Iron-catalyzed synthesis of benzoxazoles by oxidative coupling/cyclization of phenol derivatives with benzoyl aldehyde oximes

Abstract

An iron-catalyzed oxidative coupling/cyclization reaction for the synthesis of benzoxazoles at room temperature is reported. This reaction was enabled by an inexpensive iron(iii) catalyst by treating readily available phenol derivatives with benzoyl aldehyde oximes. Mechanistic studies show that benzoyl aldehyde oxime is not only used as a substrate, but also serves as an ancillary ligand to support the iron salt in the promotion of the transformation.

Iron and Phenol Co‐Catalysis for Rapid Synthesis of Nitriles under Mild Conditions

“…Initially, we envisioned that the nitrile by‐products in the FeCl 3 ‐catalyzed synthesis of benzoxazoles from benzoyl aldehyde oximes and phenols might just be produced through a Lewis acid‐catalyzed elimination of benzoic acid from the corresponding benzoyl aldehyde oximes . This was proved when we obtained benzonitrile in 32 % yield in the presence of 10 mol‐% of FeCl 3 after 2 h (Table , entry 2), while no product was produced without iron salt and phenol (Table , entry 1).…”

“…However, the reaction required refluxing in toluene for long time (24 h in most cases). [13f] Recently, we reported the iron‐catalyzed synthesis of benzoxazoles from phenols and aldoxime esters, where we noticed the formation of nitriles as by‐product in some cases. With our experience on the reaction, we surmised that it would be possible to obtain nitriles as main products by further exploration of the reaction conditions, thus providing a new access to nitriles from aldoxime esters under mild conditions by using inexpensive and environmentally benign iron catalyst.…”

Iron‐Catalyzed Regioselective Synthesis of 2‐Arylbenzoxazoles and 2‐Arylbenzothiazoles via Alternative Reaction Pathways

“…2‐Phenyl‐5,6‐methylenedioxy‐1,3‐benzoxazole (2e): 2‐Phenyl‐5,6‐methylenedioxy‐1,3‐benzoxazole ( 2e ) was synthesized as described for 2‐phenyl‐5,6‐dimethoxy‐1,3‐benzoxazole ( 2a ) using N ‐(3,4‐methylenedioxyphenyl)benzamide ( 1e ) (0.0513 g, 0.213 mmol) in toluene (1.6 mL) and tetrahydrofuran (0.4 mL). The bromination step was carried out at 40 °C for 3 h and the O ‐arylation step at 130 °C for 20 h. Purification by flash column chromatography (hexane/diethyl ether, 19:1) gave 2‐phenyl‐5,6‐methylenedioxy‐1,3‐benzoxazole ( 2e ) (0.0351 g, 69 %) as a white solid.…”

“…The bromination step was carried out at 40 °C for 3 h and the O ‐arylation step at 130 °C for 20 h. Purification by flash column chromatography (hexane/diethyl ether, 19:1) gave 2‐phenyl‐5,6‐methylenedioxy‐1,3‐benzoxazole ( 2e ) (0.0351 g, 69 %) as a white solid. Mp 142–143 °C (lit . 147–148 °C).…”

C–H Functionalization Strategies in the Naphthalene Series: Site Selections and Functional Diversity

“…79 Although functionalization of naphthols and their derivatives through various methodologies including Friedel-Crafts, dearomatization, oxidative couplings or SET procedures has been reported, such transformations will not be covered in this section. [80][81][82][83][84][85][86][87] Cobalt-promoted monoalkenylation of naphthyl imines using alkenyl phosphates has been described recently by Yoshikai. 88 The procedure is well adapted for the installation of cyclic alkenes (Scheme 22).…”