Facile and efficient one-pot synthesis of 2-arylbenzoxazoles using hydrogen tetrachloroaurate as catalyst under oxygen atmosphere

Abstract

Abstract:In this paper, we presented a novel method for the facile and efficient one-pot synthesis of 2-arylbenzoxazoles, which were directly synthesized from 2-aminophenol and aldehydes catalyzed by hydrogen tetrachloroaurate (HAuCl 4 ·4H 2 O) under an oxygen atmosphere with anhydrous tetrahydrofuran (THF) as solvent or in solvent-free condition. The results show that this method could bring excellent yields as high as 96%. THF was proven to be the best choice among several solvents screened and the reaction was tolerated with a variety of aromatic aldehydes possessing electron-donating or withdrawing groups. The advantages of the present method lie in catalytic process using economic and environmentally benign dioxygen as oxidant.

Biocidal Activity of Aminomethyl Derivatives of 2-Mercaptobenzoxazole

“…Benzoxazole derivatives, both natural and synthetic, have a wide range of biological activity [4]. Namely, they exhibit antibacterial [5], anti-inflammatory [6], antiviral [7], anti-allergic [8], antifungal [9,10], anthelmintic [11] properties and are inhibitors of cyclooxygenase-2 [12]. The benzoxazole moiety is a constituent of flunoxaprofen, a nonsteroidal anti-inflammatory drug.…”

Benzoxazole and Benzothiazole Synthesis from Carboxylic Acids in Solution and on Resin by Using Ethyl 2‐Cyano‐2‐(2‐nitrobenzenesulfonyloxyimino)acetate and para‐Toluenesulfonic Acid

“…For example, the synthesis of benzothiazole from carboxylic acid in the presence of polyphosphoric acid under reflux conditions at 220 °C has been reported . Various oxidants are used for the synthesis of benzoxazole from 2‐aminophenol and aldehydes, such as Mn(OAc) 3 , DDQ (2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone), PhI(OAc) 2 , ThClO 4 , NiO 2 , BaMnO 4 , Pb(OAc) 4 , and HAuCl 4 ⋅ 4 H 2 O . Recently, the cyclization of 2‐aminothiophenols with alkyl amines by using elemental sulfur at 110–150 °C, or with aryl ketones by using PhCl/DMSO/O 2 at 140 °C, along with the direct cyclization of o ‐haloanilide by using K 2 CO 3 /DMSO at 140 °C, and the cyclization of 2‐halonitrobenzene in the presence of elemental sulfur and benzylamine in pyridine at 100 °C have also been reported.…”

Magnetically recoverable and reusable CuFe2O4nanoparticle-catalyzed synthesis of benzoxazoles, benzothiazoles and benzimidazoles using dioxygen as oxidant

“…Using o-substituted aminoaromatics and aldehyde as the starting materials to construct these heterocycles have caught considerable attention (Scheme 1c). In this regard, several examples of aerobic oxidation pathways have been reported with various transition metal salts or oxidants, such as ZrOCl 2 $8H 2 O, 12 Pd(OAc) 2 /O 2 , 13 CuCl 2 , 14 Sc(OTf) 3 , 15 Yb(OTf) 3 , 16 FeCl 3 $6H 2 O, 17 HAuCl 4 $4H 2 O/O 2 , 18 DDQ, 19 PhI(OAc) 2 , 20 H 2 O 2 -HCl, 21 TEMPO, 22 activated carbon 23 and cyanide. 24 However, in some cases, most of these methods might suffer from some drawbacks such as undesirable stoichiometric oxidants, noble transition metal catalyst, long reaction times, toxic reaction reagents, and residual metal catalysts in the end products, which should still impede their applications for the heterocycle synthesis on a large scale.…”