Fluorocarbon derivatives of nitrogen. Part 8. Reactions between heteroaromatic N-imines (N-iminopyridinium and N-iminoquinolinium ylide) and perfluoropropene, 2H-pentafluoropropene, perfluorobut-2-ene, perfluoro-(2-methylpent-2-ene), perfluorobut-2-yne, and perfluoropyridine: synthesis of fluorinated 3-azaindolizines (pyrazolo[1,5-a]pyridines)

Abstract

N-Iminopyridinium ylide reacts with perfluoropropene (or 2H-pentafluoropropene) and perfluorobut-2-ene (or perfluorobut-2-yne) to provide 2-fluoro-3-(trifluoromethyl)pyrazolo[1,5-a]pyridine and 2,3-bis(trifluoromethyl)pyrazolo[1,5-a]pyridine, respectively; oxidation of these products with aqueous potassium permanganate gives the corresponding pyrazolecarboxylic acids. Perfluoro-(2-methylpent-2-ene) is attacked by N-iminopyridinium ylide to produce 2-(pentafluoroethyl)-3,3-bis(trifluoromethyl)-3,3a-dihydropyrazolo[1,5-a]pyridine, which can be converted via thermal treatment with tetracyanoethylene into a mixture of 2-(pentafluoroethyl)-3-(trifluoromethyl)pyrazolo[1,5-a]pyridine and 5-(dicyanomethylene)-2-(pentafluoroethyl)-3,3-bis(trifluoromethyl)-3,5-dihydropyrazolo[1,5-a]pyridine. N-Iminoquinolinium ylide reacts with perfluoropropene, perfluorobut-2-ene, and perfluoropyridine in hot dimethylformamide in the presence of potassium carbonate to yield 2-fluoro-3-(trifluoromethyl)pyrazolo[1,5-a]quinoline, 2,3-bis(trifluoromethyl)pyrazolo[1,5-a]quinoline, and N-(tetrafluoro-4-pyridyl)iminoquinolinium ylide, respectively.