THE INSITU GENERATION AND TRAPPING OF SOME FLUORINE-SUBSTITUTED KETENES

Fluoroketene, difluoroketene, methylfluoroketene, trifluoromethylfluoroketene, and phenylfluoroketene were each generated, in situ, via dehydrohalogenation of the respective acid chlorides. In the presence of cyclopentadiene [2 + 2] adducts were obtained in all but the difluoroketene case. In the absence of cyclopentadiene, low temperature F-19 nmr indicated the presence of acyl ammonium salts and enolates, potential precursors of the ketenes, but no actual ketene species could unambiguously be detected. The stereochemical results were consistent with the currently accepted steric-based mechanistic rationale for stereochemical determination in ketene cycloadditions.