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Ruthenium(II)‐catalyzed synthesis of π‐conjugated fused imidazo[1,5‐a]quinolin‐2‐ium derivatives have been achieved via C−H activation of quinoline‐functionalized NHC (NHC=N‐heterocyclic carbene) and oxidative coupling with internal alkynes. The reaction occurred with high efficiency, broad substrate scope, tolerates a wide range of functional groups and utilized into a gram‐scale. Synthetic applications of the coupled product have been exemplified in the late‐stage derivatization of various highly functionalized scaffolds. Moreover, most of the annulated products exhibit intense fluorescence and have potential applications in optoelectronic devices. Mechanistic studies have provided insights into the spectroscopic characterization of key five‐membered ruthenacycle intermediate and Ru(0) sandwich species. Based on several control experiments, deuterium‐kinetic isotope effect, and thermodynamic activation parameters the mechanistic finding demonstrated that fused imidazo‐[1,5‐a]quinolin‐2‐ium C(2)−H bond cleavage is the rate‐determining step and ruling out the possibility of reductive elimination for controlling the rate of reaction. [ABSTRACT FROM AUTHOR]

A heterogeneous nanocatalyst comprising palladium (Pd/PdO) and iron-(III) oxide (Fe2O3) in the dimension of 1–4 nm was synthesized using sodium-exchanged zeolite-Y or zeolite-NaY [a type of faujasite (FAU) zeolite having an aluminosilicate framework with a general formula of (Na2)3.5[Al7Si17O48]·32H2O] as a support matrix. The catalyst was investigated as a true heterogeneous catalyst for activation of the robust C–Cl bond of aryl chlorides in the Suzuki–Miyaura cross-coupling (SMCC) reaction. The catalyst with very low Pd loading (0.0037 mol %) exhibited high reactivity in the SMCC reaction with various derivatives of aryl chlorides (Ar–Cl). Biaryl products were obtained with up to a 92% yield, high selectivity, and a good turnover number with this Pd/PdO–Fe2O3-Y catalyst. The catalyst exhibited good thermal stability and was highly recyclable. The reaction was found to be reliant on various parameters such as solvent system, temperature, time, and catalyst amount. A small aliquot of water (H2O) mixed with methanol (CH3OH) dramatically brought a substantial improvement in the product yield of the desired biaryl product. The role of zeolite-NaY was also investigated by comparing the results with various other synthesized catalysts. Different experimental studies indicated that the surface hydroxyl (−OH) groups of zeolite-NaY, modification of basic sites, and the ability to influence the reduction temperature of iron (Fe) and palladium (Pd) influenced the catalytic performance of the synthesized catalyst. The impact of Fe on the electronic structure and reactivity of Pd was analyzed through a density functional theory calculation. This study provided strong evidence for creation of a negative (−ve) charge on Pd with an increasing amount of Fe content and thereby favored the in situ transformation of Pd-(II) to Pd(0) as required in the activation of the C–Cl bond. [ABSTRACT FROM AUTHOR]

Herein, an efficient and expedient method was developed for α‐alkylation of aromatic ketones with secondary alcohols to produce β‐disubstituted ketones using phosphine‐free pincer ruthenium complexes as the catalyst. Single α‐alkylated ketone is produced in high yields even in reactions where a mixture of products is possible. Interestingly, challenging substrates such as unsubstituted and nonhindered acetophenone compounds are effectively alkylated under the reaction conditions. The scope of the reaction can span with a verities of aliphatic, cyclic, and acyclic secondary alcohols. Functionalization of a cholesterol molecule is also possible under the reaction conditions. Substitution on cyclohexyl ring afforded products as a mixture of diastereoisomers, wherein the major isomer is found as 1,4‐cis conformation of the cyclohexyl ring. Origin of the cis stereoselectivity in the alkylation process was explored by DFT calculation study. Mechanistic studies reveal that the dehydrogenation of alcohols follows a proton shuttle‐type of TS, involvement of cross‐aldol condensation and borrowing hydrogen catalysis. Notably, this selective, catalytic C−C bond forming reaction proceeds with low catalyst load, catalytic amount of base under air and produces H2O as the only byproduct, making the process environmentally benign and atom efficient. [ABSTRACT FROM AUTHOR]

Ru(II)-catalyzed, carboxylic acid-assisted oxidative annulation of N -aryl azoles with alkynes via double C-H activation to produce highly functionalized π-extended imidazo[1,2- a ]quinolines is reported. The reaction features a broad substrate generality and tolerates various biologically relevant scaffolds. Interestingly, annulated products showed strong fluorescence properties and an AgIE effect and exhibited a selective fluorescent response toward the Cu 2+ ion. Further photocatalytic properties of the product are demonstrated in the photochemical coupling of azoles and arenes.

The ruthenium/O 2 -catalyzed oxidative annulation reaction of imidazo[1,5- a ]quinolin-2-ium salts with alkynes via N -heterocyclic carbene-directed C-H activation to obtain π-conjugated fused imidazo[1,5- a ]quinolin-2-ium derivatives is reported. Molecular oxygen has been explored as an economic and clean oxidant and an alternative to metal oxidants. The current protocol exhibits a wide range of substrate scope including bioactive (±)-α-tocopherol derivatives. Moreover, most of the annulated products show strong fluorescence properties, indicating their potential for making new light-emitting materials.