An efficient synthesis of 2-aryl(heteroaryl)benzo[d]oxazoles via PIFA-mediated oxidative cyclization of phenolic azomethines

The synthesis of 2-aryl(heteroaryl)benzo[d]oxazoles via intramolecular oxidative cyclization of appropriate phenolic azomethines, is presented, utilizing [bis(trifluoroacetoxy)iodo]benzene (PIFA) as a mild and efficient hypervalent iodine(III) reagent. The reactions are run from 0 °C to ambient temperature and give high yields, 80%–95%, of pure products. The method works efficiently for, 2-arylbenzo[d]oxazoles bearing at position 2, phenyl, 2-hydroxybenzene, 4-trifluoromethylbenzene, 4-fluorobenzene, 3-nitrobenzene, 4-dimethylamino-benzene, naphthalene-1-yl and 4-diphenylamino-benzene substituents, as well as for, 2-heteroaryl-benzo[d]oxazoles bearing at position 2, 1H-pyrrol-2-yl, 1H-imidazol-4-yl and thiophen-3-yl substituents and, disubstituted benzo[d]oxazoles, 2-phenyl-5-nitro, 2-phenyl-5-methyl and 2-phenyl-5-methoxy. Thus, a variety of aromatic electron-donating and electron-withdrawing substituents are well tolerated in this reaction.