Polyhalogeno-allenes and -acetylenes. Part 15. Dipolar cycloadditions of N-phenylsydnone and aryl azides to perfluoropropadiene and perfluoropropyne

Abstract

N-Phenylsydnone reacts with perfluoropropadiene to give 3-fluoro-1-phenyl-4-trifluoromethylpyrazole (2), anionotropic rearrangement following the dipolar cycloaddition; with perfluoropropyne, giving a 1 : 2 mixture of (2) and the isomeric 4-fluoro-1-phenyl-3-trifluoromethylpyrazole (3); and with perfluorobut-2-yne to give the homologue 1-phenyl-3,4-bis(trifluoromethyl)pyrazole (4). Phenyl azide and perfluoropropadiene react at 50 °C to give a 9 : 1 mixture of 4-fluoro-1-phenyl-5-trifluoromethyl-1,2,3-triazole (5) and 5-fluoro-1-phenyl-4-trifluoromethyl-1,2,3-triazole (6), also by consecutive cycloaddition and anionotropic rearrangement. The minor isomer, believed to be compound (6), was the only adduct isolated by similar treatment of perfluoropropyne. Perfluoropropadiene and pentafluorophenyl azide react slowly to give a low yield of an adduct believed to be 4(or 5)-fluoro-1-pentafluorophenyl-5(or 4)-trifluoromethyl-1,2,3-triazole. The orientations of these additions are discussed in terms of the frontier orbitals involved.