Copper‐Catalyzed Aerobic Oxidative C(aryl)OH Bond Functionalization of Catechols with Amines Affording Benzoxazoles

Abstract

Thef irst copper-catalyzed aerobic oxidative C(aryl) À OH bondf unctionalization of catechols is reported.U nder air, at room temperature,i nt he presence of ac opper catalyst, catechols react with amines to produce the corresponding benzoxazoles in high yields.M echanistic studies suggest that the reactionp roceeds via an intriguing competitive oxidation and as ynergetic catalysis between catechol and amine.

Amino Acids: Nontoxic and Cheap Alternatives for Amines for the Synthesis of Benzoxazoles through the Oxidative Functionalization of Catechols

“…Based on the literature reports and our obtained results, we proposed a mechanistic pathway for the synthesis of benzoxazoles via the reaction of amino acids ( 3 ) and 3,5‐di‐ tert ‐butylbenzene‐1,2‐diol ( 1 ) in the presence of NM−Fe 3 O 4 in H 2 O/EtOH 3:1 at reflux temperature (Scheme ). In the first step, oxidation of 3,5‐di‐ tert ‐butylbenzene‐1,2‐dio ( 1 ) catalyzed by NM−Fe 3 O 4 gives the key intermediate ortho ‐quinone ( 5 ), followed by a nucleophilic addition of amino group of amino acids to the less hindered carbonyl group on the meta ‐position of ( 5 ) to generate intermediate ( 6 ).…”

“…The crude products were purified by column chromatography on silica gel to give the pure products. [6] Purified by column chromatography on silica gel and eluted with ethyl acetate/petroleum ether (1:100 4,28.8,29.9,31.9,34.4,35.0,113.9,118.6,133.4,141.4,146.9,147.1,170.7. Anal.…”

“…Brown liquid, 1 14.7,29.9,31.9,34.4,35.0,113.6,118.7,133.4,141.7,147.1. Calcd for C 16 H 23 NO: C,78.32;H,9.45;N,5.71;Found: C,78.14;H,9.62;N,5.83. 7-Di-tert-butylbenzo[d]oxazole (4 c) [6] Purified by column chromatography on silica gel and eluted with ethyl acetate/petroleum ether (1:100 9, 31.8, 34.4, 35.1, 114.6, 119.9, 134.2, 140.3, 147.8, 152.0. Calcd for C 15 H 21 NO: C,77.88;H,9.15;N,6.05;Found: C,77.70;H,9.31; N, 6.19.…”

“…Calcd for C 21 H 32 N 2 O 2 : C,73.22;H,9.36;N,8.13;Found: C,73.41;H,9.19;N,8.33. [7] Purified by column chromatography on silica gel and eluted with ethyl acetate/petroleum ether (1:100 25.77,29.96,30.83,31.83,34.42,35.04,69.20,73.90,114.32,119.42,133.84,141.06,147.11,147.51,165.81. Calcd for C 19 H 27 NO 2 : C,75.71;H,9.03;N,4.65;Found: C,75.69;H,9.30;N,4.83. [6] Purified by column chromatography on silica gel and eluted with ethyl acetate/petroleum ether (1:100). Isolated yield: 93% (0.28 g).…”

“…Brown liquid, 1 9,31.8,34.4,35.0,38.0,114.1,119.1,122.2,123.3,133.6,136.8,141.6,147.3,147.3,149.6,155.4,163.4. Calcd for C 21 H 26 N 2 O: C,78.22;H,8.13;N,8.69;Found: C,78.40;H,7.88;N,8.88. [6] Purified by column chromatography on silica gel and eluted with ethyl acetate/petroleum ether (1:100). Isolated yield: 95% (0.28 g).…”