3/4‐phenylene bisheterocycles from ring transformation reaction of sydnone derivatives: Synthesis of 3‐[3/4‐heterocyclyl]phenyl‐5‐methyl‐3H‐[1,3,4]‐oxadiazol‐2‐ones from 3/4‐acetylphenylsydnones and their biological properties

The bifunctional 3/4‐acetyl]phenylsydnones 1a, 1b were subjected to a one‐pot ring conversion to 3‐3/4‐acetyl]phenyl‐5‐methyl‐3H‐1,3,4]‐oxadiazol‐2‐ones 2a, 2b , which on further bromination yielded the 3‐3/4‐bromoacyl]phenyl‐5‐methyl‐3H‐1,3,4]‐oxadiazol‐2‐ones 3a, 3b . Reaction of these compounds with thiourea yielded the 3‐3/4‐(2‐aminothiazol‐4‐yl)]phenyl‐5‐methyl‐3H‐1,3,4]‐oxadiazol‐2‐ones 4a, 4b . The other thiazole derivatives 5a, 5b–7a, 7b were prepared by using thiosemicarbazide, thioacetamide, and thiobenzamide, respectively. In another reaction of the bromoacetyl compounds ( 3a, 3b ) with 2‐aminopyridine and 2‐aminothiazole, the fused biheterocyclic compounds 3‐3/4‐imidazo‐1,2‐a]pyridine‐2‐yl]phenyl‐5‐methyl‐3H‐1,3,4]‐oxadiazol‐2‐ones 8a, 8b and 3‐3/4‐imidazo‐2,1‐b]‐thiazol‐6‐yl]phenyl‐5‐methyl‐3H‐1,3,4]‐oxadiazol‐2‐ones 9a, 9b were obtained. The 3‐3/4‐(benzofuran‐2‐carbonyl)]phenyl‐5‐methyl‐3H‐1,3,4]‐oxadiazol‐2‐ones 10a, 10b were obtained by treatment of compounds 3a, 3b with o‐hydroxy benzaldehyde. Most of these compounds exhibited antifungal activity greater than the reference drugs used. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:50–54, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20255