Abstract
2-Methylthiazole, 2,4,5-trimethylthiazole, 2,4,5-trimethyloxazole, 2-methylbenzothiazole,
and 2-methylbenzoxazole were each reacted with benzoyl chloride in acetonitrile–triethylamine
to generate (Z )-2-(heterocyclic)-1-phenylvinyl benzoates. Base hydrolysis of these vinyl benzoates
formed (Z )-2-(heterocyclic)-1-phenylethenols, which exist in both keto and enol tautomeric
forms. These tautomers were used as starting materials for fused-ring heterocycle
syntheses. Reactions with 2,2-dialkyl-1,3-diacid chlorides in acetonitrile–triethylamine
afforded their corresponding 5,6-ring-fused 8-benzoyl-6,6-dialkyl-6H -thiazolo-, 8-benzoyl-2,3,6,6-tetramethyl-6H -thiazolo-, 8-benzoyl-2,3,6,6-tetramethyl-6H -oxazolo-, 4-benzoyl-2,2-dimethyl-1H -benzo[4,5]thiazolo-, and 4-benzoyl-2,2-dimethyl-1H -benzo[4,5]oxazolo[3,2,-a ]pyridinedione derivatives. The 5,6,6-tri-ring fused species, 10-benzoyl-7,8-dihydropyrano[2,3-d ]thiazolo[3,2-a ]pyridin-5(6H )-one, was formed in the reaction of the tautomers of (Z )-1-phenyl-2-(thiazol-2-yl)ethenol with cyclobutane-1,1-dicarbonyl dichloride via
a ring expansion after 5,6-ring fusion. Functionalized 5,6-ring-fused 8-benzoyl-6H -thiazolo- and 8-benzoyl-6H -oxazolo[3,2-f ]pyrimidine-5,7-diones, and 4-benzoyl-1H -benzo[4,5]thiazolo- and 4-benzoyl-1H -benzo[4,5]oxazolo[3,2-c ]pyrimidine-1,3(2H )-diones were also synthesized by reacting the (Z )-2-(heterocyclic)-1-phenylethenol tautomers with N -chlorocarbonyl isocyanate in THF–triethylamine.
Key words keto-enol tautomers - dielectrophiles - fused-ring heterocycles - nucleophilic attack
- cyclocondensation
