Unusual Solid-State Luminescent Push−Pull Indolones: A General One-Pot Three-component Approach

Pd-catalyzed 5-exo-dig cyclization/etherification cascade of N-propargyl arylamines for the synthesis of polysubstituted furans

A method for the synthesis of furans bearing indoline skeletons was developed via an intramolecular palladium-catalyzed 5-exo-dig cyclization/etherification cascade of N-propargyl arylamines containing a 1,3-dicarbonyl side chain. This method realized the first capture of vinyl carbopalladiums by ketones as O-nucleophiles and showed a wide range of substrate tolerability affording trisubstituted furans in various yields. The enantioselective version for this domino process and diverse derivatizations of the reaction products were also studied.

Multicomponent synthesis of chromophores – The one-pot approach to functional π-systems

Multicomponent reactions, conducted in a domino, sequential or consecutive fashion, have not only considerably enhanced synthetic efficiency as one-pot methodology, but they have also become an enabling tool for interdisciplinary research. The highly diversity-oriented nature of the synthetic concept allows accessing huge structural and functional space. Already some decades ago this has been recognized for life sciences, in particular, lead finding and exploration in pharma and agricultural chemistry. The quest for novel functional materials has also opened the field for diversity-oriented syntheses of functional π-systems, i.e. dyes for photonic and electronic applications based on their electronic properties. This review summarizes recent developments in MCR syntheses of functional chromophores highlighting syntheses following either the framework forming scaffold approach by establishing connectivity between chromophores or the chromogenic chromophore approach by de novo formation of chromophore of interest. Both approaches warrant rapid access to molecular functional π-systems, i.e. chromophores, fluorophores, and electrophores for various applications.

Electrophile-Promoted Nucleophilic Cyclization of 2-Alkynylindoles to Give 4-Substituted Oxazinoindolones

A method for the synthesis of 4-organoselanyl oxazinoindolone derivatives by the cascade cyclization of N-(alkoxycarbonyl)-2-alkynylindoles using iron(III) chloride and diorganyl diselenides as promoters was developed. This protocol was applied to a series of N-(alkoxycarbonyl)-2-alkynylindoles containing different substituents. The reaction conditions also tolerated a variety of diorganyl diselenides having both electron donating and electron withdrawing groups. However, the reaction did not work for diorganyl disulfides and ditellurides. The reaction mechanism seems to proceed via an ionic pathway and the cooperative action between iron(III) chloride and diorganyl diselenides is crucial for successful cyclization. We also found that using the same starting materials, by simply changing the electrophilic source to iodine, led to the formation of 4-iodo-oxazinoindolones. The high reactivity of Csp² -Se and Csp² -I bonds were tested under cross-coupling conditions leading to the preparation of a new class of functionalized indole derivatives. In addition, the absorption, emission and electrochemical properties of 4-organoselanyl oxazinoindolones showed an important relationship with the substituents of the aromatic rings. The advantages of the methodology include the use of electrophilic to promote the cyclization reaction and functionalization of the indole ring, and the electronic properties presented by the prepared compounds can be exploited as probes, analyte detectors and optical materials.

Binaphthyl-Stabilized Palladium Nanoparticle-Catalyzed Stereoselective Synthesis of 3-Arylidene-2-oxindoles via One-Pot Heck-like Carbocyclization/Nucleophilic Addition

Stereoselective, one-pot synthesis of 3-arylidene-2-oxindoles has been accomplished via Heck-like carbocyclization/nucleophilic addition of N-(2-iodophenyl)-N-methyl-3-phenylpropiolamide, phenylacetylene, and secondary amine using binaphthyl stabilized palladium nanoparticles (Pd-BNP) as a reusable catalyst. Less reactive aryl bromides generally provided a similar yield of 3-arylidene-2-oxindoles compared with more reactive aryl iodides. The Pd-BNP nanocatalyst has been recovered and recycled for five catalytic cycles with only an insignificant reduction in particle size, reactivity, and reaction yield.

Stereoselective Construction of Unsymmetrically Linked Heterocycles via Palladium-Catalyzed Alkyne Insertion/Cycloimidoylation Cascade

A novel strategy to access unsymmetrically linked heterocycles via palladium-catalyzed acylcycloimidoylation of alkyne-tethered carbamoyl chlorides with isocyanides has been developed. Functionalized isocyanides were successfully applied as imine-containing heterocycle precursors to capture the vinyl-Pd^II intermediate, which was generated from a syn-carbopalladation of alkyne, followed by subsequent intramolecular C-H bond activation/imidoylative Heck reactions. Methylene oxindoles within Z-tetrasubstituted olefins were obtained in high yields with excellent stereoselectivities. Broad functional groups were well tolerated under mild reaction conditions.

Pd-Catalyzed alkynyl aryl iodide cyclization/alkylation with cyclobutanols

A palladium-catalyzed cis-selective carboalkylation of internal alkynes with cyclobutanols is reported, providing a useful and facile approach to alkyl-substituted olefins with moderate to good yields and excellent stereoselectivity.

Three-Component Suzuki-Knoevenagel Synthesis of Merocyanine Libraries and Correlation Analyses of Their Oxidation Potentials and Optical Band Gaps

The Suzuki coupling Knoevenagel condensation one-pot synthesis of boronic acids/esters, (hetero)aromatic bromo aldehydes and methylene active compounds is a highly practical consecutive three-component process to provide substance libraries with 60 donor-π-bridge-acceptor molecules, i.e., merocyanines in a broader sense, in moderate to excellent yield. As already seen with the naked eye, a broad variation of the optical properties becomes accessible using this practical synthetic tool. More systematically, correlation analyses upon plotting the optical band gaps against the first oxidation potentials of redox active systems of consanguineous series furnishes linear correlations and, by extension, two parameter plots (oxidation potential and emission maximum) planar correlations with the optical band gaps.

Palladium-catalysed cyclisation of ynamides and propargyl tethered iodosulfonamides with boronic acids leading to benzosultams

An efficient and straightforward Pd-catalysed synthesis of diversely substituted sultams utilising ynamides and boronic acids is disclosed; toluene was found to be the most suitable solvent for this transformation. This strategy has been successfully applied to generate dihydrobenzo[d]isothiazole 1,1-dioxides and dihydro-2H-benzo[e][1,2]thiazine 1,1-dioxides. The advantages of this protocol are good functional group tolerance, broad substrate scope, high-yielding reaction and low catalyst loading to access benzofused sultams with five-/six-membered rings. The synthetic utility has been demonstrated by a gram-scale synthesis. A plausible catalytic cycle involving carbopalladation has been proposed for this transformation.

One-pot synthesis of a white-light emissive bichromophore operated by aggregation-induced dual emission (AIDE) and partial energy transfer

Consecutive four-component insertion–alkynylation–amination–Suzuki sequence furnishes bichromophores that emit white light upon aggregation-induced dual emission (AIDE) operating by partial energy transfer between the constituting chromophores.

Direct Construction of Acid-Responsive Poly(indolone)s through Multicomponent Tandem Polymerizations

Multicomponent polymerizations (MCPs) as a burgeoning field in polymer chemistry has proved to be a powerful and popular tool for the synthesis of functional polymer materials with diverse and complex structures. To explore the general applicability of MCPs and enrich the product structures of MCPs, multicomponent tandem polymerizations (MCTPs) with great synthetic simplicity and efficiency were pursued. In this work, MCTPs of N-(2-iodophenyl)-3-phenyl-N-tosylpropiolamide, aromatic terminal alkynes, and diamines were explored through combining Sonogashira coupling and Michael addition reaction in a one-pot procedure. The MCTPs could proceed efficiently and conveniently under mild conditions with Pd(PPh₃)₂Cl₂, CuI, and i-Pr₂NEt, affording 12 poly(indolone)s with unique structures and high M_ws (up to 30400 g/mol) in high yields (up to 97%). The poly(indolone)s possess a unique acid-triggered fluorescence "turn-on" response which could realize specific detection of CF₃SO₃H from other inorganic and organic acids through a rapid acid-catalyzed reaction from enamine to ketone.

Multi-component synthesis of fluorophores via catalytic generation of alkynoyl intermediates

This account summarizes recent developments of aggregation-induced emissive and emission solvatochromic fluorophores by multicomponent reactions. Key intermediates are catalytically generated alkynoyl derivatives that are directly transformed into luminophores in a one-pot fashion. The conciseness in combination with ready access to tailored chromophore libraries makes this synthetic methodological concept superior over classical multistep syntheses.

Palladium-Catalyzed Domino Reaction for Stereoselective Synthesis of Multisubstituted Olefins: Construction of Blue Luminogens

The first Pd-catalyzed multicomponent reaction of aryl iodides, alkenyl bromides, and strained alkenes has been developed, which allowed us to synthesize a variety of multisubsituted olefins in yields of 45-96% with excellent stereoselectivity. The configuration of the product was controlled by the configuration of the alkenyl bromides. Moreover, this practical methodology employing readily available substrates was found to be tolerant to a wide range of functional groups. Fifty six examples of highly stereoselective tri- or tetrasubstituted olefins have been successfully synthesized via this methodology. Most of the synthesized tetrasubstituted olefins are good aggregation-induced emission (AIE) luminogens.

Multicomponent syntheses of functional chromophores

Multicomponent reactions are a valuable tool for the synthesis of functional π-electron systems. Two different approaches can be taken into account for accessing the target structures. In the more conventional scaffold approach an already existing chromophore is coupled with other components to give a complex functional π-system. Here, electronically monotonous components can also be introduced, which may exert synergistic electronic effects within the novel compound. The more demanding chromophore concept generates a complete π-electron system and a scaffold concurrently. The latter approach is particularly stimulating for methodologists since π-systems might be accessible from simple starting materials. This review encompasses the advances in the preparation of functional π-electron systems via multicomponent processes during the past few years, based both on the scaffold and chromophore concepts. Besides the synthetic strategies the most important properties, i.e. redox potentials, absorption and emission maxima or fluorescence quantum yields, of the synthesized molecules are highlighted.

Fluorophores based on a minimal thienylthiazole core: towards multifunctional materials with solid state red emissions, solvatochromism and AIE behaviour

Minimal architecture solid red emissive D–A–D–A tetrads were built on a thienylthiazole core and their photophysical properties were investigated.

Diversity-oriented synthesis of intensively blue emissive 3-hydroxyisoquinolines by sequential Ugi four-component reaction/reductive Heck cyclization

A convergent approach to highly functionalized 3-hydroxyisoquinolines is reported. The key steps are an Ugi multicomponent reaction and a subsequent intramolecular reductive Heck reaction; these can also be performed as a one-pot procedure. The structures display very interesting properties as blue-fluorescence emitters. Photophysical studies on the absorption and static fluorescence indicate that the substitution pattern on the pyridyl part influences the optical properties only to a minor extent, unless the amide substituent becomes sterically demanding and leads to significant nonradiative deactivation. The donor substitution on the benzo core considerably enhances the fluorescence quantum yields and trimethoxy substitution causes a pronounced redshift of the emission bands. Protonation of the isoquinolyl nitrogen atom causes efficient static quenching of the fluorescence.

One-pot three-component synthesis and photophysical characteristics of novel triene merocyanines

Novel triene merocyanines, i.e. 1-styryleth-2-enylidene and 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones are obtained in good to excellent yields in a consecutive three-component insertion Sonogashira coupling-addition sequence. The selectivity of either series is remarkable and has its origin in the stepwise character of the terminal addition step as shown by extensive computations on the DFT level. All merocyanines display intense absorption bands in solution and the film spectra indicate J-aggregation. While 1-styryleth-2-enylideneindolones show an intense deep red emission in films, 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones are essentially nonemissive in films or in the solid state. TD-DFT computations rationalize the charge-transfer nature of the characteristic broad long-wavelength absorptions bands.

Triflic acid-promoted cycloisomerization of 2-alkynylphenyl isothiocyanates and isocyanates: a novel synthetic method for a variety of indole derivatives

A unique method for synthesis of structurally diverse types of indoles involving a triflic acid-promoted cycloisomerization and a Wagner–Meerwein-type rearrangement is described.