title: Synthesis of 2-phenyl-4,5-substituted oxazoles by copper-catalyzed intramolecular cyclization of functionalized enamides.
abstract: An efficient two-step synthesis of 2-phenyl-4,5-substituted oxazoles involving intramolecular copper-catalyzed cyclization of highly functionalized novel β-(methylthio)enamides as the key step has been reported. These enamides are obtained by nucleophilic ring-opening of newly synthesized 4-[(methylthio)hetero(aryl)methylene]-2-phenyl-5-oxazolone precursors by alkoxides, amines, amino acid esters and aryl/alkyl Grignard reagents, thus leading to the introduction of an ester, N-substituted carboxamide or acyl functionalities at 4-position of the product oxazoles. Synthesis of two naturally occurring 2,5-diaryloxazoles, i.e., texamine and uguenenazole, via two-step hydrolysis-decarboxylation of the corresponding 2,5-diaryloxazole-4-carboxylates has also been described. Similarly, three of the serine-derived oxazole-4-carboxamides were elaborated to novel trisubstituted 4,2'-bisoxazoles through DAST/DBU-mediated cyclodehydration-dehydrohalogenation sequence. The present protocol is complementary and an improvement to our previously reported silver carbonate-induced cyclization of β-bis(methylthio)enamides to 2-phenyl-5-(methylthio)-4-substituted oxazoles.
authors.affiliation: New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore-560064, Karnataka, India.
authors.forename: S
authors.initials: S
authors.lastname: Vijay Kumar
authors.forename: B
authors.initials: B
authors.lastname: Saraiah
authors.forename: N C
authors.initials: NC
authors.lastname: Misra
authors.forename: H
authors.initials: H
authors.lastname: Ila
mesh_terms: D000577:Amides / Q000737:chemistry*; D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D003500:Cyclization; D010080:Oxazoles / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000577:Amides; D010080:Oxazoles; D003300:Copper