stereocontrol,which can surpass the limits of stereorecognition of remote prochiral centers,has long been a challenging object of great interest in asymmetric catalysis.The current work realized the remote stereocontrol of 1,7-zwitterion intermediates formed from Huang's o-amino aryl MBH carbonates.With simple and easily accessibleβ-ICD as the bifunctional catalyst,multifunctionalized tetrahydroquinoline derivatives could be synthesized via(4+2)cycloadditions with excellent enantioselectivity and diastereoselectivity under mild conditions.The strategy possesses broad substrate scope,and three types of electron-deficient enones are successfully applied.Mechanistic studies disclosed the Lewis base-catalyzed reaction pathway,and H-bonding between the catalyst and enones is crucial for long-range stereocontrol.Scale-up reaction and transformations of the tetrahydroquinoline products demonstrated the potential of this strategy.

Ethoxylation of Phenols Catalyzed by Metal-Free Lewis Pairs:Living/Controlled Polymerization in a Slow-lnitiation Mode

Phenols,in stead of con venti onal alcoholic compounds,are used to in itiate ring-openi ng polymerizati on(ROP)of ethyle neoxide and propyle ne oxide in bulk at room temperature in cooperati on with the recently prevaili ng bicompone nt metal-free catalyst comprising an organobase and triethylborane.Experimental and DFT calculation results both point out that due to the lower nucleophilicity of the initiating(phe no late)species than the propagating(alcoholate)species,chai n initiat ion is distinctly slower tha n propagation and the difference becomes eve n larger as the acidity of the phe nolic in itiator increases.Nevertheless,we 11-defi ned polyethers with expected molar mass,low dispersity,and high end-group fidelity are afforded substa ntiating that the ROP is living/c on trolled in spite of the slow initiation.Evolution of product composition indicates that the reaction on alcoholates(i.e.,propagation)is effectively inhib-ited by the unreacted phenols during the initiation step because of the adequately large acidity differenee,which is key to the success of the slow-initiation living/controlled polymerization.The acidity difference betwee n phe nol and alcohol also facilitates the fulfill-ment of highly selective phenolysis of epoxides,a"1+1"type addition reaction between phenol and epoxide(in excess)rather than the"1+n"type ROP reaction,by use of a milder organobase and decreased Lewis acid/base ratio.

Frustrated Lewis Pair Catalysis: It Takes Two to Make a Thing Go Right

Since the introduction of the concept of frustrated Lewis pair by Stephan in 2006,the frustrated Lewis pair(FLP)chemistry has evolved into a rich and fruitful research area which is largely responsible for the renaissance of main group chemistry in recent years.Among many applications of FLP,design of catalytic systems based on the concept of FLP,pioneered by Stephan,Chen and others,provides a powerful arsenal that has been applied to organic synthesis and polymerization.This article will highlight key advances in the development of FLP related catalysis.

Multifunctional Gold Nanoparticles@Imidazolium-Based Cationic Covalent Triazine Frameworks for Efficient Tandem Reactions

Tandem catalytic reactions have attracted extensive interest because of their ability to reduce reaction steps,energy consumption,and waste.However,the construction of highly efficient tandem catalytic systems is still a significant challenge due to the problematic integration of multiple active sites in one reaction system and the incompatibility of different reaction conditions.Although metal nanoparticles(MNPs)supported on porous framework materials have shown excellent catalytic performances in various reactions,their cooperative catalysis for tandem reactions is rarely reported.

Chiral Bicyclic Imidazole-Catalyzed Direct Enantioselective C-Acetylation of Indolones

By adjusting the bond angle and stereocontrol substituent of the chiral bicyclic imidazole catalysts,direct enantioselective C-acetylation of indolones and their sequencial pattern have been successfully developed.Indolones bearing a quaternary stereocenter were synthesized with satisfactory yields and excellent enantioselectivities(up to 97%ee).The reaction can be realized with 410 turnover numbers,and the products can be transformed into several functional compounds via simple derivations of the acetyl group.

Ln-substituted polytungstates as efficient hetergeneous catalysts for Knoevenagel condensation reaction

Three isomorphic polytungstates,CsgK_(18)H_(10){[Sm_(2)(H_(2)O)_(4)W_(4)O_(10)(AsW_(9)0_(33))3]_(2)(N(CH_(2)PO_(3))_(2))}:46.5H_(2)O(1),CS_(10)K_(9)H_(18){[Eu_(2)(H_(2)O)_(4)W_(4)O_(10)(AsW_(9)0_(33))_(3)]_(2)(N(CH_(2)PO_(3))_(2))}.41.5H_(2)O(2),Cs_(10)K_(9)H_(18){[Gd_(2)(H_(2)O)_(4)W_(4)O_(10)(AsW_(9)O_(33))_(3)]_(2)(N(CH_(2)PO_(3))_(2))}:46H_(2)O(_(3)),have been successfully synthesized and characterized by routine methods,and demonstrated excellent catalytic activities in Knoevenagel condensation reaction as heterogeneous catalysts.Notably,catalyst 1 achieved higher reaction activity than catalysts 2 and 3,where a satisfactory reaction yield(95%)and high TON value(6380)could be obtained at moderate reaction condition.In addition,in the scale-up experiment,with the help of catalyst 1,7.8g benzaldehyde and 5.7g ethyl cyanoacetate could transform into corresponding condensation product with a satisfactory yield(83%)and impressive TON value(13.883).

A Novel Co(Ⅱ)-organic Framework with Multiple Active Sites for Selective Gas Adsorption

A novel metal-organic framework[Co(BTTA)(H_(2)O)_(2)]_(n)(FJI-H_(2)4)has been prepared from H_(2)BTTA ligand and CoCl_(2),and its structure was determined by single-crystal X-ray diffraction,thermogravimetric analysis,and Fourier transform infrared spectroscopy.It has relatively narrow pores and high density of open metal ions and free Lewis base sites.Gas adsorption tests demonstrate that FJI-H_(2)4 has moderate CO_(2)(34.0 cm^(3)·g^(–1))and C_(2)H_(2)(53.0 cm^(3)·g^(–1))adsorption capacity,but displays high selectivity of CO_(2)/N_(2)(87)and C_(2)H_(2)/CH_(4)(66)under ambient conditions(298 K,1 atm),which may be attributed to its relatively narrow pores and polar environment.This work will provide a potential strategy for preparing practical porous metal-organic frameworks for gas adsorption and purification.

Synthesis of Chiral Sulfoxides and Application in Enantioselective Allylation of Aldehydes with Allyltrichlorosilane

1 Results The enantioselective addition of allylic organometallic reagents to aldehydes is a fundamental tool in organic synthesis.The high degree of both diastereo-and enantioselectivity gives the possibility to obtain a wide series of homoallylic alcohols,versatile intermediates in a great number of synthesis[1]. One of the most successful approaches is related to the discovery that organocatalytic activation of the nucleophilic allyltrichlorosilanes by means of neutral Lewis bases,such as formamides,...

Solvent-Regulated Diastereodivergent [3+2] Annulations of CF_(3)-Containing Morita-Baylis-Hillman Carbonates with Cyclic Sulfonimines

A solvent-regulated diastereodivergent[3+2]annulation reaction between Morita-Baylis-Hillman carbonates from aryl trifluoromethyl ketones and cyclic sulfonimines is developed under the catalysis of a modified cinchona alkaloid,furnishing diverse polycyclic products bearing vicinal quaternary stereogenic centers with outstanding enantioselectivity and moderate to high diastereoselectivity.

Efficient Synthesis of P-Chirogenic Compounds Enabled by Chiral Selenide-Catalyzed Enantioselective Electrophilic Aromatic Halogenation

P-chirogenic compounds have been applied in different fields,especially in asymmetric catalysis as ligands and organocatalysts.However,broader applicability has been severely restricted by the lack of efficient synthetic methods.Consequently,developing efficient methods to access these compounds is of high synthetic value.Herein,we report a convenient,efficient,and unprecedented pathway to construct valuable P-chirogenic compounds via chiral selenide-catalyzed enantioselective electrophilic aromatic halogenation.Using a new chiral bifunctional selenide as the catalyst,a variety of bis(2-hydroxyaryl)aryl phosphine oxides were efficiently converted to the corresponding chlorinated and brominated P-chirogenic compounds with good to excellent enantioselectivities.By slightly adjusting the catalyst and solvent,this method is also able to prepare chiral alkyl diaryl phosphine oxides and diaryl phosphinates.Furthermore,control experiments revealed the decomposition pathways of catalysts and the possible reasons why chiral selenide catalyst was more effective than chiral sulfide catalyst.The effect of hydrogen bonding was studied,and the reason why the chlorination took place on the various aromatic rings was elucidated when the substrates were switched from triaryl phosphine oxides to alkyl diaryl phosphine oxides and diaryl phosphinates.

Vertically aligned γ-Al00H nanosheets on Al foils as flexible and reusable substrates for NH3 adsorption

Vertically aligned γ-AlOOH nanosheets （NSs） have been successfully fabricated on flexible Al foils via a solvothermal route without morphology-directing agents. Three different reaction temperature （25, 80, and 120 ℃） and time （30 min, 45 min, and 24 h） are discussed for the growth period, which efficiently tune the density and size of theγ-AlOOH NSs. Meanwhile, the growth speed of the nanosheets confirms that dominant growth stage is seen in the initial 45 min. Furthermore, the interlayer of the γ-AlOOH NSs displays an average height of 140 nm and superhydrophilicity. By dynamic adsorption, the as- synthesized γ-AlOOH NSs exhibit an outstanding NH3 adsorption capacity of up to 146 mg/g and stably excellent regeneration for 5 cycles. The mechanism of NH3 adsorption on the in-plane of the γ-AlOOH NSs is explained by the Lewis acid/base theory. The H-bond interactions among the NH3 molecules and the edge groups （-OH） further improve the capture ability of the nanosheets.

Enhanced Catalysis of Pt_(3) Clusters Supported on Graphene for N–H Bond Dissociation

We report an in-depth study of catalytic N–H bond dissociation with typical platinum clusters on gra-phene supports.Among all the pristine graphene-and defective graphene-supported Pt clusters of different sizes that were studied,the Pt_(3)/G cluster possesses the highest reactivity and lowest activa-tion barriers for each step of N–H dissociation in the decomposition of ammonia.