Competing Ring-Photoisomerization Pathways in the 1,2,4-Oxadiazole Series. An Unprecedented Ring-Degenerate Photoisomerization

• Published in: Journal of organic chemistry Vol. 67; no. 17; pp. 6253 - 6255
• Main Authors: Buscemi, Silvestre, Pace, Andrea, Pibiri, Ivana, Vivona, Nicolò
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 23-08-2002
• Subjects: Chemistry; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with n hetero atom and also o and/or s, se, te hetero atoms; Organic chemistry; Preparations and properties; Amine; Cyclization; Isomerization; Reaction mechanism; Oxadiazole derivatives; Ring contraction; Aromatic compound; Photochemical reaction; Chemical synthesis; Ring expansion; Oxygen nitrogen heterocycle; Methanol
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo025934f

The irradiation of some 5-alkyl-3-amino-1,2,4-oxadiazoles at λ = 254 nm in methanol in the presence of triethylamine (TEA) gave ring-photoisomerization both into 2-alkyl-5-amino-1,3,4-oxadiazoles and, unprecedently, into the ring-degenerate 3-alkyl-5-amino-1,2,4-oxadiazoles. The competing ring contraction−ring expansion route and the internal cyclization−isomerization mechanism explain the results.