Synthesis of Dihydroquinoxalinones from Biomass-Derived Keto Acids and o-Phenylenediamines

A novel catalyst-free cascade amination/cyclization/reduction reaction was developed for the synthesis of various Dihydroquinoxalinones under mild conditions from accessible biomass-derived keto acids and 1,2-phenylenediamines with ammonia borane as a hydrogen donor. This single-step approach enables a simple and eco-friendly route toward the direct synthesis of 12 kinds of Dihydroquinoxalinones in moderate to excellent yields in the green solvent dimethyl carbonate. The results of deuterium-labeling experiments and density function calculations demonstrate that the reductive process proceeds along a double hydrogen transfer pathway. An acceptable yield of Dihydroquinoxalinone can be afforded in a gram-scale experiment, illustrating the practicality of the as-reported reaction system.

Sulfonamides with Heterocyclic Periphery as Antiviral Agents

Sulfonamides are the basic motifs for a whole generation of drugs from a large group of antibiotics. Currently, research in the field of the new sulfonamide synthesis has received a "second wind", due to the increase in the synthetic capabilities of organic chemistry and the study of their medical and biological properties of a wide spectrum of biological activity. New reagents and new reactions make it possible to significantly increase the number of compounds with a sulfonamide fragment in combination with other important pharmacophore groups, such as, for example, a wide class of N-containing heterocycles. The result of these synthetic possibilities is the extension of the activity spectrum-along with antibacterial activity, many of them exhibit other types of biological activity. Antiviral activity is also observed in a wide range of sulfonamide derivatives. This review provides examples of the synthesis of sulfonamide compounds with antiviral properties that can be used to develop drugs against coxsackievirus B, enteroviruses, encephalomyocarditis viruses, adenoviruses, human parainfluenza viruses, Ebola virus, Marburg virus, SARS-CoV-2, HIV and others. Since over the past three years, viral infections have become a special problem for public health throughout the world, the development of new broad-spectrum antiviral drugs is an extremely important task for synthetic organic and medicinal chemistry. Sulfonamides can be both sources of nitrogen for building a nitrogen-containing heterocyclic core and the side chain substituents of a biologically active substance. The formation of the sulfonamide group is often achieved by the reaction of the N-nucleophilic center in the substrate molecule with the corresponding sulfonylchloride. Another approach involves the use of sulfonamides as the reagents for building a nitrogen-containing framework.

Novel O-acylated amidoximes and substituted 1,2,4-oxadiazoles synthesised from (+)-ketopinic acid possessing potent virus-inhibiting activity against phylogenetically distinct influenza A viruses

This article describes the synthesis and antiviral activity evaluation of new substituted 1,2,4-oxadiazoles containing a bicyclic substituent at position 5 of the heterocycle and O-acylated amidoximes as precursors for their synthesis. New compounds were obtained from the (+)-camphor derivative (+)-ketopinic acid. The chemical library was tested in vitro for cytotoxicity against the MDCK cell line and for antiviral activity against influenza viruses of H1N1 and H7N9 subtypes. The synthesised compounds exhibited high virus-inhibiting activity against the H1N1 influenza virus. Some synthesised compounds were also active against the influenza virus of a different antigenic subtype: H7N9. The mechanism of the virus-inhibiting activity of these compounds is based on their interference with the fusion activity of viral hemagglutinin (HA). No interference with the receptor-binding activity of HA has been demonstrated. According to molecular docking results, the selective antiviral activity of O-acylated amidoximes and 1,2,4-oxadiazoles is associated with their structural features. O-Acylated amidoximes are likely more complementary to the binding site located at the site of the fusion peptide, and 1,2,4-oxadiazoles are more complimentary to the site located at the site of proteolysis. Significant differences in the amino acid residues of the binding sites of HA's of different types allow us to explain the selective antiviral activity of the compounds under study.

Rhodium(III)-Catalyzed Sequential C-H Activation and Cyclization from N-Methoxyarylamides and 3-Diazooxindoles for the Synthesis of Isochromenoindolones

An efficient synthetic method for structurally various isochromenoindolones has been demonstrated through Rh(III)-catalyzed C-H activation followed by a cyclization reaction of N-methoxyarylamides with 3-diazooxindoles. The sequential reaction involves the streamlined formation of C-C and C-O bonds in one pot. The present method provides a broad range of isochromenoindolones as a new privileged scaffold in moderate to good yields with the release of methoxyamine and molecular nitrogen and has the benefits of a broad substrate scope and good functional group tolerance.

Iron catalyzed β-C(sp2)–H alkylation of enamides

An attractive and cheap alternative approach was developed for the β-C(sp2)–H (fluoro)alkylation of a range of cyclic and acyclic non-aromatic enamides using either FeCl2 as a catalyst or a stoichiometric amount of nontoxic iron powder.

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

In this review we present relevant and recent applications of porphyrin derivatives as photocatalysts in organic synthesis, involving both single electron transfer (SET) and energy transfer (ET) mechanistic approaches. We demonstrate that these highly conjugated photosensitizers show increasing potential in photocatalysis since they combine both photo- and electrochemical properties which can substitute available metalloorganic photocatalysts. Batch and continuous-flow approaches are presented highlighting the relevance of enabling technologies for the renewal of porphyrin applications in photocatalysis. Finally, the reaction scale in which the methodologies were developed are highlighted since this is an important parameter in the authors' opinion.

Graphene oxide: a green oxidant-acid bifunctional carbon material for the synthesis of functionalized isoindolin-1-ones via formal amide insertion and substitution

A formal amide insertion and substitution reaction using graphene oxide as an oxidant-acid bifunctional carbon material

A new biologically active molecular scaffold: crystal structure of 7-(3-hydroxyphenyl)-4-methyl-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole and selective antiproliferative activity of three isomeric triazolo–triazoles

A study of three isomeric compounds containing a phenolic moiety attached to the nitrogen-rich triazolo–triazole bicycle is presented. In the three isomers, the phenolic OH group is in the ortho, meta and para positions. The crystal structure analysis of the meta isomer (C10H9N5O) shows that the 2H-tautomer is present in the crystal and that the molecule adopts a substantially planar geometry. However, the conformation found in the crystal is different compared to the monoprotonated cation of the same compound previously investigated in several salts. The packing of the meta isomer is driven by the formation of strong hydrogen bonds and shows the formation of infinite planar ribbons, parallel to a, formed around 21 crystallographic axes. The three isomers were tested against some cancer cell lines and also against normal cell lines. The ortho isomer shows a weak antiproliferative activity, the meta isomer shows significant antiproliferative activity against some cancer lines and no activity against healthy cell lines, and the para isomer is active against all the tested cell lines.

Tin Powder-Promoted Cascade Condensation/Allylation/Lactamization: Synthesis of Isoindolinones and Pyrazoloisoindol-8-ones

An efficient tin powder-promoted cascade condensation/allylation/lactamization of 2-formylbenzoic acids, hydrazides, and allyl bromides was developed for the synthesis of isoindolinones in good to excellent yields under mild conditions without any other additives or catalysts. Further manipulation of isoindolinones by iodocyclization process afforded the tricyclic tetrahydro-8 H-pyrazolo[5,1- a]isoindol-8-one derivatives, which could be converted into more complicated tetracyclic tetrahydro-4 H-azirino[1',2':2,3]pyrazolo[5,1- a]isoindol-4-ones.

One-Pot NBS-Promoted Synthesis of Imidazoles and Thiazoles from Ethylarenes in Water

A facile and eco-friendly method has been developed for the synthesis of imidazoles and thiazoles from ethylarenes in water. The reaction proceeds via in situ formation of α-bromoketone using NBS as a bromine source as well as an oxidant, followed by trapping with suitable nucleophiles to provide the corresponding products in good yields under metal-free conditions.

Intermolecular, redox-neutral azidoarylation of alkenes via photoredox catalysis

An intermolecular, redox-neutral azidoarylation of alkenes with pyridines and TMSN₃ has been reported via visible light-induced photoredox catalysis.

A Simple Procedure for the Synthesis of β-Hydroxyallenamides via Homoallenylation of Aldehydes

A simple one-pot synthesis of β-hydroxyallenamides is reported. This procedure entails chemo- and regioselective hydroboration of 3-en-1-ynyl-sulfonylamides with Cy₂BH followed by homoallenylation of aldehydes to yield β-hydroxyallenamides (up to 94% yield and >20:1 dr). Controlled synthesis of up to three continuous stereochemical elements was realized. Density functional theory (DFT) calculations suggest a concerted Zimmerman-Traxler chair-like transition state. Initial results suggest that enantio- and diastereoselective synthesis of β-hydroxyallenamides with optically active hydroboration reagents is viable.

O-Substituted hydroxyl amine reagents: an overview of recent synthetic advances

Reagents derived from oxygen-substituted hydroxylamine facilitate stereo- and regioselective C–N, N–N, O–N, and S–N bond-formation reactions and intra-molecular cyclizations without any expensive metal catalysts. These remarkable transformations are discussed in this review.

Thiyl radical-mediated cyclization of ω-alkynyl O-tert-butyldiphenylsilyloximes

Treatment of ω-alkynyl O-tert-butyldiphenylsilyloximes with odorless thiol and AIBN gave cyclic O-silylhydroxylamines via a radical process in good yields.

Asymmetric Michael Addition Induced by (R)-tert-Butanesulfinamide and Syntheses of Chiral Pyrazolidinone Derivatives

A highly diastereoselective Michael addition of (R)-N-tert-butanesulfinyl imidates 8 to α,β-unsaturated pyrazolidinone 3a has been developed to afford pyrazolidinones 10 possessing three contiguous stereocenters with good to excellent yield and excellent diastereoselectivity. A two-step conversion of reduction and cyclization provides the bicyclic pyrazolopiperidine 12 in a good yield. A series of pyrazolopiperidine derivatives 18 with a quaternary carbon center at C-3a are stereoselectively synthesized via alkylation or Michael addition.

One-pot cascade synthesis of N-methoxyisoquinolinediones via Rh(iii)-catalyzed carbenoid insertion C–H activation/cyclization

A mild and efficient method for one-pot synthesis of N-methoxyisoquinolinediones via Rh(iii)-catalyzed carbenoid insertion C–H activation/cyclization has been developed.

Domino Prins/pinacol reaction for the stereoselective synthesis of spiro[pyran-4,4′-quinoline]-2′,3′-dione derivatives

A novel series of spiro[pyran-4,4′-quinoline]-2′,3′-dione derivatives have been synthesized in good yields with excellent diastereoselectivity through a cascade of Prins/pinacol reactions.

Ultrasound-assisted solventless synthesis of amines by in situ oxidation/reductive amination of benzyl halides

Ultrasound-assisted solventless oxidation/reductive amination of benzyl halides was developed as a facile, efficient, and environmentally friendly method toward N-alkylated amines.

Intermolecular radical addition to N-acylhydrazones as a stereocontrol strategy for alkaloid synthesis: formal synthesis of quinine

Stereocontrolled Mn-mediated radical addition of alkyl iodides to chiral N-acylhydrazones enables strategic C-C bond disconnection of chiral amines. This strategy was examined in the context of a total synthesis of quinine, generating new findings of functional group compatibility leading to a revised strategy. Completion of a formal synthesis of quinine is presented, validating the application of Mn-mediated radical addition as a useful new C-C bond construction method for alkaloid synthesis. The Mn-mediated addition generates the chiral amine substructure of quinine with complete stereocontrol. Subsequent elaboration includes two successive ring closures to forge the azabicyclo[2.2.2]octane ring system of quincorine, linked to quinine through two known reactions.

Asymmetric allylic alkylation in combination with ring-closing metathesis for the preparation of chiral N-heterocycles

Asymmetric copper-catalyzed allylic substitution with methylmagnesium bromide is employed in combination with ring-closing olefin metathesis or ene-yne metathesis to achieve the synthesis of chiral, unsaturated nitrogen heterocycles. The resulting six- to eight-membered chiral heterocycles are accessible in high yields and with excellent enantioselectivities.

Photochemical reactions as key steps in natural product synthesis

Photochemical reactions contribute in a significant way to the existing repertoire of carbon-carbon bond-forming reactions by allowing access to exceptional molecular structures that cannot be obtained by conventional means. In this Review, the most important photochemical transformations that have been employed in natural product synthesis are presented. Selected total syntheses are discussed as examples, with particular attention given to the photochemical key step and its stereoselectivity. The structural relationship between the photochemically generated molecule and the natural product is shown, and, where necessary, the consecutive reactions in the synthesis are illustrated and classified.

Enamides and enesulfonamides as nucleophiles: formation of complex ring systems through a platinum(II)-catalyzed addition/Friedel-Crafts pathway

Cyclic enamine derivatives (enesulfonamides and enamides) tethered to an 1-arylalkynyl fragment undergo a platinum(II)-catalyzed tandem alkyne addition/Friedel-Crafts ring closure to form nitrogen-containing polycyclic structures. Regioselectivity in the initial addition of the enesulfonamide or enamide nucleophile to the platinum(II)-alkyne complex is important. Electron-rich arenes and heterocycles led to the formation of products resulting from an initial 6-endo cyclization. Twenty-three examples of this process are presented.