Microwave-Assisted One-Pot Synthesis of Diverse Tribenzo[a,f,h]azulen-10-ones

Azulene-type polycyclic hydrocarbons have recently attracted a great deal of attention from researchers; however, their structure-property correlations and possible uses are not being fully explored due to the lack of effective synthesis techniques. Herein, we report a hitherto unexplored one-pot, microwave-assisted synthetic strategy toward diverse tribenzo[a,f,h]azulen-10-ones by tandem Suzuki coupling and a subsequent cyclo-condensation process. The strategy provides tribenzo[a,f,h]azulen-10-ones in good to excellent yields with structural versatility, including thiophene-embedded tribenzo[a,f,h]azulen-10-ones. In addition, UV-visible absorption studies have been used to investigate their structural and photophysical properties. This strategy offers a new platform for promptly synthesizing numerous unexplored azulenone units.

Meyer-Schuster rearrangement/allylic alkenylation of propynolaldehydes with olefins to synthesize skipped 1,4-dienes

A highly efficient method for the straightforward synthesis of skipped 1,4-dienes is presented via p-TsOH·H2O-catalyzed intramolecular intercepted Meyer-Schuster rearrangement/allylic alkenylation of propynolaldehydes with olefins in a one-pot manner. This cascade transformation is characterized by metal-free and mild conditions, extensive substrate applicability, atom economy, gram-scale production, and water as the sole by-product. Furthermore, the resulting functionalized 1,4-dienes could be derivatized by Fe(III)-promoted radical cyclization, allylic methoxylation under reductive conditions, and Pd(II)-catalyzed Sonogashira coupling.

Phosphinylation/cyclization of propynolaldehydes to isobenzo-furanylic phosphine oxides displaying AIE properties

Investigating organic reactions to synthesize novel molecules that exhibit aggregation-induced emission (AIE) characteristics is becoming a research hotspot. Herein, we develop a one-pot phosphinylation/cyclization reaction between propynolaldehydes and diarylphosphine oxides to generate isobenzofuran-substituted phosphine oxides (IBFPOs) displaying AIE properties. Such a reaction possesses benefits such as metal-free synthesis, simple operation and wide substrate applicability. Further structural modifications of the products have been implemented through the palladium-catalyzed Sonogashira reaction, Ullmann coupling and Diels-Alder addition. Furthermore, these AIE luminogens (AIEgens), which have satisfactory quantum yields and tunable emission covering the entire visible region, can be employed for the cell imaging of lipid droplets in HeLa cells. Notably, quantitative evaluation of the phototherapy effect demonstrates that one of these presented AIEgens, namely IBFPO-3j, displays high type-I reactive oxygen species (ROS) generation efficiency, enabling its effective application in photodynamic therapy in a hypoxic environment.

Brønsted Acid-Catalyzed Intramolecular Tandem Double Cyclization of γ-Hydroxy Acetylenic Ketones with Alkynes into Naphtho[1,2-b]furan-3-ones

A metal-free and atom-economic route for the synthesis of naphtho[1,2-b]furan-3-ones has been realized via p-TsOH·H2O-catalyzed intramolecular tandem double cyclization of γ-hydroxy acetylenic ketones with alkynes in formic acid. The benzene-linked furanonyl-ynes are the key intermediates obtained by the scission/recombination of C-O double bonds. Further, the structural modifications of the representative product were implemented by reduction, demethylation, substitution, and [5 + 2]-cycloaddition.

Synthesis of metalla-dual-azulenes with fluoride ion recognition properties

Azulene-based conjugated systems are of great interests due to their unusual structures and photophysical properties. Incorporation of a transition metal into azulene skeleton presents an intriguing opportunity to combine the dπ-pπ and pπ-pπ conjugated properties. No such metallaazulene skeleton however has been reported to date. Here, we describe our development of an efficient [5 + 2] annulation reaction to rapid construction of a unique metal-containing [5-5-7] scaffold, termed metalla-dual-azulene (MDA), which includes a metallaazulene and a metal-free organic azulene intertwined by sharing the tropylium motif. The two azulene motifs in MDA exhibit distinct reactivities. The azulene motif readily undergoes nucleophilic addition, leading to N-, O- and S-substituted cycloheptanetrienyl species. Demetalation of the metallaazulene moiety occurs when it reacts with nBu4NF, which enables highly selective recognition of fluoride anion and a noticeable color change. The practical [5 + 2] annulation methodology, facile functional-group modification, high and selective fluoride detection make this new π-conjugated polycyclic system very suitable for potential applications in photoelectric and sensing materials.

Dual Proton/Silver-Catalyzed Serial (5 + 2)-Cycloaddition and Nazarov Cyclization of (E)-2-Arylidene-3-hydroxyindanones with Conjugated Eneynes: Synthesis of Indanone-Fused Benzo[cd]azulenes

A one-pot step-economic tandem process involving (5 + 2)-cycloaddition and Nazarov cyclization reactions has been reported for the facile synthesis of indanone-fused benzo[cd]azulenes from (E)-2-arylidene-3-hydroxyindanones and conjugated eneynes. This highly regio- and stereoselective bisannulation reaction is enabled by dual silver and Brønsted acid catalysis and opens up a new avenue for the construction of important bicyclo[5.3.0]decane skeletons.

Annulations involving 1-indanones to access fused- and spiro frameworks

Indanones are prominent motifs found in number of natural products and pharmaceuticals. Particularly, 1-indanones occupy important niche in chemical landscape due to their easy accessibility and versatile reactivity. In the past few years, significant advancement has been achieved regarding cyclization of 1-indanone core. The present review focuses on recent (2016-2022) annulations involving 1-indanones for the construction of fused- and spirocyclic frameworks. In this context, new strategies for synthesis of various carbocyclic as well as heterocyclic skeletons are demonstrated. Mechanistic aspects of representative reactions are illustrated for better understanding of reaction pathways. A large number of transformations described in this review offer stereoselective formation of desired polycyclic compounds. Importantly, several reactions provide biologically relevant compounds and natural products, such as, plecarpenene/plecarpenone, swinhoeisterol A, cephanolides A-D, diptoindonesin G and atlanticone C.

Metal-Free Intramolecular [3+2] Cycloaddition of γ-Hydroxy Acetylenic Ketones with Alkynes for the Synthesis of Naphtho[1,2-c]furan-5-ones and Its Derivatization via a Selective C(sp2)-H Deuteration Reaction

A metal-free intramolecular [3+2] cycloaddtion has been achieved by treating benzene-linked propynol-ynes with AcOH/H₂O in a one-pot manner. The reaction provides greener, 100% atom-economic, highly regioselective, and more practical access to functionalized naphtho[1,2-c]furan-5-ones with valuable and versatile applications. The regioselective α-deuteration of naphtho[1,2-c]furan-5-ones has been also presented with excellent deuterium incorporation and chemical yields. Moreover, the fluorescent properties of naphtho[1,2-c]furan-5-one products have been investigated in solution.