Synthesis of Substituted Oxazoles by Visible-Light Photocatalysis

Abstract

A simple and practical method for the synthesis of substituted oxazoles has been developed using readily available α-bromoketones and benzylamines by visible-light photocatalysis at room temperature. The process, which requires 1 mol % of [Ru(bpy)3]Cl2 photocatalyst with K3PO4 and CCl3Br, is effective for accessing a variety of valuable oxazole compounds. The synthetic utility of our protocol was also demonstrated by preparing a natural product, texaline.

Photocascade Catalysis: A New Strategy for Cascade Reactions

“…Quite recently, by taking advantage of [Ru(bpy) 3 ]Cl 2 as a photocatalyst and CCl 3 Br as a terminal oxidant under blue LED irradiation, Cho and co‐workers reported a visible‐light photocascade catalytic method for the synthesis of various biologically and synthetically useful 2,5‐disubstituted and 2,4,5‐trisubstituted oxazoles with moderate to excellent yields (Scheme ) . This methodology was also successfully applied to a gramscale synthesis of bioactive natural product texaline with good yield.…”

Divergent Palladium‐Catalyzed Tandem Reaction of Cyanomethyl Benzoates with Arylboronic Acids: Synthesis of Oxazoles and Isocoumarins

“…Inspired by our recent studies on palladium-catalyzed tandem reactions of o-cyanobiaryls with arylboronic acids for the synthesis of seven-membered 5H-dibenzo[c,e]azepines (Scheme 1b), [10] we envisaged that the palladiumcatalyzed addition of arylboronic acids to cyanomethyl 2-halogenated benzoates and sequential intramolecular Buchwald-Hartwig coupling cyclization would offer a new strategy for the synthesis of 2-arylbenzo[e] [1,4] oxazepin-5-ones (Scheme 1c, proposed transforma-tion). To our surprise, substitution at the 2-position of cyanomethyl benzoates was found to be crucial for the selective synthesis of five-membered oxazoles [11] and six-membered isocoumarins [12] (Scheme 1c, observed transformation). Herein, we report the unexpected discovery using this novel protocol that cyanomethyl benzoates afford 2,4-diaryloxazoles as the sole prod-ucts, while 2-benzoyl-substituted cyanomethyl benzoates deliver a new class of 3-benzoyl-4-aryl-isocoumarins that are often difficult to prepare using traditional routes.…”

Iodine-Catalyzed Functionalization of Primary Aliphatic Amines to Oxazoles, 1,4-Oxazines, and Oxazinones

“…62 The widespread application of the heterocycles led to the development of several synthetic strategies such as Cu II -catalyzed oxidative cyclization, 63 [2 + 2 + 1] annulation of alkyne and nitrile, 64 dehydrogenative annulation, 65 Pd II -catalyzed annulation of amides, 66 and photocatalytic Ru catalysis. 67 The importance of metal-free synthesis was also realized using organocatalysis, 68 cyclization of aminoacids, 69 PhIO-TfOH, 70 and dehydrogenative I 2 -TBHP cyclization. 71 1,4-Oxazines have shown immense importance in biological and material sciences.…”