Asymmetric multicomponent reactions (AMCRs): the new frontier

Asymmetric organocatalytic multicomponent reactions for efficient construction of bicyclic compounds bearing bisacetal and isoxazolidine moieties

An organocatalytic multicomponent reaction of N-protected hydroxylamines, acrylaldehyde and acetal-containing enones was developed. Bisacetal-containing bicyclic isoxazolidine derivatives bearing four continuous stereocenters were formed with excellent stereoselectivities. A plausible reaction pathway was proposed based on ¹⁸O-labeling control experiments.

Novel biocompatible core/shell Fe3O4@NFC@Co(ii) as a new catalyst in a multicomponent reaction: an efficient and sustainable methodology and novel reusable material for one-pot synthesis of 4H-pyran and pyranopyrazole in aqueous media

Today, due to the developing need for inexpensive catalysts, recyclable magnetic nanocatalysts immobilized on polysaccharides possess many advantages over classical heterogeneous catalysts. However, cellulose has been an appealing material in catalysis science and technology. In this work, by controlling the interaction between the inorganic complexes and the support material, we designed a high activity nanostructured combination of a magnetic nanoparticle Fe3O4@NFC@Co(ii) terminated complex as a multi-nuclear catalyst. This protocol involves an environment friendly approach using cobalt acetate. The magnetic nanostructure Fe3O4@NFC@Co(ii) can be used as a novel, green, and a powerful catalyst that demonstrates a short reaction time, high yield and easy procedure for the cascade Knoevenagel-Michael-cyclocondensation reaction for the one-pot synthesis of 4H-pyrans and pyranopyrazoles. The superparamagnetic nanocomposite could be conveniently separated by using an external magnet. Moreover, the catalyst could be reused at least five times in new reaction runs without a noticeable loss of activity. The prepared catalyst was characterized by FT-IR, XRD, VSM, FESEM, EDAX, TEM, ICP, and TGA techniques. The experiments were achieved with good yields and implied that the catalytic method was effective and convenient for heterocyclic synthesis.

Tandem Prins cyclizations for the construction of oxygen containing heterocycles

Tandem Prins cyclization is a versatile method for the synthesis of fused/bridged/spirotetrahydropyran scaffolds. Therefore, it has become a powerful tool for the stereoselective synthesis of oxygen/nitrogen containing heterocycles. Indeed, previous review articles on Prins spirocyclization illustrate the synthesis of spirotetrahydropyran derivatives and the aza-Prins reaction demonstrates its application in the total synthesis of natural products. The current review is devoted specifically to highlight tandem Prins cyclizations for the construction of fused scaffolds and related frameworks with a particular emphasis on recent applications. The mechanistic aspects and the scope of the methods are briefly discussed herein.

Chemodivergent reactions

An important strategy for the efficient generation of diversity in molecular structures is the utilization of common starting materials in chemodivergent transformations. The most studied solutions for switching the chemoselectivity rely on the catalyst, ligand, additive, solvent, temperature, time, pressure, pH and even small modifications in the substrate. In this review article several processes have been selected such as inter- and intramolecular cyclizations, including carba-, oxa-, thia- and oxazacyclizations promoted mainly by Brønsted or Lewis acids, transition metals and organocatalysts, as well as radical reactions. Catalyst-controlled intra- and intermolecular cyclizations are mainly described to give five- and six-membered rings. Cycloaddition reactions involving (2+2), (3+2), (3+3), (4+1), (4+2), (5+2), (6+2) and (7+2) processes are useful reactions for the synthesis of cyclic systems using organocatalysts, metal catalysts and Lewis acid-controlled processes. Addition reactions mainly of carba- and heteronucleophiles to unsaturated conjugated substrates can give different adducts via metal catalyst-, Lewis acid- and solvent-dependent processes. Carbonylation reactions of amines and phenols are carried out via ligand-controlled transition metal-catalyzed multicomponent processes. Ring-opening reactions starting mainly from cyclopropanols, cyclopropenols and epoxides or aziridines are applied to the synthesis of acyclic versus cyclic products under catalyst-control mainly by Lewis acids. Chemodivergent reduction reactions are performed using dissolving metals, sodium borohydride or hydrogen transfer conditions under solvent control. Oxidation reactions include molecular oxygen under solvent control or using different dioxiranes, as well as chemodivergent palladium catalyzed cross-coupling reactions using boronic acids are applied to aromatic and allenic compounds. Other chemodivergent reactions such as alkylations and allylations under transition metal catalysis, dimerization of acetylenes, bromination of benzylic substrates, and A³-couplings are performed via catalyst- or reaction condition-dependent processes.

Catalytic Asymmetric Three-component Hydroacyloxylation/ 1,4-Conjugate Addition of Ynamides

A highly enantioselective three-component hydroacyloxylation/1,4-conjugate addition of ortho-hydroxybenzyl alcohols, ynamides and carboxylic acids was developed under mild reaction conditions in the presence of a chiral N,N'-dioxide/Sc(OTf)₃ complex, which went through in situ generated ortho-quinone methides with α-acyloxyenamides, delivering a range of corresponding chiral α-acyloxyenamides derivatives containing gem(1,1)-diaryl skeletons in moderate to good yields with excellent ee values. The scale-up experiment and further derivation showed the practicality of this catalytic system. In addition, a possible catalytic cycle and transition state model was proposed to elucidate the origin of the stereoselectivity based on X-ray crystal structure of the α-acyloxyenamide intermediate and product.

Copper(I)-Catalyzed Ketenimine Formation/Aza-Claisen Rearrangement Cascade for Stereoselective Synthesis of α-Allylic Amidines

A copper-catalyzed three-component reaction of terminal alkynes, TsN₃, and tertiary allylic amines is developed toward the one-pot synthesis of α-allylic amidines. The product was synthesized on gram scale under 1 mol % of catalyst loading. Transformations of products into alkenyl amine and other nitrogen-containing compounds are demonstrated without any loss of stereochemical information.

Utilization of 1-phenylimidazo[1,5-a]quinoline as partner in 1,4-dipolar cycloaddition reactions

A Selected set of 2-(quinolin-2-yl)-1,3-oxazepino[7,6-b]indoles 4a–d and dihydroacenaphtho[1,2-f][1,3]oxazepine 5 have been prepared via 1,4-dipolar cycloaddition reaction involving 1-phenylimidazo[1,5-a]quinoline, dimethyl acetylenedicarboxylate, and N-(substituted)isatins or acenaphthoquinone. Structures of the new heterocycles 4a–d and 5 are supported by NMR and HRMS spectral data, and confirmed by single-crystal X-ray crystallography for 4c and 5.

Solvent-free synthesis of isoindolo[2,1-c]pyrazolo[1,5-a]quinazoline and pyrazolo[5',1':2,3]pyrimido[6,1-a]isoindol derivatives through a one-pot three-component reaction

Some 5-substituted 3-aminopyrazoles were used for the synthesis of isoindolo[2,1-c]pyrazolo[1,5-a]quinazoline and pyrazolo[5',1':2,3]pyrimido[6,1-a]isoindol derivatives via a mild and efficient one-pot three-component reaction with 2-formylbenzoic acid and different CH-acids under solvent-free condition.

Sulfonic Acid-Functionalized Magnetic Nanoparticles as an Efficient Catalyst for the Synthesis of Benzo[4, 5]imidazo[1, 2-a]pyrimidine Derivatives, 2-Aminobenzothia Zolomethylnaphthols and 1-Amidoalkyl-2-naphthols

BACKGROUND

Carbon-based sulfonated catalysts have several advantages but their separation by filtration is still a challenge. On the other hand, the synthesis of magnetic sulfonated carbon nanoparticle indicated that the magnetic separation could be an efficient way to separate the catalyst from the reaction mixture.

OBJECTIVE

In order to synthesize a separable magnetic Fe3O4@C-SO3H nanoparticle (MNPs) with high catalytic activity in organic transformation, three environmental-benign and low-cost sulfonic acidfunctionalized magnetic nanoparticle (Fe3O4@C-SO3H) were successfully synthesized.

MATERIALS AND METHODS

The Nano catalysts were prepared by solvothermal carbonization of Sucrose (Suc), Starch (Sta) or Cellulose (Cel) in the presence of Fe3O4 Nanoparticle and then grafting of the sulfonic groups on the surface of resulted Fe3O4@C nanoparticles in the presence of p-Toluenesulfonic. Then the Nano catalysts were characterized using XRD, FESEM and FT-IR.

RESULTS

Three Fe3O4@C-SO3H were successfully synthesized. The resulted MNPs were used for the synthesis of benzo [4, 5] imidazo[1, 2-a]-pyrimidine derivatives, 2/-aminobenzothiazolomethylnaphthols and 1-amidoalkyl-2-naphthols under solvent-free conditions in excellent yields. It was found that high catalytic activity and easy magnetic separation from the reaction mixture are important achievement with regard to the efficiency and reusability of the catalyst in synthesis.

CONCLUSION

The MNPs were synthesized and used as an efficient catalysts for the one-pot synthesis of benzo [4, 5] imidazo[1, 2-a]-pyrimidine derivatives, 2/-aminobenzothiazolomethylnaphthols, and 1-amidoalkyl-2- naphthols under solvent-free conditions in excellent yields. High catalytic activity and easy magnetic separation from the reaction mixture are two factors for evaluating the performance of Fe3O4@C-SO3H nanoparticles in the organic transformations.

Recent advances in catalytic enantioselective multicomponent reactions

Multicomponent reactions (MCRs) undoubtedly correspond to one of the synthetic strategies that best fit the new demands of chemistry for presenting high atom economy and enabling molecular diversity. However, many challenges still exist when products possessing stereogenic centres are formed. The field of asymmetric catalytic reactions has achieved significant progress in recent decades; new applications for chiral ligands and catalysts have been demonstrated and new catalysts have been specifically designed for challenging chemical conversions. In this sense, highly efficient approaches for classic multicomponent reactions such as the Ugi reaction and a number of new asymmetric MCRs have been described. In this review we discuss the recent developments that enable catalytic enantioselective MCRs including the proposed mechanistic pathways.

Recent applications of thiourea-based organocatalysts in asymmetric multicomponent reactions (AMCRs)

This review describes the recent applications of thiourea-based organocatalysts in asymmetric multicomponent reactions.

Copper-catalyzed tandem phosphorylative allenylation/cyclization of 1-(o-aminophenyl)prop-2-ynols with the P(O)–H species: access to C2-phosphorylmethylindoles

A novel method to synthesize C2-phosphorylmethylindoles via the carbocation formation initiated tandem phosphorylative allenylation/cyclization of 1-(o-aminophenyl)prop-2-ynols with the P(O)–H species has been developed.

Predicting reactive sites with quantum chemical topology: carbonyl additions in multicomponent reactions

The reactivity of an atom within a molecule depends mostly on the way the electron density polarizes reflected in the quadrupole moment of the reactive atom.

An asymmetric hydrocyanation/Michael reaction of α-diazoacetates via Cu(i)/chiral guanidine catalysis

An asymmetric one-pot hydrocyanation/Michael reaction of α-aryl diazoacetates with trimethylsilyl cyanide, tert-butanol, and N-phenylmaleimides has been realized using a chiral guanidinium salt/CuBr catalyst.

Recent advances in alkaline earth metal-enabled syntheses of heterocyclic compounds

This review summarizes recent progress in alkaline earth metal enabled syntheses of heterocyclic compounds.

Experimental and DFT mechanistic insights into one-pot synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-diones under catalysis of DBU-based ionic liquids

Kinetic impacts of two DBU-based ionic liquids in the three-component synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-diones and the mechanism of the reaction were investigated by DFT calculations.

Sequential multicomponent catalytic synthesis of pyrrole-3-carboxaldehydes: evaluation of antibacterial and antifungal activities along with docking studies

A sequential multicomponent method is developed to access highly substituted N-arylpyrrole-3-carbaldehydes and tested for antibacterial and antifungal activities against bacterial strains.