Enantioselective Synthesis of Isoindolinone by Palladium-Catalyzed Aminoalkynylation of O-Phenyl Hydroxamic Ethers with Alkynes.

A highly efficient palladium-catalyzed asymmetric tandem aza-Heck/Sonogashira coupling reaction of O-phenyl hydroxamic ethers with terminal alkynes is described. This protocol enables versatile access to challenging chiral isoindolinone derivatives bearing a quaternary stereogenic center. The palladium-catalyzed aminoalkynylation reaction shows broad functional group tolerance and allows the straightforward preparation of isoindolinones with high efficiency and excellent enantioselectivity under mild conditions. DFT calculations were performed to disclose the reaction mechanism and the origins of the enantioselectivity.

Construction of Diverse Fused Chromene Frameworks via Isocyanide-Based Three-Component Reaction.

A convenient synthetic protocol for diverse fused chromenes was successfully developed by a three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and various cyclic 1,3-dipolarophiles containing o-hydroxyphenyl group. In the absence of any catalyst, the three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and 3-(o-hydroxyarylidene)indolin-2-ones in tetrahydrofuran at 60 °C resulted in unique functionalized spiro[cyclobuta[c]chromene-1,3'-indolines] in good yields and with high diastereoselectivity. However, the similar three-component reaction with 2-(5-halo-2-hydroxyarylidene)indolin-2-ones afforded unexpected chain products in satisfactory yields. In addition, the three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and 2-(o-hydroxyarylidene)-1,3-indanediones in tetrahydrofuran at 60 °C resulted in complex indeno[2',1':5,6]pyrano[3,4-c]chromene derivatives in high yields and with high diastereoselectivity.

Synthesis of Bis-Heterocycles Bearing Methyleneindole Motifs by Pd-Catalyzed Domino Reaction.

A highly robust, general, and practically simple palladium-catalyzed domino bicyclization strategy is presented to synthesize nitrogen-containing bis-heterocycles bearing methylene indole motifs from alkyne-tethered carbamoyl chlorides and ß,γ- or γ,δ-unsaturated hydrazones. The salient features of this transformation include broad substrate scope, good functional group tolerance, ease for scale-up, and convenient conversion.

Visible-Light-Induced and Iodoform-Promoted Functionalization of Ether with Secondary Sulfonyl Amides.

An iodoform-promoted functionalization of ether with secondary sulfonyl amides under visible-light irradiation was developed toward synthesis of hemiaminal skeleton with good to excellent isolated yields. The characterization of the isolated ether and iodoform complex revealed regioselective hydrogen atom transfer to initiate carbon radical formation and enabled the amination reaction with the sulfonamide.

Synthesis of Sulfoxides by Palladium-Catalyzed Arylation of Sulfenate Anions with Aryl Thianthrenium Salts.

A novel and highly efficient Pd-catalyzed arylation of sulfenate anions with aryl thianthrenium salts is demonstrated. This procedure provides a practical protocol to synthesize various diaryl and alkyl aryl sulfoxides in moderate-to-good yields. The new approach shows mild reaction conditions, broad substrate scope, and good functional group tolerance.

Anthracene-induced formation of highly twisted metallacycle and its crystal structure and tunable assembly behaviors.

Polycyclic aromatic hydrocarbons (PAHs) continue to attract increasing interest with respect to their applications as luminescent materials. The ordered structure of the metal-organic complex facilitates the selective integration of PAHs that can be tuned to function cooperatively. Here, a unique highly twisted anthracene-based organoplatinum metallacycle was prepared via coordination-driven self-assembly. Single-crystal X-ray diffraction analysis revealed that the metallacycle was twisted through the cooperation of strong π···π stacking interactions and steric hindrance between two anthracene-based ligands. Notably, the intramolecular twist and aggregation behavior introduced restrictions to the conformational change of anthracenes, which resulted in increased emission intensity of the metallacycle in solution. The emission behaviors and suprastructures based on the highly twisted metallacycle can be modulated by the introduction of different solvents. This study demonstrates that this metallacycle with highly twisted structure is a promising candidate for sensing and bioimaging applications.

Rapid construction of tricyclic tetrahydrocyclopenta[4,5]pyrrolo[2,3-b]pyridine via isocyanide-based multicomponent reaction.

An efficient protocol for the synthesis of polyfunctionalized tetrahydrocyclopenta[4,5]pyrrolo[2,3-b]pyridine-3,4b,5,6,7(1H)-pentacarboxylates was developed by a three-component reaction. In the absence of any catalyst, the three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates and 5,6-unsubstituted 1,4-dihydropyridines in refluxing acetonitrile afforded polyfunctionalized tetrahydrocyclopenta[4,5]pyrrolo[2,3-b]pyridine-3,4b,5,6,7(1H)-pentacarboxylates in high yields and with high diastereoselectivity. The reaction was finished by in situ generation of activated 5-(alkylimino)cyclopenta-1,3-dienes from addition of alkyl isocyanide to two molecules of but-2-ynedioates and sequential formal [3 + 2] cycloaddition reaction with 5,6-unsubstituted 1,4-dihydropyridine.

Visible-Light Photoredox Catalyzed Regioselective 1,4-Hydroalkylation of 1,3-Enyne.

Described herein is a visible-light photoredox-catalyzed regioselective 1,4-hydroalkylation of 1,3-enynes. Various of di- and tri-substituent allenes were really accessible under the present reaction conditions. The visible-light photoredox activation of the carbon nucleophile to generate its radical species, allowing the addition with un-activated enynes. The synthetic utility for the present protocol was demonstrated by a large-scale reaction, as well as the derivatization of the allene product.

Convenient Synthetic Protocols for Diverse Functionalized Dihydrobenzofuran-Fused Spiro-indanedione-oxindole Scaffolds.

Diverse functionalized dihydrobenzofuran spiro-indanedione-oxindole scaffolds were conveniently synthesized by base-promoted cyclization reaction of Morita-Baylis-Hillman (MBH) carbonates of isatins and 2-(o-hydroxybenzylidene)-1,3-indanediones. The two diastereomeric dispiro[indene-2,1'-cyclopenta[b]benzofuran-2',3″'-indolines] could be selectively synthesized by using DABCO or DMAP as a base promoter. More importantly, DABCO or DMAP facilitated the annulation reaction of MBH formates of isatins and 2-(o-hydroxybenzylidene)-1,3-indanediones selectively, resulting in spiro[cyclopropa[c]chromene-1,2'-indene]-1',3'-diones or dispiro[indene-2,1'-cyclopenta[b]benzofuran-2',3″'-indolines]. Additionally, a similar reaction with MBH maleimides of isatins afforded dispiro[indene-2,5'-benzofuro[2',3':1,5]cyclopenta[1,2-c]pyrrole-4',3″'-indolines] in high yields and with high diastereoselectivity.

Construction of Unique Spiro[dibenzo[a,f]azulene-6,2'-indenes] via Unprecedented Annulation of ortho-C-H Bond of Benzylidene Group.

The domino reaction of alkyl and aryl isocyanides with two molecules of 2-arylidene-1,3-indanediones in acetonitrile at 80 °C resulted in unique functionalized spiro[dibenzo[a,f]azulene-6,2'-indenes] in good yields, in which the two 2-arylidene-1,3-indanediones acted as different building blocks to construct the polycyclic system. More importantly, the unprecedented anticipation of the ortho-position of benzylidene group to form a novel dibenzo[a,f]azulene ring through a formal [5 + 2] cycloaddition process was first observed. On the other hand, DABCO-promoted reaction of the isocyanides with two molecules of 2-arylidene-1,3-indanediones in acetonitrile at 80 °C afforded functionalized spiro[cyclopenta[a]-indene-2,2'-indene] derivatives.

Regioselective and Diastereoselective Construction of Diverse Dispiro-Indanone-Fluorenone-Oxindole Motifs.

A convenient synthetic protocol for regioselective and diastereoselective construction of complex dispiro-indanone-fluorenone-oxindole motifs was developed by the base-promoted annulation reaction of bindone and MBH carbonates of isatins by adjusting reaction conditions. DABCO promoted the annulation reaction of bindone and MBH carbonates of isatins in DCM at room temperature, affording dispiro[indene-2,4'-fluorene-1',3″-indoline] derivatives in good yields and with high diastereoselectivity. Triethylamine promoted the annulation reaction of two molecular 1,3-indanediones and MBH esters of isatins in ethanol at elevated temperature and selectively gave dispiro[indene-2,4'-fluorene-3',3″-indolines] in moderate yields. However, triethylamine promoted the annulation reaction of excess 1,3-indanediones and MBH esters of isatins in refluxing ethanol, affording dispiro[indene-2,4'-fluorene-3',3″-indolines] with the Z-isomer as the major product and the E-isomer as the minor product.

Acid-Modulated Construction of Cyclopenta[b]indole and Cyclohepta[b]indole via Unprecedented C3/C2 Carbocation Rearrangement.

p-TsOH-catalyzed cycloaddition of various 3-vinylindoles and (indol-2-yl)diphenylmethanols in acetonitrile gave the functionalized cyclopenta[b]indoles in good yields and with high diastereoselectivity via [3 + 2] cycloaddition reaction. More importantly, FeCl3-catalyzed annulation reaction afforded unexpected functionalized cyclohepta[1,2-b:4,5-b']diindoles in satisfactory yields, in which a formal [4 + 3] cycloaddition and an unprecedented C3/C2 carbocation rearrangement were first confirmed by the determination of single-crystal structure.

Photoinduced Copper-Catalyzed 1,2-Difunctionalization of 1,3-Dienes with Aryl Diselenides.

Described herein is a photoinduced copper-catalyzed 1,2-difunctionalization of 1,3-dienes. The selenium atom radical was generated by the visible light irradiation of diselenides, triggering radical addition with 1,3-dienes to form allyl radical intermediate. Subsequent rapid Z/E isomerization allowed for thermodynamically favorable intermediate formation and enabled copper catalyzed stereoselective functionalization with various nucleophiles.

Visible-Light-Mediated Radical Hydroalkylative Cyclization of 1,6-Enynes.

A radical hydroalkylative cyclization approach accessing various alkenyl heterocyclic compounds was developed using dimethyl malonate and 1,6-enynes in the presence of visible-light photoredox catalysis. The use of Ir(dtbbpy)(ppy)2PF6 as a photosensitizer enables carbon atom radical formation and initiates the cascade cyclization reaction under mild conditions.

Emissive Nanoparticles from Co-assembly of Metallatetragon and Amphiphilic Tetraphenylethylene for Cancer Theranostics.

Platinum(II)-based metallacycles/cages have obtained tremendous attention due to their fascinating topology and wide range of applications, such as fluorescent materials, cell imaging, and tumor treatment. In this work, a metallatetragon (1) was constructed from 4-(4-(1,2,2-triphenylvinyl)phenyl)pyridine (2) and 90° cis-Pt(II) (Pt) in acetone through the strategy called "coordination driven self-assembly". Interestingly, through co-assembly of 1 and poly(ethylene glycol)-modified tetraphenylethylene (TPE-PEG22), fluorescent nanotheranostics, which could generate singlet oxygen (1O2) under the NIR irradiation and release Pt drugs under a low-pH microenvironment, were prepared successfully. The obtained theranostics could realize living cell imaging and synergistic chemo-photodynamic therapy in vitro and in vivo.

Pillar[5]arene-Derived Terpyridinepalladium(II) Complex: Synthesis, Characterization, and Application in Green Catalysis.

Metal nanoparticle catalysts have attracted great interest because they possess high surface-to-volume ratios and exhibit a very large number of catalytically active sites per unit area. However, high surface-to-volume ratios will induce nanoparticle aggregates during the catalytic reactions, making them lose their catalytic activity. In this work, a monoterpyridine-unit-functionalized pillar[5]arene (TP5) was synthesized successfully, which can be used as anchoring sites for the controllable preparation of well-dispersed palladium nanoparticles [TP5/Pd(0) NPs]. The as-prepared TP5/Pd(0) NPs were fully characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, and powder X-ray diffraction. Importantly, the ultrafine TP5/Pd(0) NPs are found to be excellent and reusable catalysts for the reduction of nitrophenols in aqueous solution.

Construction of diverse spirooxindoles via a domino reaction of arylamines, but-2-ynedioates and 3-hydroxy-3-(indol-3-yl)indolin-2-ones.

An iodine-promoted domino reaction of arylamines/benzylamines, dialkyl but-2-ynedioates and 3-hydroxy-3-(indol-3-yl)indolin-2-ones showed very interesting molecular diversity. The reaction in acetonitrile at 65 °C in the presence of 30% mmol I2 resulted in spiro[indoline-3,1'-pyrido[4,3-b]indoles] in satisfactory yields. When anilines without para-substituents were used in the reaction, a direct substitution of the hydroxyl group to 2-(phenylamino)maleate at the para-position of aniline gave chain products in good yields. Additionally, similar reactions with benzylamines not only gave spiro[indoline-3,1'-pyrido[4,3-b]indoles], but also afforded spiro[indoline-3,1'-pyrano[4,3-b]indol]-2-ones in lower yields. A plausible domino annulation mechanism was rationally proposed for the formation of different kinds of polycyclic compounds.

Tandem ring-opening and formal [3 + 2] cycloaddition of furo[2,3-d]pyrimidine-2,4-diones.

The base promoted tandem annulation reaction of activated cyclic 1,3-dipolarophiles such as 2-arylidene-1,3-indanediones, 2-(o-hydroxybenzylidene)-1,3-indanediones and 3-methyleneoxindoles with functionalized furo[2,3-d]pyrimidine-2,4-diones was systematically investigated. This reaction provided efficient synthetic protocols for complex dispiro/dispiro fused tricyclic compounds including dispiro[indene-2,3'-cyclopentane-1',5''-pyrimidines], dispiro[indoline-3,3'-cyclopentane-1',5''-pyrimidines] and spiro[cyclopenta[c]indeno[1,2-b]chromene-3,5'-pyrimidines] in good yields and with high diastereoselectivity. The reaction was believed to proceed via sequential ring-opening of the furyl ring, formal [3 + 2] cycloaddition and annulation of the o-hydroxyphenyl group.

Pd/Cu-catalyzed cascade Heck-type reactions of alkenyl halides with terminal alkynes toward substituted pyrrolidine analogues.

Pd/Cu-catalyzed cascade Heck-type reactions of alkenyl halides with terminal alkynes have been developed. This research provides an efficient atom-economical approach to access a variety of highly substituted pyrrolidines in moderate to good yields. This protocol features readily available substrates, broad substrate scope, easy scale-up, high selectivities and versatile transformations.

Merging Visible Light Photocatalysis and P(III)-Directed C-H Activation by a Single Catalyst: Modular Assembly of P-Alkyne Hybrid Ligands.

Metal-catalyzed C-H activation strategies provide an efficient approach for synthesis by minimizing atom, step, and redox economy. Developing milder, greener, and more effective protocols for these strategies is always highly desirable to the scientific community. In this study, the utilization of a single rhodium complex enabled the visible-light-induced late-stage C-H activation of biaryl-type phosphines with alkynyl bromides, employing inherent phosphorus atoms as directing groups. This chemistry combines P(III)-directed C-H activation with visible light photocatalysis, under exogenous photosensitizer-free conditions, offering a unique platform for ligand design and preparation. Furthermore, this study also explores the asymmetric catalysis and coordination chemistry of the resulting P-alkyne hybrid ligands with specific transition metals. Experimental results and density functional theory calculations demonstrate the mechanistic intricacies of this transformation.