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

2.2.3 Synthesis of Allylic Chlorides
64
Chapter Two
Once all the allylic alcohols had been prepared they could be converted to their
corresponding chlorides with tetramethyl-�-chloroenamine using the method outlined by
Munyemana. [12]
2.2.3.1 Synthesis of ((2-chlorobut-3-enyloxy)methyl)benzene (106)
Scheme 2.24 Synthesis of (106)
The novel allyl chloride (106) was synthesised, by reaction of 1-(benzyloxy)but-3-en-2-ol in
DCM at 0 ºC, with one equivalent of tetramethyl-�-chloroenamine. The reaction mixture
was stirred at room temperature for 3 hours. After which, purification by chromatography
[DCM: cyclohexane (50:50)] afforded the product as an oil in 52 % yield. In addition, ((4-
chlorobut-2-enyloxy)methyl)benzene (107) was also isolated in a 15 % yield from the
purification column. Previously, (107) had been synthesised by Bandini and co workers [58]
via the reaction of allyl chloride with (allyloxymethyl)benzene, catalysed by Hoveyda’s
catalyst. Both products were fully characterised. However, since (107) is an unwanted co-
product no attempts were made when chlorinating the other allylic alcohols to isolate and
characterise it. It was reported by Munyemana that the chlorination of secondary alcohols
would give some rearranged chloride product, and that this was dependent on time, as the
rearranged chloride was thought to form after the formation of the desired chloride. [12]
Therefore, as all the allylic alcohols being converted to chlorides were secondary it was
likely that this might impair product conversions. The most probable mechanistic pathway
for the synthesis of the allyl chloride(s) is likely to involve the formation of an intermediate
iminium salt, and attack of the chloride displacing the amide which is a good leaving group,
affording the desired allylic chloride and N,N-dimethylisobutyramide as the co-product
(Scheme 2.25).