Cyclization reactions of tricarbonylmethane thiosemicarbazones: Formation of 1,3,4-thiadiazole derivatives with concomitant CC bond cleavage

✍ Scribed by Somogyi, László

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 417 KB
• Volume: 1995
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.1995199504107

✦ Synopsis

Under acylating conditions 3-acetyl-4-hydroxy-2H-pyran-2one thiosemicarbazones (la, b and 2a, b) are transformed into 2-(acylamino)-5-methyl-1,3,4-thiadiazoles 3b, c, e, f and 2H-pyran-2-ones l c and 2 c via C-C bond cleavage. Similarly, the reaction of lb with RC02H/EtOH (R = Me, Et) af-fords 2-anilino-5-methyl-l,3,4-thiadiazole (3d) and triacetic acid lactone lc. Upon treatment with Ac20/Et3N the dehydroacetic acid derivative lb is transformed into the thiadiazoline 4, while the benzo derivative 2b is converted into thiadiazole 3e and 4-acetoxycoumarin (2c). d e f

Ac

Numerous tricarbonylmethane derivatives, antibiotics, and certain synthetic analogs (often obtained by treatment of B-dicarbonyl compounds with acylating agents) have been shown to display biological activity. (Thi0)acylhydrazones of tricarbonylmethane compounds have also been considered to be potential pharmaceuticals. Recently, we have reported on the synthesis of 1,3,4-thiadiazolylcoumarin derivatives['] by dehydrocyclization of the corresponding thiosemicarbazones 2e, f carrying a lactone moiety in P-position to the C=N-NH group under acetylating conditions commonly used for such transformations.