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

Abstract

(9H-Fluoren-9-ylidene)fluoromethyllithium (1) was prepared by a low-temperature transmetallation of bromo(9H-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), (1-13C)-labeled compound 2b was obtained via an addition of labeled lithium 1-ethoxy-2-fluoro(2-13C)ethen-1-olate (5) to ketone 3. Fluoroethenyllithium 1 was found by a low-temperature 19F 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). 13C NMR experiments with (1-13C)-labeled 1a proved that fluorocarbenoid 1 is probably monomeric in THF solution in analogy to other halocarbenoids.