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

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Chapter Two
Two allyl alcohols were also synthesised with methyl substituents alpha to the benzoate
(Table 2.11). Methylallyl benzoate (87) was synthesised following the method outlined by
Nakamura et al. [55] 1 equivalent of 3-buten-2-ol was stirred in pyridine, the mixture cooled
to 0 °C and 1 equivalent of benzoyl chloride added. The reaction mixture was then stirred at
room temperature for 2 hours, after which aqueous workup, drying over magnesium
sulphate and removal of solvent in vacuo yielded the product as a colourless oil in 71 %
yield. Dimethylallyl benzoate (86) was synthesised following Yasui’s protocol [50] whereby
a flask was charged with 1.2 equivalents of sodium hydride, cooled to 0 ºC and 1 equivalent
of dimethylallyl alcohol added. The mixture was stirred at 0 ºC for 10 minutes and then at
room temperature for 15 minutes, after which the flask was cooled to 0 ºC, 1.2 equivalents
of benzoyl chloride added and the resultant mixture stirred at 0 ºC for 2 hours followed by
room temperature overnight. After work up, drying over magnesium sulphate, removal of
solvent in vacuo and distillation under reduced pressure dimethylallyl benzoate (86) was
formed as a colourless oil in a low 27 % isolated yield, attributable to losses incurred on the
Kugelröhr apparatus.
R Conditions Product Yield (%)
CH3
H
NaH, DMF,
2 h at 0 ºC,
Overnight stir at r.t
Pyridine, 0 ºC,
2 h at r.t
Table 2.11 Yields obtained of (86) and (87)
Once methylallyl benzoate (87) and dimethylallyl benzoate (86) were synthesised they were
reacted with 3 equivalents of allyltrimethylsilane and 5 mol % 2 nd generation Grubbs
catalyst in DCM, as previously described. However, with methylallyl benzoate (87) it was
found that after 48 hours the reaction had not gone to completion, but instead only 50 %
conversion had occurred, therefore an additional portion of Grubbs catalyst was added to the
reaction mixture and the reaction refluxed for a further 48 hours, an aliquot was taken from
the reaction mixture and conversion had increased to 75 %. The reaction mixture was
(86)
(87)
27
71