Acceptorless Dehydrogenative Cyclization of o‐Aminobenzylamines and Aldehydes to Quinazolines in Water Catalyzed by a Water‐Soluble Metal‐Ligand Bifunctional Catalyst

Abstract

The construction of quinazolines via acceptorless dehydrogenative cyclization of o-aminobenzylamines and aldehydes in water has been accomplished. In the presence of a watersoluble metal-ligand bifunctional catalyst [Cp*Ir(6, 6'-(OH) 2 bpy)(H 2 O)][OTf] 2 (2 mol %), reactions were carried out at 130 8C for 12 h in water to afford the desired products in 52-83 % yields. Apparently, OH units in the bpy ligand are crucially important for the enhancement of the catalytic activity. The liberation of hydrogen gas in the process of the cyclization was also confirmed. The protocol is highly attractive because of high atom efficiency and environmental friendliness. Notably, this research would facilitate the progress of acceptorless dehydrogenative reactions in water.

A Visible‐Light Promoted Amine Oxidation Catalyzed by a Cp*Ir Complex

“…For example, tetrahydroharmine, harmaline, and harmine, are all naturally occurring N ‐heterocyclic alkaloids sharing the β‐carboline structure, differing only in their degree of saturation but displaying different pharmacological properties [23] . MAO selectively catalyzes only the first oxidation step, whereas CAD generally results in the fully perdehydrogenated product [5–22] …”

“…CAD requires no external sacrificial oxidant and releases dihydrogen as sole by-product. Although great progress has been achieved, [11][12][13][14][15][16][17][18] most of the CADs are carried out in organic solvent or under strongly alkaline conditions at high temperature. Noteworthy exceptions include work by Li [19] and Kanai's [20,21] tandem catalysis as well as Crabtree's [22] electrocatalysis.…”

“…[23] MAO selectively catalyzes only the first oxidation step, whereas CAD generally results in the fully perdehydrogenated product. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] From the viewpoint of sustainable chemistry, a synthetic catalyst working in water under mild conditions is in high demand to reduce its environmental impact. [24] Moreover, such a synthetic catalyst is also applicable to chemoenzymatic multistep transformation enabled by concurrent use of synthetic catalysts and enzymes.…”

Transition-metal-catalyzed synthesis of quinazolines: A review

“…In the presence of the [Cp*Ir (6, 2 bpy)(H 2 O)][OTf] 2 catalyst, the ADC reaction between 2aminobenzyl amines 14a and benzaldehydes 9c at 130 °C for 12 h in water afforded quinazolines 150 in 52%-83% yields via ligandpromoted dehydrogenation (Scheme 22B). (Fan et al, 2017) Furthermore, electron-donating and electron-withdrawing groups on the aromatic ring and aliphatic aldehydes resulted in the corresponding products 150 in good yields. The attractive benefits of this environmentally benign approach include high atom efficiency and being oxidant-and organic solvent-free.…”

Iridium-Catalyzed Acceptorless Dehydrogenative Coupling of 2-Aminoarylmethanols with Amides or Nitriles to Synthesize Quinazolines

“…For instance, the groups of Balaraman (Scheme 1a) 16 and Srimani (Scheme 1b) 17 reported a manganesecatalyzed ADC reaction of amines for direct synthesis of Nheterocycles with alcohols. Meanwhile, Ru-catalyzed (Scheme 1a and 1c), 18 iridium-catalyzed (Scheme 1b), 19 and Ni-catalyzed (Scheme 1a) 20 ADC reaction were also explored for the synthesis of quinazolines. In addition, the cheap metal such as Fe was also served as catalyst for the ADC reaction to construct quinazolines.…”