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

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Chapter Three
when the reaction was conducted in THF and toluene at – 78 ºC for 1 hour and then warmed
over 24 hours to room temperature (entries 4 and 5).
Conducting the reaction using equimolar amounts of allylic fluoride and Pd(dba)2 in toluene
at room temperature and with heating also resulted in starting material (entries 6 and 7).
However, it was found that when Pd(PPh3)4 was used and the reaction mixture was stirred at
– 78 ºC for 1 hour, a precipitate clearly formed (entry 8). Analysis by 1 H and 19 F NMR
spectroscopy in MeOD revealed that the starting allylic fluoride was no longer present and
there were peaks that could be attributed to the formation of a �-allyl palladium species.
Further analysis by 2-D 1 H- 1 H COSY NMR exhibited that the allylic peaks were coupling to
each other as seen in the �-allyl palladium complexes synthesised from allylic chlorides. In
the 19 F NMR spectrum a very broad peak was observed at -171.5 ppm, the identity of which
is unclear, although it was postulated that fluoride may have reacted with the glass of the
NMR tube. The reaction solvent, which was removed from the precipitate, was also
analysed by 1 H and 19 F NMR spectroscopy and was found to contain unreacted starting
material and triphenylphosphine. The mixture also readily formed crystals and X-ray
crystallography determined triphenylphosphine oxide also to be present.
Scheme 3.15 Reaction of 2-fluorobut-3-enyl benzoate with Pd(PPh3)4
The same reaction conditions were used with 2-(2-fluorobut-3-enyl)isoindoline-1,3-dione
(74) (entry 10). After removal of the reaction solvent and drying of the precipitate in vacuo,
1 H and 19 F NMR spectroscopy showed that the starting material was no longer present,
however, the peaks were very broad, hence there was difficulty in confirming if the desired
�-allyl complex had formed. A broad signal was seen at -168.1 ppm in the 19 F NMR
spectrum synonymous to that observed in the reaction described previously. However, the
reaction solvent that had been removed was analysed by 1 H NMR spectroscopy and found
not to contain starting material as in the previous reaction, rather, a new product 2-(buta-1,3-
dienyl)isoindoline-1,3-dione (133) [38] could be readily identified. Figure 3.6 highlights the
most reasonable route to this species, formed by the fluoride acting as a base to yield the