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

3.1 Introduction
3 Activation of Allylic Fluorides and Chlorides by Palladium
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Chapter Three
This chapter will focus on the activation of the C-Cl and C-F bond by reaction with Pd(0),
in order to examine whether identical reaction conditions can be employed and if the same
products can be generated.
3.1.1 Reactions of Allyl Chlorides with Palladium
In 1964 Dent, Long and Wilkinson synthesised �-allylic palladium chloride complexes
(yields > 80 %) by passing carbon monoxide through a mixture of the allylic chloride and
sodium chloropalladate dissolved in methanol. [1] Prior to this method �-allylic palladium
chloride complexes had been synthesised by reacting palladium chloride with an allylic
alcohol [2, 3] or chloride, [4, 5] however, the yields rarely exceeded 50 %.
Following on from this work, Ito and co-workers found that with Pd2(dba)3 oxidative
addition reactions occurred with allylic chlorides and that the substituents on the allylic
chloride affected the rate of reaction, with allyl chloride being more reactive than methallyl
chloride, crotyl chloride and cinnamyl chloride (Figure 3.1). [6]
Figure 3.1 Order of reactivity of allylic chlorides with Pd2(dba)3
The reaction was conducted by mixing an excess of the allylic chloride in a benzene
solution of Pd2(dba)3 at room temperature under nitrogen. The reaction mixture changes
colour from purple to a yellow-green. Washing with hexane removed the dba and
recrystallisation from methanol afforded the product as a yellow solid.
Scheme 3.1 Reaction of methallyl chloride with Pd2(dba)3
The majority of reported oxidative addition reactions of allylic compounds proceed via anti
addition, [7-11] with very few examples of syn addition. [12-16] In 1990 Kurosawa reported the
first syn oxidative addition of allylic chlorides to palladium, [17] followed very closely by
Vitagliano. [18]