Palladium-Catalyzed Q-Tube-Assisted Protocol for Synthesizing Diaza-dibenzo[a,e]azulene and Diaza-benzo[a]fluorene Derivatives via O₂ Acid-Promoted Cross-Dehydrogenative Coupling

Abstract

An appropriate and efficient Q-tube-assisted palladium-catalyzed strategy for the synthesis of novel, unparalleled diaza-dibenzo­[a,e]­azulene and diaza-benzo­[a]­fluorene derivatives has been sophisticated, which includes oxygen and AcOH-induced oxidative C­(sp3)–C­(sp2) cross-dehydrogenative coupling reactions of 1-amino-2-imino-4-arylpyridine-3-carbonitriles with benzocyclic ketones such as benzosuberone, tetralone, thiochromone, and chromone, respectively. This Q-tube gas purging kit assisted-protocol features safe due to easy pressing and sealing, a wide substrate scope, easy workup and purifying phases, and the use of O2 as a benign oxidant, in addition to being scalable and having a high atom economy. The suggested mechanistic pathway includes a formal dehydrative step followed by palladium AcOH-induced CH(sp3)–CH(sp2) oxidative cross-coupling. In this study, X-ray crystallographic analysis has been used to authenticate the targeted products.

The Q-Tube-Assisted Green Sustainable Synthesis of Fused Azines: New Synthetic Opportunities via Innovative Green Technology

“…Bearing in mind all of the above and inspired by our previous work utilizing green chemistry tools for the synthesis of biologically active heterocyclic compounds [17][18][19][20] and the recently published work on utilizing the high-pressure Q-tube [21][22][23][24][25], we are boiling point is exceeded during the reaction process. The Arrhenius equation states that reaction rates double when the temperature is raised by 10 °C (Equation (1)).…”

Recent Advances in Palladium-Catalyzed Oxidative Couplings in the Synthesis/Functionalization of Cyclic Scaffolds Using Molecular Oxygen as the Sole Oxidant

“…Using a similar strategy, Ibrahim and Behbehani described a route to fused N-heterocycles obtaining novel unparalleled diazadibenzo[a,e]azulenes and diaza-dibenzo[a]fluorenes (Scheme 26). 51 This protocol describes a palladium-catalyzed carboxylic acid-induced synthesis using Q-tube, in which the reaction is conducted at high pressures and under oxygen atmosphere in a The use of epoxides as an alternative to alkylating reagents in coupling reactions was firstly reported by Wang and co-workers in 2021 (Scheme 27). 52 This protocol manages to overcome the preference of formation of Pd-alkoxide from ring opening of the epoxide, favoring these species to attack the amide carbonyl group, and thus leading to a lactonization product, rather than βhydrogen elimination path, which conducts to a different product.…”

High-Pressure Metal-Free Catalyzed One-Pot Two-Component Synthetic Approach for New 5-Arylazopyrazolo[3,4-b]Pyridine Derivatives

“…The Q-tube strategy was recommended as the technique of preference for the cleanest, shortest, and most effective preparation of the heterocyclic compounds under study [ 22 ]. In other respects, the coupling Q-tube-assisted approach with the one-pot multicomponent reactions (MCRs) strategy is considered to be one of the most advantageous protocols for achieving step efficiency and atom economy [ 19 , 23 , 24 , 25 , 26 ]. In this study, the coupling of the Q-tube-mediated protocol with the two-component reaction (MCR) strategy can be investigated to provide universal access to a series of unreported 5-arylazopyrazolo[3,4- b ]pyridines with superior reaction profiles and higher rates and approximately quantitative yields.…”