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

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Chapter Two
sulphate and removal of solvent in vacuo yielded the crude product. Purification by
chromatography [chloroform: hexane (80:20)] afforded the product as an oil in 31 % yield,
which although lower than that reported in the literature (57 %) could be attributed to
difficulties in maintaining the reaction temperature at - 35 ºC for the whole reaction period.
4-methyl-2-hydroxybut-3-enyl benzoate (105) was formed, having previously been
synthesised by Ziegler, using slightly different conditions to those described earlier for the
synthesis of (100); a solution of (±)3-butene-1,2-diol (1.1 equivalents) and pyridine were
cooled to - 15 ºC, 4-methylbenzoyl chloride (80) (1 equivalent) was added and the mixture
left to stir at - 15 ºC for 15 hours, after which workup, drying over sodium sulphate and
removal of solvent in vacuo yielded the crude product. Purification by chromatography
[chloroform: hexane (80:20)] afforded the product as a white solid in 40 % yield. The solid
readily formed crystals which were analysed by single crystal X-ray crystallography (Figure
2.3). The synthesis of 2-hydroxybut-3-enyl 4-(trifluoromethyl)benzoate (104) was
conducted similarly but by cooling to -35 ºC for 17 hours. The crude product was purified
utilising the same solvent system, affording the product as a white crystalline product in 66
% yield (Figure 2.3).
Single crystals of (101), (104) and (105) suitable for single crystal structure analysis were
grown by dissolving the materials in a small amount of DCM and layering with hexane.
Molecular structures are shown in Figure 2.3 and Figure 2.4, with selected bond lengths (Å)
and bond angles (º) listed in Table 2.15 and Table 2.16.
Figure 2.3 Crystal structures of 2-hydroxybut-3-enyl 4-methylbenzoate (105) and 2-hydroxy
but-3-enyl 4-(trifluoromethyl)benzoate (104)