Photoinduced molecular rearrangements. The photochemistry of 1,2,4-oxadiazoles in the presence of sulphur nucleophiles. Synthesis of 1,2,4-thiadiazoles

✍ Scribed by Nicolò Vivona; Silvestre Buscemi; Stefano Asta; Tullio Caronna

• Publisher: Elsevier Science
• Year: 1997
• Tongue: French
• Weight: 417 KB
• Volume: 53
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(97)00784-9

✦ Synopsis

The photochemistry of some 1,2,4-oxadiazoles in the presence of sulphur nucleophiles has been investigated. Irradiation of the 5-amino-3-phenyl-and 3,5-diphenyl-l,2,4-oxadiazole at X = 254 nm in methanol in the presence of sodium hydrogen sulphide or thiols gave a photo-induced redox reaction at the ring O-N bond, leading to the corresponding N-substituted benzamidines. By contrast, irradiation of the 5-amino-3-phenyl-l,2,4-oxadiazole in the presence of thioureas or thiocarbamates, essentially gave 3-phenyl-5-substituted 1,2,4-thiadiazoles, which presume an N-S bond formation between the ring-photolytic species and the sulphur nucleophile. In turn, irradiation of the same 5amino-3-phenyl-l,2,4-oxadiazole in the presence of thioamides again afforded the redox reaction; in addition, amounts of 3-phenyl-5-substituted-l,2,4-thiadiazoles were also formed. Some mechanistic considerations are reported, and synthetic methodologies leading to 1,2,4-thiadiazoles are emphasized.