... NMR spectra (CDCl, as solvent, chemical shifts in ppm from TMS for 'H NMR, from external TFA for '“F NMR and from external 85% H3P0, for 3'P NMR, pos- itive for downfield shifts) were determined on a Varian EM- 360 (60 MHz ... Journal of Fluorine Chemistry 73 (1995) 161 ...