An Efficient Synthesis of 2-Substituted Benzoxazoles via RuCl3.3H2O Catalyzed Tandem Reactions in Ionic Liquid

An efficient synthesis of 2-substituted benzoxazoles through RuCl3·3H2O catalyzed, air oxidized tandem reactions of 2-aminophenols and aldehydes in [bmim]BF4 was developed. This synthetic strategy has such advantages as mild reaction conditions, cost-free oxidant, readily available starting materials, and recyclable catalyst and solvent. As an application, it was successfully used in the synthesis of the unreported 5-（benzoxazol-2-yl）-2＇-deoxyuridines with potential biological activities.

Ring strain strategy for the control of regioselectivity. Goldcatalyzed anti-Markovnikov cycloisomerization initiated tandem reactions of alkynes

Gold-catalyzed nucleophilic addition to terminal alkynes has received considerable interest in the past decade, as this chemistry offers a highly efficient and regioselective way for CAC, CAH and CAX bond formation. However, such a nucleophilic addition mainly involves a Markovnikov addition. In this short review, the recent progress of the gold-catalyzed 5-endo-dig cycloisomerization-initiated tandem reactions by utilizing the steric strain in ring formation to achieve an anti-Markovnikov regioselectivity was reviewed, including the scope of reactions, mechanism and synthetic applications.

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.

An Efficient Synthesis of Spiroquinoxalinones via Tandem Reactions

A mild and efficient synthesis of spiroquinoxalinones via tandem condensation of chlorooxoindoline 1 with benzene-1,2-diamines 2 is described.And a plausible mechanism for the reaction is proposed.

Visible light induced tandem reactions:An efficient one pot strategy for constructing quinazolinones using in-situ formed aldehydes under photocatalyst-free and room-temperature conditions

A facile tandem route has been developed for constructing quinazolinones from various aminobenzamides and in-situ generated aldehydes.Visible light was found to play a dual role:first oxidizes the alcohol to the aldehyde and then facilitates its cyclization with o-substituted aniline.Furthermore,alcohols are perfe ct alternatives to aldehydes because they are greene r,more available,more economical,more stable,and less toxic tha n aldehydes.The first reaction step continuously provides material for the second step,which effectively reduces loss through volatilization,oxidation,and polymerization of the aldehyde,while avoiding its toxicity.A variety of quinazolinones can be prepared in the presence of visible light without any additional photocatalyst.The developed synthesis protocol proceeds with the merits of mild conditions,broad substrate scope,operational simplicity,a nd high atom efficiency,with an eco-energy source under metal-free,photocatalyst-free,and ambient conditions.

Novel Tandem Three Consecutive Reactions: Aza-Wittig, Imine Condensation and Electrophilic Aromatic Substitution Strategy to Indolizine Synthesis

Reaction of ethyl (Z)-3-(heteroaryl/aryl)-2-((triphenyl-λ5-phosphaneylidene) amino) acrylates intermediates with 2,3-thiophenedicarboxaldehyde was used in novel Tandem three consecutive reactions: aza-Wittig, imine condensation and electrophilic heteroaromatic cyclization to obtain a series of indolizines. A tentative mechanism of this reaction is proposed.

Extrapolation of the gold-catalyzed cycloisomerization to the palladium-catalyzed cross-coupling/cycloisomerization of acetylenic alcohols for the synthesis of polysubstituted furans:Scope and application to tandem processes

This paper describes the development of an integrated approach for the preparation of diverse furan derivatives from acetylenic alcohols by gold and palladium catalyzed π-activation chemistry.Notably,this new method was found to be amenable to cyclooctyl-containing substrates,which represents a significant extension to this methodology compared with our previous reports.Furthermore,this newly developed method allowed for the direct construction of cyclooctyl furans from their synthetic precursors under Sonogashira conditions.Experimental results revealed that palladium played two major functions in these reactions,including（1） an essential catalyst in the cross-coupling reaction of the substrates;and（2）facilitating the cyclization of the acetylenic alcohol intermediates through a typical π-activation process.The scope of this chemistry was highlighted by the one-pot synthesis of 3-iodofuran,which provided an opportunity for further functionalization（via coupling methods）.Finally,the AuBr3 protocol was also elaborated to domino cyclization/C-H activation reactions,as well as the cyclization of acyclic precursors.Taken together,the results of this study demonstrate that gold and palladium catalysts can be used to complement each other in cyclization reactions.

Ultrasound assisted multicomponent reactions:A green method for the synthesis of N-substituted 1,8-dioxo-decahydroacridines usingβ-cyclodextrin as a supramolecular reusable catalyst in water

We demonstrate a superficial method for the synthesis of N-substituted 1,8-dioxo-decahydroacridines using β-cyclodextrin as a supramolecular,biodegradable,and reusable catalyst in aqueous medium.The reaction product is in excellent yield with moderate to excellent selectivity.The mechanistic transformation presumably proceeds via a one-pot,multicomponent cyclization of dimedone in the presence of aromatic aldehydes and aromatic amines/INH,undergoing a tandem Michael addition reaction.The proposed approach in this study provides a highly efficient and environmentally benign route to N-substituted 1,8-dioxo-decahydroacridines.

Efficient Synthesis of Complex Bridged 1,3-Oxazabicycles via Reactions of N-Alkyl-1,10-phenanthrolinium Halides with Cyclic 1,3-Diketones

Complex bridged 1,3-oxazabicycles and 1,4-disubstituted 1,10-phenanthroline derivatives were efficiently prepared by the reactions of N-methyl or N-benzylphenanthrolinium halides with cyclic 1,3-dicarbonyl compounds in a K2CO3/CH3CN system.

Synthesis of Spiro Dihydrofurans and 1,8-Dioxo-xanthenes via DABCO Catalyzed Tandem Reaction of Aldehyde with Cyclohexane-1,3-dione and Dimedone

The 1,4-diazabicyclo[2.2.2]octane（DABCO） catalyzed reaction of cyclohexane-1,3-dione or dimedone with various aldehydes in acetonitrile resulted in the polysubstituted tetraketones, spiro dihydrofurans or 1,8-dioxo-xanthenes derivatives as main products respectively according to the structure of reactants and reaction conditions.

SYNTHESIS OF A POTENTIAL ANTIFEEDANT SESOUITERPENE INTERMEDIATE FROM A NEW TERPENOID A, B-RING SYNTHON BY TANDEM NICHAEL REACTION

An efficient synthesis of functionalized 6-decalone 16, starting from a dienolate anion 3a via a tandem Michael reaction, is described. 16 could be used as a potential intermediate for synthesis of drimane related sesquiterpenes.

Metal-Free Synthesis of 2-Aminobenzothiazoles via I2-Catalyzed Tandem Cyclization Reaction of Amines and Carbon Disulfide

Comprehensive Summary,A convenient approach for the construction of 2-aminobenzothiazoles via I2-catalyzed tandem cyclization reaction of amines and carbon disulfide has been developed.The present approach starts from simple and readily available starting materials,affording a series of 2-aminobenzothiazoles in up to 89%yields under metal-free conditions.In this work,C—H/N—H functionalization was achieved and multiple C-hetero bonds were successfully constructed in one pot.

A H_(4)SiW_(12)O_(40)-catalyzed three-component tandem reaction for the synthesis of 3,3-disubstituted isoindolinones

A H_(4)SiW_(12)O_(40)-catalyzed three-component tandem reaction of 2-acylbenzoic acids,primary amines and phosphine oxides to form 3,3-disubstituted isoindolinones was developed.By employing A H_(4)SiW_(12)O_(40)as the catalyst and dimethyl carbonate(DMC)as the solvent,a diverse range of 2-acylbenzoic acid derivatives and primary amines worked well to give the C3-phosphinoyl-functionalized 3,3-disubstituted isoindolinones with the yield range of 61%-87%.Advantages of this transformation include green catalyst and solvent,available starting materials,broad substrate scope,high efficiency and operational simplicity with water as the sole by-product.The strategy achieved an efficient and green molecular fragment assembly to access isoindolinones,which would provide opportunities for the synthesis of potential biologically active molecules in a green manner.

Mesoporous Fe-Doped Carbon Electrocatalysts with Highly Exposed Active Sites for Efficient Synthesis of Hydrogen Peroxide and Tandem Epoxidation of Propene

Catalytic tandem synthesis of fine chemicals using the in situ-formed intermediates by electrocatalytic reactions has increasingly attracted attention in recent years.The difficulty lies in the low local concentration of intermediates because of the slow formation rates in the catalytically electrochemical process.We showcase an efficient tandem epoxidation of propene,which is accelerated by the in situ-generated hydrogen peroxide(H_(2)O_(2)).The catalysts of iron-doped tubular mesoporous carbons feature ultrathin carbon walls and record-high exposed external surface areas,which enable a H_(2)O_(2) formation rate of 747.7 mmol gcat^(-1) h^(-1) at 0.4 V versus reversible hydrogen electrode,together with a H_(2)O_(2) Faradaic efficiency of nearly 100%.A positive correlation between the exposed external surface area and the oxygen reduction activity is experimentally observed.By utilizing the in situ-generated H_(2)O_(2),the tandem epoxidation of propylene displays a yield rate of 80.3μmol gTS-1^(-1) h^(-1) for propylene oxide.The high performance originates from the high local concentration of H_(2)O_(2) surrounding the titanium silicalite-1 catalysts for propylene epoxidation.The results may inspire other tandem electrochemical reactions by using the mesoporous catalysts for synthesis of building block chemicals.

Tandem Functionalization-Carboxylation Reactions ofπ-Systems with CO_(2)

The tandem catalytic functionalization/carboxylation of double as well as triple carbon-carbon bonds with CO_(2) represent an emerging research area in synthetic organic methodology.In particular,the combination of mild reaction conditions,stoichiometric acceptor/donorless conditions(visible light photoredox catalysis)and chiral catalysts contributed to a rapid development of this intriguing research area capable of creating chemical diversity/complexity from readily available unsaturated hydrocarbons and CO2 as a C1-buinding block.The most recent developments in the field have been collected in the present review article and organized,based on the different sets ofπ-systems/intermediates/reactive partners employed(i.e.,nickelalactones,organo-halides)as well as synthetic strategies(i.e.,visible-light photo redox catalysis).

Tandem nanocatalyst design: putting two step-reaction sites into one location towards enhanced hydrogen transfer reactions

Efficient tandem reactions on a single catalytic nanostructure would be beneficial to improving chemical transformation efficiency and reducing safety implications. It is imperative to identify the active sites for each single step reaction so that the entire reaction process can be optimized by designing and integrating the sites. Herein, hydrogen transfer reaction is taken as a proof-of-concept demonstration to show that the spatial integration of active sites is important to the catalytic efficiency of the entire process in tandem reactions. We identified specific active sites (i.e., various sites at faces versus corners and edges) for formic acid decomposition and alkene/nitrobenzene hydrogenation-the two steps in hydrogen transfer reactions, by employing three different shapes of Pd nanocrystals in tunable sizes. The investigation reveals that the decomposition of formic acid occurs preferentially at the edge sites of cubic nanocrystal and the plane sites of octahedral/ tetrahedral nanocrystals, while the hydrogenation takes place mainly at the edge sites of both cubic and octahedral/ tetrahedral nanocrystals. The consistency of active edge sites during different step reactions enables cubic nanocrystals to exhibit a higher activity than octahedral nanocrystals in hydrogen transfer reactions, although octahedrons offer comparable activities to cubes in formic acid decomposition and hydrogenation reactions. Guided by these findings, we further improved the overall performance of tandem catalysis by specifically promoting the limiting step through nanocatalyst design. This work provides insights into the rational design of heterogeneous nanocatalysts in tandem reactions.

Synthesis and Crystal Structure of a Novel 14,20-Annulated Pentacyclic Steroid 17(S)-Methyl-13β-hydroxyl-14(R),20(S)-epoxy-pregn-4-en-3-one

The title compound 17（S）-methyl-13β-hydroxyl-14（R）,20（S）-epoxy-pregn-4-en-3-one was synthesized by an improved tandem reaction, and its structure was determined by IR, NMR, HR MS and X-ray single-crystal diffraction. The crystal belongs to orthorhombic, space group P212121 with a = 10.55248（15）, b = 12.14700（16）, c = 14.56841（18） ？, V = 1867.39（4） ？3, Z = 4, Dc= 1.175 g/cm3, μ= 0.604 mm-1, F（000） = 720, the final R = 0.0400 and w R = 0.1072 for 3610 observed reflections with I 〉 2σ（I）.

Total Synthesis of UCS1025A via Tandem Carbonylative Stille Cross Coupling and Diels-Alder Reactiont

We report an efficient and convergent strategy for the total synthesis of UCS1025A and its diastereomer tetra-epi-UCS1025A.Ucs1025A is a representative member of the naturally occurring pyrrolizidinone polyketides,from which members with potent antibacterial,antifungal,and anticancer activities have been identified.Our approach features a tandem carbonylative Stille cross coupling and Diels-Alder reaction to forge a key C-C bond and build the trans-decalin system.This tandem process utilizes carbon monoxide as a one-carbon linchpin to stitch a vinyl triflate and a vinylstannane together and form the desired enone moiety for the subsequent intramolecular Diels-Alder cyclization.Our synthesis also provides a versatile approach for the synthesis of other related pyrrolizidinone-containing polyketides.

Efficient approach to thiazolidinones via a one-pot three-component reaction involving 2-amino-1-phenylethanone hydrochloride,aldehyde and mercaptoacetic acid

A highly efficient three-component reaction has been developed for the synthesis of thiazolidinones involving the reaction of 2-amino-l-phenylethanone hydrochloride with an aromatic aldehyde and mercaptoacetic acid in the presence of diisopropylethylamine in a single pot.Critically,this reaction exhibited excellent chemoselectivity,with the nitrogen atom of the 2-amino-l-phenylethanone component reacting selectively with the aromatic aldehyde to give the corresponding Schiff base.Nucleophilic attack at the carbon of the Schiff base by the sulfur atom of mercaptoacetic,followed by a cyclocondensation reaction between the nitrogen and the carboxylic acid moiety afforded the desired thiazolidinones,which were fully characterized by spectroscopic techniques.

Synthesis and Crystal Structure of 1-(2,6-Dichloro-4-nitrophenyl)-5-amino-4-cyanopyrazole

The crystal structure of 1-（2,6-dichloro-4-nitrophenyl）-5-amino-4-cyanopyrazole （C10H10Cl2N5O2, Mr = 298.09） has been determined by single-crystal X-ray diffraction. It crystallizes in the triclinic system, space group P1^- with a = 8.1258（10）, b = 8.6460（10）, c = 10.0214（12） A, α = 68.986（2）, β = 71.598（2）, γ = 85.181（2）°, V = 623.26（13） A3, Z = 2, Dc = 1.588 g/cm^3,μ = 0.525 mm^-1, F（000） = 300, R = 0.0613 and wR = 0.1524 for 1890 observed reflections, and the extinction coefficient = 0.010（5）. The crystal structure is stabilized by N-H...N hydrogen bonds.