Palladium-Catalyzed Synthesis of 1H-Indenes and Phthalimides via Isocyanide Insertion

C-H functionalization enabled by multiple isocyanides

Past decades have witnessed significant advance of isocyanides as a class of versatile organic synthons as well as their broad applications in multi-component reactions (MCRs) and other tandem reactions. Reactions involving multiple isocyanides allow the construction of molecules with further diversification and complexity, while C-H functionalization emphasizes the advantages of high atom economy, broad substrate availability and great synthetic efficiency. This promising synergistic strategy of C-H functionalization involving multiple isocyanides provides a variety of valuable synthetic methods for organic chemists' toolbox and offers considerable potential in pharmaceutical chemistry and materials science as well. The present review outlines in detail various reaction types of C-H functionalization enabled by multiple isocyanides, and the relevant mechanistic rationale is discussed.

Phthalimides: developments in synthesis and functionalization

Phthalimides, an important class of biologically active N-heterocycles, are not only found in pharmaceuticals, natural products, agrochemicals, polymers, and dyes, but also serve as building blocks in organic transformations. Many synthetic methods, including metal catalysis and metal-free systems, have been developed to prepare functionalized phthalimides. In this review, we describe the developments in the synthesis and functionalization of phthalimides over the past two decades.

Synthesis of Polysubstituted Pyrimidines through Palladium-Catalyzed Isocyanide Insertion to 2H-Azirines

The domino process of the palladium-catalyzed coupling reaction of isocyanides with 2H-azirine provides various tetrasubstituted pyrimidines via one C-C bond and two C-N bond formations with satisfactory yields. The title compounds are obtained with good functional group tolerance, high atom economy, and broad substrate scopes.

Direct Access to 2,3-Disubstituted Amido-Indenones through Annulation of 2-Iodobenzaldehydes with Ynamides

In this paper we report the annulation reaction between 2-iodobenzaldehyde derivatives and various ynamides. This palladium-catalyzed reaction leads to rare polysubstituted amino-indenones in good yields with a regioselectivity up to complete. Remarkably, a regiodivergent selectivity has been identified between aryl and alkyl or silyl ynamides, with the first leading mainly to 2-amido-indenones and the second to 3-amido-indenones.

Oxidative C-H/N-H Carbonylation of Benzamide by Nickel Catalysis with CO as the Carbonyl Source

An efficient and direct carbonylation of aminoquinoline benzamides has been developed using abundant and inexpensive Ni(OAc)₂·4H₂O as the catalyst and carbon monoxide as a cost-efficient C1 building block. This process features good functional-group tolerance and can be conducted on gram scale. The directing group can be easily removed under mild conditions.

Recent advances in the synthesis of cyclic compounds using α,α-dicyanoolefins as versatile vinylogous nucleophiles

This article provides a review of the applications of α,α-dicyanoolefins as versatile vinylogous nucleophiles in the synthesis of various cyclic compounds, covering the literature from the past 13 years.

Divergent Reaction of Isocyanides with o-Bromobenzaldehydes: Synthesis of Ketenimines and Lactams with Isoindolinone Cores

A divergent reaction of isocyanides with o-bromobenzaldehydes for the synthesis of isoindolinone-derived ketenimines and lactams was disclosed. The reaction features readily available reactants, relatively mild conditions, and high yields of products. Ketenimines could be applied in further transformations for access to other functional molecules. A mechanism study showed that the palladium-migration/imine-insertion process was the key step in this reaction.

Equivalent Loading of Directed Arenes in Pd(II)-Catalyzed Oxidative Cross-Coupling of Aryl C-H Bonds at Room Temperature

The unsymmetrical biaryls (Ar¹-Ar²) produced by the catalytic cross-couplings of aryl halides (Ar¹-halo) with aryl metallics (Ar²-M) in the loading ratio of 1:1 are popular in chemical synthesis. In contrast, there has been less precedence on the same biaryls produced effectively from two normal aryl C-H bonds with equivalent loading. Here, we report that, in a palladium/oxidant/acid catalytic system at room temperature, one arene (Ar¹-H, 1 equiv) can highly selectively couple with the other one (Ar²-H, 1 equiv) to afford the target Ar¹-Ar² just by controlling the directing groups and the substituted groups on their phenyl rings. The utility of this one-one cross-coupling is also demonstrated by synthesis of a few bioactive molecules.

Synthesis of Substituted Phthalimides via Ultrasound-Promoted One-Pot Multicomponent Reaction

In this work, a novel strategy for the straightforward synthesis of substituted phthalimides is described, which includes base-mediated Michael addition/intramolecular cyclization/[1,5]-H shift/cleavage of CS₂/aromatization/nucleophilic acyl substitution reaction of 2-(4-oxo-2-thioxothiazolidin-5-ylidene)acetates and α,α-dicyanoolefines under ultrasound (US) irradiation. Some advantages of this method are as follows: having simple operation, easily accessible starting materials, chemoselective cascade process, synthetically useful yields, and green conditions by utilizing US irradiation as a source of energy and using ethanol as solvent.

Beyond conventional construction of the phthalimide core: a review

This review highlights (2010–2021) different strategies for the construction of the phthalimide core apart from traditional synthetic routes.

Recent Advances in Palladium-Catalyzed Isocyanide Insertions

Isocyanides have long been known as versatile chemical reagents in organic synthesis. Their ambivalent nature also allows them to function as a CO-substitute in palladium-catalyzed cross couplings. Over the past decades, isocyanides have emerged as practical and versatile C1 building blocks, whose inherent N-substitution allows for the rapid incorporation of nitrogeneous fragments in a wide variety of products. Recent developments in palladium catalyzed isocyanide insertion reactions have significantly expanded the scope and applicability of these imidoylative cross-couplings. This review highlights the advances made in this field over the past eight years.

Transition metal-free NaOH-catalyzed hydration of nitriles to primary amides in NH3·H2O-DMSO mixture

In this paper, we reported an efficient protocol for hydration of aryl(hetero) and alkyl nitriles toward primary amides with 0.1 equiv. NaOH in NH₃·H₂O-DMSO under mild conditions. Various substituted nitriles are smoothly converted to the corresponding amides with good to excellent isolated yields. Gram-scale reactions were also performed to produce the desired products in high yields. In addition, the excessive hydrolysis of the nitrile to form the corresponding carboxylic acid was also achieved with increasing the amount of NaOH and prolonging the reaction time.

Assembly of 1H-isoindole derivatives by selective carbon-nitrogen triple bond activation: access to aggregation-induced emission fluorophores for lipid droplet imaging

A method of selectively activating carbon–nitrogen triple bonds has been developed to access 1H-isoindole AIE fluorophores for lipid droplet imaging.

A novel strategy has been established to assemble a series of single (Z)- or (E)-1H-isoindole derivatives through selectively and sequentially activating carbon–nitrogen triple bonds in a multicomponent system containing various nucleophilic and electrophilic sites. The reaction provides efficient access to structurally unique fluorophores with aggregation-induced emission characteristics. These new fluorophores show fluorescence wavelengths and efficiencies that can be modulated and have excellent potential to specifically light up lipid droplets (LDs) in living cells with bright fluorescence, low cytotoxicity and better photostability than commercially available LD-specific dyes.

Porous Organic Polymer-Derived Nanopalladium Catalysts for Chemoselective Synthesis of Antitumor Benzofuro[2,3- b]pyrazine from 2-Bromophenol and Isonitriles

An efficient strategy for the synthesis of benzofuro[2,3- b]pyrazines was developed. These tricyclic scaffolds were formed through a multistep cascade sequence, which includes double insertion of isonitriles and chemoselective bicyclization. In this reaction, a nanopalladium was used as a recyclable catalyst. Product 3w exhibited excellent anticancer activity toward T-24 (IC₅₀ = 12.5 ± 0.9 μM) and HeLa (IC₅₀ = 14.7 ± 1.6 μM) cells. We also explored the action mechanism of 3w on T-24 cells.

Synthesis of iminoisoindolinones via a cascade of the three-component Ugi reaction, palladium catalyzed isocyanide insertion, hydroxylation and an unexpected rearrangement reaction

A robust ligand-free palladium-catalyzed cascade reaction for the synthesis of diversely substituted iminoisoindolinones has been developed. The cascade reaction involves isocyanide insertion into Ugi-3CR adducts, accompanied by unexpected hydroxylation and rearrangement.

Cascade double isocyanide insertion and C-N coupling of 2-iodo-2'-isocyano-1,1'-biphenyls

A palladium-catalyzed double isocyanide insertion using 2-iodo-2'-isocyano-1,1'-biphenyls followed by copper-catalyzed intramolecular C-N coupling, delivering a unique heterocyclic structure containing both phenanthridine and carbazole scaffolds, has been developed. In this cascade process, four chemical bonds, including two C-C, one C-O, and one C-N bonds are formed consecutively without isolating an intermediate. The strategy of using a functionalized isocyanide in double insertion provides a quick approach for constructing heterocyclic systems with high bond-forming efficiency.

Palladium-Metalated Porous Organic Polymers as Recyclable Catalysts for the Chemioselective Synthesis of Thiazoles from Thiobenzamides and Isonitriles

Two types of thiazole derivatives are synthesized through a multistep cascade sequence with Pd-metalated phosphorus-doped porous organic polymers (POPs) as heterogeneous catalysts. The POPs could be used as both ligands and catalyst supports. No obvious aggregation and loss of any catalytic activity of the catalysts were observed after 10 runs of the reaction. More importantly, imidazo[4,5- d]thiazoles, which are a new class of thiazole derivatives, could be obtained through K₂CO₃-promoted intramolecular cyclization of the synthesized polysubstituted thiazoles. Furthermore, the in vitro anticancer activity of these new compounds were tested with MTT assay, and compound 4b exhibited good antitumor activity toward T-24 and A549 cells with IC₅₀ values of 10.3 ± 0.8 and 11.8 ± 0.5 μM, respectively. In addition, the action mechanism of 4b on tumor cells was determined.