FLASH PHOTOLYTIC DECARBONYLATION AND RING-OPENING OF N-(PENTAFLUOROPHENYL)AMINO)-3-PHENYLCYCLOPROPENONE - ISOMERIZATION OF THE RESULTING YNAMINE TO A KETENIMINE, HYDRATION OF THE KETENIMINE, AND HYDROLYSIS OF THE ENAMINE PRODUCED BY RING-OPENING

Flash photolysis of -(pentafluorophenyl)amino)-3-phenylcyclopropenone, 4, in aqueous solution was found to produce N-(pentafluorophenyl)phen ylethynamine, 3, by the expected photodecarbonylation reaction and als o 2-phenyl-3-(N-(pentafluorophenyl)amino)acrylic acid, 5, by an appare ntly unprecedented photochemical ring-opening process. The ynamine und erwent rapid isomerization to N-(pentafluorophenyl)phenylketenimine, 9 , by an acid-catalyzed route that involves rate-determining proton tra nsfer to the beta-carbon atom of the ynamine and also by a base-cataly zed route involving equilibrium ionization of the N-H bond of the ynam ine to give an ynamide ion followed by rate-determining beta-carbon pr otonation of this ion. Saturation of the base catalysis allowed determ ination of the acidity constant of the ynamine; the result, pQ(a) = 10 .23, makes this amine a remarkably strong nitrogen acid. Hydration of the ketenimine 9 gave N-(pentafluorophenyl)phenylacetamide, 6, as the ultimate product produced by this reaction route, and hydrolysis of th e aminoacrylic acid 5 gave pentafluoroaniline, 7, and 2-phenylformylac etic acid, 10, which underwent decarboxylation to phenylacetaldehyde, 8, as the ultimate products of this route.