Survey of reactivity of some enolates with pentafluoropyridine and 4-phenylsulfonyl-2,3,5,6-tetrafluoropyridine

Site reactivity of some enolates derived from acetyl attached to the aromatic and heteroaromatic system with pentafluoropyridine and 4-phenylsulfonyl-2,3,5,6-tetrafluoropyridine under basic conditions in dry THF at reflux was investigated. The aromatic nucleophilic substitution of pentafluoropyridine with enolates occurs at the 4-position of pyridine ring by the oxygen site of enolate. In contrast, the reaction of 4-phenylsulfonyl-tetrafluoropyridine with enolates gives corresponding furo[3,2-b]pyridine compound by the first nucleophilic substitution at the 2-position of the pyridine ring by carbon nucleophile site followed by the intramolecular ring closure at the geometrically accessible 3-position of the pyridine ring by oxygen site of enolate.