Highly Ordered Mesoporous Cobalt Oxide as Heterogeneous Catalyst for Aerobic Oxidative Aromatization of N‐Heterocycles

Abstract

N‐heterocycles are key structures for many pharmaceutical intermediates. The synthesis of such units normally is conducted under homogeneous catalytic conditions. Among all methods, aerobic oxidative aromatization is one of the most effective. However, in homogeneous conditions, catalysts are difficult to be recycled. Herein, we report a heterogeneous catalytic strategy with a mesoporous cobalt oxide as catalyst. The developed protocol shows a broad applicability for the synthesis of N‐heterocycles (32 examples, up to 99 % yield), and the catalyst presents high turnover numbers (7.41) in the absence of any additives. Such a heterogenous approach can be easily scaled up. Furthermore, the catalyst can be recycled by simply filtration and be reused for at least six times without obvious deactivation. Comparative studies reveal that the high surface area of mesoporous cobalt oxide plays an important role on the catalytic reactivity. The outstanding recycling capacity makes the catalyst industrially practical and sustainable for the synthesis of diverse N‐heterocycles.

Efficiently Aerobic Dehydrogenation of N‐Heterocycles and Hydrocarbons over MnAl Oxides

“…As shown in Scheme 4, amine radical species 1 a' is firstly generated via electron transfer from nitrogen to Mn 4 + or Mn 3 + combining with the XPS analysis of the MnAlO catalyst (Figure S3). [16] Then, the formed 1 a' underwent a CÀ H abstraction to afford an imine 2 a' intermediate with the formation of molecular H 2 O via proton transfer (PT) and reoxidation of the reduced manganese. [26] Once produced, the isomerization of 2 a' affords 2 a'' and 2 a'''.…”

“…Actually, some progress has been made in the last decade based on Co, [2,[15][16][17] Ni, [18,19] Cu, [20][21][22] Mn, [23][24][25][26] et al Among these non-noble metals, manganese-based catalysts exhibited greater application potential. Mesoporous manganese oxides reported by Suib et al can accomplish the reactions at 130 °C with an air balloon, [23] but the yields of the product are not satisfied, and the preparation procedure of catalyst is complicated.…”

“…Actually, some progress has been made in the last decade based on Co, [2,15–17] Ni, [18,19] Cu, [20–22] Mn, [23–26] et al. Among these non‐noble metals, manganese‐based catalysts exhibited greater application potential.…”

An efficient biocatalytic oxidative dehydroaromatization approach for the construction of quinolines enabled by monoamine oxidase with molecular oxygen

“…Correspondingly, the content of [M + H] + ion at m/z 132.0808 did not decrease (III and IV), implying that PpMAO was responsible for the second-step oxidation. Consequently, according to the mechanism of oxidative dehydroaromatization of THQs in the literature 15,28,30,[39][40][41] and the properties of monoamine oxidase, 42 we proposed a plausible catalytic mechanism for the PpMAO biocatalytic aromatization of 1a (Scheme 2): PpMAO first oxidizes 1a to the imine intermediate 1c, which then tautomerizes into 1d and 1e. Thereafter, 1e undergoes a second dehydrogenation of C-N to give quinoline 1b.…”

General Surface-Casting Synthesis of Mesoporous Metal Oxides with Hollow Structures and Ultrahigh Surface Areas

“…Metal oxides with high surface areas and crystalline framework have attracted a great deal of interest in both the academic and the industrial worlds. − Benefiting from their unique high concentration of exposed surface atoms and fascinating thermal, electronic, optical, and chemical properties, high surface area metal oxides are widely used in catalysis, ,− sensors, − energy storage, and many other areas. , There are normally two methods to create high surface metal oxides. One is to reduce the particle size of the metal oxide, which may lead to the difficulties in handling.…”