ipso-Substitution of an Acyl group in Reactions of 3-Acyl-substituted Ethyl 7,8-Difluoro-5-oxo-5,9a-dihydropyrazolo[1,5-a]quinoline-4-carboxylates with Electrophilic Reagents

Reactions of 3-acetyl-(benzoyl-) substituted 7,8-difluoro-5-oxo-5,9a-dihydropyrazolo[1,5-a]quinoline-4-carboxylates 1a,b with electrophilic reagents have been studied and reaction of 1a with methyl iodide in dry DMF in the presence of potassium carbonate results in the corresponding 5-methoxy derivative 2, in which the acetyl group at C–3 is easily substituted by a bromine atom. Treatment of 1a,b with bromine causes ipso-substitution of the acetyl (benzoyl) group accompanied by addition of the second bromine atom at position 4; a similar ipso-substitution of the acetyl group at C-3 has been observed on protonation of 1a with sulfuric acid.