(9H-Fluoren-9-ylidene)fluoromethyllithium, a Stabilized Fluoroalkenyl Carbanion. Preparation, Reactions, 13C and 19F NMR Spectra

(9 H -Fluoren-9-ylidene)fluoromethyllithium ( 1 ) was prepared by a low-temperature transmetallation of bromo(9 H -fluoren-9-ylidene)fluoromethane ( 2 ). Whereas the synthesis of unlabeled bromofluoroalkene 2a was based on Wittig-Horner reaction of fluorenone ( 3 ) with ethyl (diethoxyphosphoryl)fluoroacetate ( 4 ), (1- 13 C)-labeled compound 2b was obtained via an addition of labeled lithium 1-ethoxy-2-fluoro(2- 13 C)ethen-1-olate ( 5 ) to ketone 3 . Fluoroethenyllithium 1 was found by a low-temperature 19 F NMR spectroscopy to be stable up to -40 °C; it was reacted with the series of electrophiles, e.g. benzaldehyde ( 6 ), methyl iodide ( 7 ) or chloro(trimethyl)silane ( 8 ). 13 C NMR experiments with (1- 13 C)-labeled 1a proved that fluorocarbenoid 1 is probably monomeric in THF solution in analogy to other halocarbenoids.