Ionic Reactivity of 2-Isocyanoaryl Thioethers: Access to 2-Halo and 2-Aminobenzothia/Selenazoles.

An ionic cascade insertion/cyclization reaction of thia-/selena-functionalized arylisocyanides has been successfully developed for the efficient and practical synthesis of 2-halobenzothiazole/benzoselenazole derivatives. This synthetic protocol, incorporating a halogen atom when forming the five-membered ring of benzothia/selenazoles, is different from the existing ones, where halogenation of the preformed benzothia/selenazole precursors happens. Additionally, a facile access to 2-aminobenzothiazoles is also achieved by the one-pot cascade reaction of 2-isocyanoaryl thioethers, iodine, and amines.

Highly Stable Copper(I)-Thiacalix[4]arene-Based Frameworks for Highly Efficient Catalysis of Click Reactions in Water.

Environmentally friendly metal-organic frameworks (MOFs) have gained considerable attention for their potential use as heterogeneous catalysts. Herein, two CuI -based MOFs, namely, [Cu4 Cl4 L]⋅CH3 OH⋅1.5 H2 O (1-Cl) and [Cu4 Br4 L]⋅DMF⋅0.5 H2 O (1-Br), were assembled with new functionalized thiacalix[4]arenes (L) and halogen anions X- (X=Cl and Br) under solvothermal conditions. Remarkably, catalysts 1-Cl and 1-Br exhibit great stability in aqueous solutions over a wide pH range. Significantly, MOFs 1-Cl and 1-Br, as recycled heterogeneous catalysts, are capable of highly efficient catalysis for click reactions in water. The MOF structures, especially the exposed active CuI sites and 1D channels, play a key role in the improved catalytic activities. In particular, their catalytic activities in water are greatly superior to those in organic solvents or even in mixed solvents. This work proposes an attractive route for the design and self-assembly of environmentally friendly MOFs with high catalytic activity and reusability in water.

Silver-Catalyzed Nucleophilic Addition of ß-Dicarbonyls to Isocyano Group: Facile Access to Indolin-3-ol Derivatives.

A domino silver-catalyzed intermolecularly nucleophilic addition of ß-dicarbonyls to the isocyano group and cyclization of the imidoyl silver sequence was developed for the direct and efficient synthesis of indolin-3-ol derivatives. This domino transformation tolerates a range of readily available o-acyl arylisocyanides and 1,3-dicarbonyls under an operationally simple procedure. Triple roles of silver carbonate are demonstrated in this reaction: (1) activation of isocyano group, (2) formation of enolate, and (3) promotion the nucleophilic reactivity of imidoyl intermediate.

Rhodium-Catalyzed Tandem Reaction of Isocyanides with Azides and Oxygen Nucleophiles: Synthesis of Isoureas.

A novel rhodium-catalyzed tandem reaction of isocyanides with azides and various oxygen nucleophiles has been developed. The reaction provides a simple and highly efficient one-pot synthesis of various N-sulfonyl/acylisoureas with broad substrate scope in an atom-economical manner from readily available starting materials in a highly stereoselective manner.

A Calix[4]resorcinarene-Based [Co12] Coordination Cage for Highly Efficient Cycloaddition of CO2 to Epoxides.

The design and synthesis of polynuclear metal cluster-based coordination cages is of considerable interest due to their appealing structural characteristics and potential applications. Herein, we report a calix[4]resorcinarene-based [Co12] coordination cage, [Co12(TPC4R-I)2(1,3-BDC)10(µ3-OH)4(H2O)10(DMF)2]·7DMF·23H2O (1), assembled with 2 bowl-shaped calix[4]resorcinarenes (TPC4R-I), 10 angular 1,3-benzenedicarboxylates (1,3-BDC), and 12 Co(II) cations. Remarkably, it is shown to be a highly efficient recyclable heterogeneous catalyst for CO2 conversion due to its exposed Co(II) Lewis acid sites.

Polyoxometalate-Bridged Cu(I)- and Ag(I)-Thiacalix[4]arene Dimers for Heterogeneous Catalytic Oxidative Desulfurization and Azide-Alkyne "Click" Reaction.

Two remarkable polyoxometalate-bridged Cu(I)- and Ag(I)-thiacalix[4]arene dimers, namely, [Cu4(SiW12O40)(L)2(DMF)2]·2EtOH·DMF (1-Cu) and [Ag4(PMo12O40)(L)2]·OH (1-Ag), were prepared by using a new thiacalix[4]arene, metal cation and polyoxometalate (L = tetra[2-(ethylthio)-1-methyl-1H-imidazole]-thiacalix[4]arene). In 1-Cu and 1-Ag, two thiacalix[4]arenes were linked together by one [SiW12O40]4- or [PMo12O40]3- anion via two metal cations to give a molecular dimer. Further, adjacent dimers were extended into a high-dimensional supramolecular architecture through hydrogen bonds. Markedly, these molecular dimers are exceedingly stable in organic solvents and then were employed as efficient catalysts for catalytic oxidation desulfurization as well as the azide-alkyne "click" reaction.

Triple Nucleophilic Attack of Nitromethane on (2-Iminoaryl)divinyl Ketones: A Domino Synthetic Strategy for Hexahydrophenanthridinones.

A novel domino reaction of (2-iminoaryl)divinyl ketones with nitromethane was developed for the efficient synthesis of hexahydrophenanthridin-9(5H)-ones. The reaction proceeded smoothly from readily available starting materials under mild reaction conditions to construct three new bonds and two rings with high diastereoselectivities in good to excellent yields in a single step. A mechanism is proposed, involving a stepwise double Michael addition/aza-Henry reaction cascade, and in this transformation, nitromethane acts as a trinucleophile.

Rhodium(iii)-catalyzed three-component cascade synthesis of 6H-benzo[c]chromenes through C-H activation.

A three-component cascade reaction is described that provides concise access to 6H-benzo[c]chromenes via Rh(iii)-catalyzed annulation of aryl ketone O-acyloximes, quinones and acetone. Acetone acts as a co-solvent and as a reactant. This reaction shows high efficiency, atom- and step-economy, good substrate scope, excellent functional group compatibility and gives the products in good yields.

Chemistry of Ketene N,S-Acetals: An Overview.

Push-pull alkenes, which bear electron-donating and -accepting group(s) at both termini of a C═C double bond, respectively, are of interest not only for their unique electronic properties but also for their importance as versatile building blocks in organic synthesis. In the world of ketene acetals having the push-pull alkene skeleton, ketene N,S-acetal is most likely the biggest family according to the number and types of these compounds. The first ketene N,S-acetal compound was reported in 1956. As a cyclic ketene N,S-acetal compound, nithiazine, the first lead structure of neonicotinoid insecticides, was reported in 1978. The characteristics of ketene N,S-acetals, which have the structural feature of ketene S,S-acetals and enaminones, make them versatile and easy to use, especially in cyclization and multicomponent reactions for the synthesis of various heterocyclic systems and related natural products. There has been an increasing wealth of information about the synthesis and synthetic applications of ketene N,S-acetals, especially, in recent years. This review provides comprehensive knowledge on the chemistry of ketene N,S-acetals.

[3+2] Cycloaddition of Tosylmethyl Isocyanide with Styrylisoxazoles: Facile Access to Polysubstituted 3-(Isoxazol-5-yl)pyrroles.

A facile access to polysubstituted 3-(isoxazol-5-yl)pyrroles was developed through [3+2] cycloaddition of tosylmethyl isocyanide (TosMIC) and styrylisoxazoles. In the presence of KOH, various styrylisoxazoles reacted smoothly with tosylmethyl isocyanide and analogs to deliver a wide range of 3-(isoxazol-5-yl)pyrroles at ambient temperature. This transformation is operationally simple, high-yielding, and displays broad substrate scope.

Silver-Catalyzed Chemoselective [4+2] Annulation of Two Isocyanides: A General Route to Pyridone-Fused Carbo- and Heterocycles.

A silver-catalyzed chemoselective [4+2] annulation of aryl and heteroaryl isocyanides with α-substituted isocyanoacetamides was developed for the facile and efficient synthesis of 2-aminoquinolones, naphthyridines, and phenanthrolines. A mechanism for this multistep domino reaction is proposed on the basis of a 13 C-labeling experiment, according to which an unprecedented chemoselective heterodimerization of two different isocyanides generates an α-amidoketenimine intermediate, which undergoes 1,3-amino migration to form an α-imidoylketene, followed by 6 π electrocyclization.

Kinetic Control of Rh(III)-Catalyzed Annulation of C-H Bonds with Quinones: Chemoselective Synthesis of Hydrophenanthridinones and Phenanthridinones.

A temperature-dependent redox-neutral Rh(III)-catalyzed C-H bond annulation of N-methoxybenzamides with quinones was developed for the chemoselective synthesis of hydrophenanthridinones and phenanthridinones. This reaction involves an Rh(III)-catalyzed C-H bond functionalization and a subsequent cyclization through the directing group nucleophilic addition to the carbonyl group at room temperature.

Cross-Cycloaddition of Two Different Isocyanides: Chemoselective Heterodimerization and [3+2]-Cyclization of 1,4-Diazabutatriene.

A new cross-cycloaddition reaction between a wide range of isocyanides and 2-isocyanochalcones (or analogues) was developed for the expeditious synthesis of pyrrolo[3,4-b]indoles under thermal conditions. On the basis of the experimental results and DFT calculations, a mechanism for this domino reaction is proposed involving chemoselective heterodimerization of two different isocyanides to form 1,4-diazabutatriene intermediates, followed by an intramolecular [3+2]-cycloaddition and 1,3-proton shift.

Friedel-Crafts Coupling of Electron-Deficient Benzoylacetones Tuned by Remote Electronic Effects.

Acid-catalyzed electrophilic aromatic substitution for C-C bond formation, commonly referred to as the Friedel-Crafts reaction in recognition of its discoverers, has been one of the most useful reactions in organic chemistry for over a century. However, the Friedel-Crafts reaction cannot occur on a benzene ring having a strongly electron withdrawing group, such as an acyl group, which deactivates the aromatic ring toward electrophilic substitutions and remains a major challenge. Herein, the synthesis of naphthoquinones and 1,3-indandiones, bearing two acyl groups at positions ortho to each other on a benzene ring, are demonstrated by means of copper-catalyzed intramolecular aerobic oxidative acylation of benzoylacetone derivative precursors. This unusual Friedel-Crafts reaction reveals a new activation mode for the in situ polarity reverse of an electron-deficient aromatic ring to a reactive, electron-rich ring tuned by remote electronic effects.

Bicyclization of isocyanides with alkenoyl bis(ketene dithioacetals): access to 6,7-dihydro-1H-indol-4(5H)-ones.

The tandem [3 + 2] cycloaddition/intramolecular imidoyl anion trapping strategy has been successfully applied for the synthesis of 6,7-dihydro-1H-indol-4(5H)-ones from alkenoyl bis(ketene dithioacetals) and tosylmethyl isocyanide. The reaction proceeded smoothly under mild reaction conditions to afford bicyclization products in high to excellent yields in a single step.

Silver-catalyzed P-centered anion nucleophilic addition to isocyanide: access to 2-phosphinoyl indoles/indol-3-ols.

A silver-catalyzed chemoselective cascade nucleophilic addition of a P-centered anion to isocyanides and cyclization reaction was developed for the efficient and practical synthesis of a wide range of 2-phosphinoyl indole and indol-3-ol derivatives. Unlike the well-documented synthesis of phosphorus-functionalized heterocycles via a P-centered radical, an anionic reactivity profile of phosphine oxides is most likely involved in this domino transformation.

EDA Complex-Promoted Cascade Cyclization of Alkynes Enabling the Rapid Assembly of 3-Sulfonylindoles and Vinyl Sulfone Oxindoles.

Herein, we disclose a photoinduced radical cascade cyclization of alkynes with sulfinates via a novel EDA complex for the synthesis of various 3-sulfonylindoles and vinyl sulfone oxindoles, which are crucial motifs in medicinal and biological chemistry. The reaction proceeds under mild, photocatalyst- and transition-metal-free conditions, featuring operational simplicity, broad substrate scope, and easy scalability. Mechanistic studies reveal that the reaction is initiated with a photoinduced intermolecular charge transfer from sulfinates to N-sulfonamides, generating a sulfonyl radical followed by an N-centered radical, thus enabling the cascade cyclization process.

De Novo Synthesis of 2,2'-Bipyridines and Related Bis-azines via Cascade Coupling and Double Pyridannulation of Isocyanides.

Herein, we present a new and general protocol for the assembly of 2,2'-bipyridyls from nonpyridine substrates without using any metal catalysts or organometallic reagents. The process starts from the coupling of two 1,3-dienyl isocyanides followed by a 6π-electrocyclization/aromatization cascade featuring the simultaneous formation of two pyridine rings in a single operation. Notably, this strategy is also applicable to the construction of nonsymmetrical 2-(2-pyridyl)-quinolines/-quinoxalines. Furthermore, the aggregation-induced emission (AIE) characteristics endow our approach with great potential in biorelevant fields.

Efficient synthesis of trifluoromethylated cyclopentadienes/fulvenes/norbornenes from divinyl ketones.

The synthetic methods of trifluoromethylated cyclopentadienes/fulvenes/norbornenes have been developed using 3-CF3-1,4-dien-3-ols as the synthons, which can be easily prepared by the regiospecific 1,2-addition of the Ruppert­Prakash reagent (TMSCF3) to divinyl ketones. All the reactions are carried out under mild, metal-free conditions to afford the corresponding products in high to excellent yields.

Tandem Michael addition/isocyanide insertion into the C-C bond: a novel access to 2-acylpyrroles and medium-ring fused pyrroles.

A new reaction model, tandem Michael addition/formal isocyanide insertion into the acyl C-C bond, has been developed. Thus, a series of 2-acylpyrroles and seven-/eight-membered ring fused pyrroles were synthesized from the reaction of methyl isocyanides with enones in a single operation.