Copper-Catalyzed Transfer Hydrogenation of N-Heteroaromatics with an Oxazaborolidine Complex

Abstract

The first-time use of the oxazaborolidine complex in transfer hydrogenation was accomplished. It was prepared without difficulty from cheap materials: ethanolamine and BH 3 ·THF. A general and efficient method for copper-catalyzed transfer hydrogenation of a variety of N-heteroaromatics with an oxazaborolidine–BH 3 complex under mild reaction conditions afforded the corresponding hydrogenated products in up to 96% yield. Mechanistic studies indicate that the hydrogen source originated from water and borane that coordinate with the nitrogen atom of oxazaborolidine. Accordingly, a plausible mechanism for this reaction was proposed. This method was successfully used in the key step synthesis of natural products (±)-angustureine and (±)-galipinine in three steps.

NHC-Palladium(II) Mononuclear and Binuclear Complexes Containing Phenylene-Bridged Bis(thione) Ligands: Synthesis, Characterization, and Catalytic Activities

“…1,2,3,4-Tetrahydroquinoline and its derivatives are known for their importance as synthetically valuable intermediates for pharmaceuticals and agrochemicals. , Catalytic hydrogenation of quinoline is highly atom economical, and heterogeneous palladium catalyst systems are commonly used for the hydrogenation of quinoline. − In this work, ammonia–borane (NH 3 ·BH 3 , AB) as an environmentally benign transfer hydrogenation source substituting the flammable hydrogen for hydrogenation of quinoline was used, , in conjunction with our synthesized palladium catalyst complex. To our knowledge, this homogeneous catalytic system is relatively unexplored. − Thus, we examined the catalytic activity of the palladium complexes for transfer hydrogenation of quinolines beginning with quinoline and AB to screen for optimal reaction conditions.…”

Heterogeneous Hydrogenation of Quinoline Derivatives Effected by a Granular Cobalt Catalyst

“…In a similar vein, simple Cu(ClO4)2 facilitates the reduction of the given N-heterocycle applying the oxazaborolidine complex. 15 By contrast, transfer hydrogenation strategies that rely on precious metals utilize Ru, 16 Rh, 17 or Ir 18 coordination compounds as catalysts.…”

“…Further on, we anticipated that the use of surfactants as emulsifying agents 46 would expedite the catalytic transformation since these compounds are supposed to increase the materials exchange between the gas phase and the liquid portion of the reaction mixture. In fact, however, our approaches employing sodium dodecyl sulfate (SDS), polyethylene glycol (PEG), and a commercial detergent failed to improve the catalyst activity (Table S1, entries [15][16][17].…”

Construction of Functional Superhydrophobic Biochars as Hydrogen Transfer Catalysts for Dehydrogenation of N-Heterocycles

“…Generally, nitrogen-containing heteroarene motifs, which play an important role in a variety of industrial processes, including the pharmacy, dye, pesticide and so forth, due to their chemical, biological, and pharmaceutical properties. − Therefore, synthesis of heteroarenes has garnered significant attention during the past few decades. − Among other synthetic strategies, dehydrogenative transformation of the corresponding saturated N -heterocycles is considered to be one of the most promising and simplest protocols to obtain heteroarenes, which have been successfully achieved by several kinds of catalysts, , including noble-metal or non-noble-metal complexes, such as Ir, − Ru, , Fe, , Rh, , Pd, − Cu, , Co, − etc., in the presence or absence of an acceptor. Especially, single-atom-based heterogeneous catalysts, such as ISAS-Co/OPNC (single Co atomic site catalyst on ordered porous N-doped carbon materials), showed highly efficient catalytic activities not only for dehydrogenation of N -heterocycles to release H 2 but also for the inverse transformation hydrogenation of quinoline to achieve hydrogen storage .…”