Metal-Free Oxidative Coupling of Benzylamines to Imines under an Oxygen Atmosphere Promoted Using Salicylic Acid Derivatives as Organocatalysts

Abstract

The oxidative coupling of benzylamines proceeds efficiently using salicylic acid derivatives as organocatalysts under an oxygen atmosphere, affording the corresponding N -benzylidenebenzylamines in high yields. Electron-rich salicylic acid derivatives such as 4,6-dimethoxysalicylic acid and 4,6-dihydroxysalicylic acid exhibit excellent catalytic activities for the oxidative coupling of benzylamines to give the corresponding imines. This amine oxidation can also be applied to the synthesis of nitrogen-containing heterocycles such as benzimidazole derivatives. Furthermore, to recycle the catalyst, silica gel supported with 4.7 wt % of 4,6-dihydroxysalicylic acid is prepared, which acts as a recyclable catalyst, oxidizing benzylamine to imine four times successfully.

Aromatic Dendrimers Bearing 2,4,6-Triphenyl-1,3,5-triazine Cores and Their Photocatalytic Performance

“… 30 − 38 In the recent years there has been a great progress in designing novel photocatalysts dedicated to such oxidation processes. These studies include, e.g., the use of novel BODIPY, 39 , 40 phenoxazine, 41 , 42 or salicylic acid 43 derivatives as effective photocatalysts, also for the aerobic oxidation processes. 39 , 40 …”

Recent Advances in the Synthesis of Benzimidazole Derivatives from the Oxidative Coupling of Primary Amines

“…clocondensation reaction of benzylic amines (1.5 equiv) with o-phenylenediamines (1 equiv), under an oxygen atmosphere (0.1 MPa), in toluene at 110 °C for 12 hours. 32 Diverse substituents on the phenyl group of the benzylamine or on the aromatic ring of the o-phenylenediamine were well tolerated, affording 2-substituted benzimidazole derivatives in high yields ranging from 85 to 95% (Scheme 12). Through additional experiments, the authors demonstrated that the oxidation of benzylamine proceeds following a radical mechanism.…”

Direct synthesis of amides and imines by dehydrogenative homo or cross-coupling of amines and alcohols catalyzed by Cu-MOF

“…[1][2][3] Typically for the synthesis of imines, a mixture of an aldehyde or ketone with an amine in the presence of a catalyst is required. On the other hand, many useful oxidation methods for the synthesis of imines have been developed 4 which include dimerization of primary amines [5][6][7][8][9][10] oxidation of secondary amines [11][12][13][14] and other methodologies. [15][16][17][18][19][20][21][22][23] The formation of amide bonds is one of the most commonly used organic reactions due to the widespread presence of this functional group in natural products, pharmaceutical compounds, and synthetic polymers.…”