Straightforward synthesis of monofluoroalkenes
Alkenes are important intermediates in organic synthesis and the preparation of fluoroalkylidenes is still a remaining challenge. After the presentation of the common approaches reported in the literature, the recent development of the Julia-Kocienski reaction to prepare in one step fluoroalkylidenes is discussed and presented.
Fluoroalkenes have been largely used to prepare new drugs and materials. The main applications cover a large panel of compounds such as pheromones, insecticides, herbicides, peptide mimics, or nucleosides analogs and also monomers, and several examples are reported in two previous reviews (1). However, due to the particular reactivity of fluoroorganic compounds, the synthesis of fluoroalkenes is not straightforward, especially in the case of fluoroalkylidenes. In this short article, we report the main methods developed for the construction of a fluorinated carbon-carbon double bond by using elimination reactions, Wittig and related reactions, Peterson olefination, and finally the modified Julia reaction (also called Julia-Kocienski).
So far, elimination reactions, such as dehydrogenation and dehydration, are the common way to prepare terminal fluoroalkenes (Scheme 1). Dehydration of t-fluoroalcohols in acidic medium has been used first (2, 3) but this approach was quickly limited. Alternatively, leaving group elimination can be realized, after epoxide ring-opening reaction with ...