Synthesis and Comparison of the Reactivity of Allyl Fluorides and ...

5.2.6 Reactions of Difluoroallylic Products with Palladium (0)
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Chapter Five
Having synthesised a small library of allylic difluorides, analogous to the allylic fluorides
synthesised in Chapter Two, further reactions were conducted in order to establish whether
these allylic difluorides and the starting material, 3-bromo-3,3-difluoropropene could
oxidatively add to Pd(0) complexes.
In Chapter Three, C-F activation of allylic fluorides was observed with Pd(0) in the
presence of PPh3, these Pd cationic complexes were successfully reacted with nucleophiles
in Chapter Four giving rise to a non-fluorinated product. Therefore, activation of an allylic
difluoride by Pd(0), followed by subsequent reaction with a nucleophile could lead to
fluoroalkenes (Scheme 5.15).
Scheme 5.15 Proposed reaction scheme
Therefore, the oxidative addition of the allylic difluorides with Pd(0) was conducted by
reacting 2,2-difluorobut-3-enyl benzoate with Pd(dba)2 and PPh3 in CDCl3, the reaction was
monitored by 1 H and 19 F NMR spectroscopy, however, no reaction was observed.
Therefore, the reaction mixture was heated to reflux overnight in order to initiate a reaction,
but with no success.
Scheme 5.16 Reaction of 2,2-difluorobut-3-enyl benzoate with Pd(dba)2
The reaction was repeated but this time with Pd(PPh3)4 as the source of Pd(0), however, this
also only exhibited 2,2-difluorobut-3-enyl benzoate (175) starting material, when analysed
by 1 H and 19 F NMR spectroscopy. Conducting the reaction with Pd(PPh3)4 and the
nucleophile sodium dimethyl malonante also failed to activate the C-F bond and form the
corresponding fluoroalkene. Therefore, these experiments indicate that in Narumi’s Pd
catalysed activation of allylic difluorides, the Ph3SiH is a key component in the activation