3/4-phenylene bisheterocycles from ring transformation reaction of sydnone derivatives: Synthesis of 3-3/4-heterocyclylphenyl-5-methyl-3H-1,3,4-oxadiazol-2-ones from 3/4-acetylphenylsydnones and their biological properties

The bifunctional 3/4-acetylphenylsydnones 1a, 1b were subjected to a one-pot ring conversion to 3-3/4-acetylphenyl-5-methyl-3H-1,3,4-oxadiazol-2-ones 2a, 2b, which on further bromination yielded the 3-3/4-bromoacylphenyl-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.2025