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

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Chapter Four
nucleophilic substitution of (137), occurred at the more sterically hindered carbon, affording
(139) as the major product [(138):(139), (23:77)] (Scheme 4.1). This is known as the
memory effect and has also been observed by Acemoglu and Williams in the reactions of
allylic acetates with NaCH(CO2t-Bu)2, using bulky aliphatic phosphine ligands. [11]
Scheme 4.1 Synthesis of (138) and (139)
Often nucleophilic attack can also be directed by nearby atoms, as demonstrated in Scheme
4.2 where formation of the 1,4 adduct is preferred due to the electronic effect of the epoxide
oxygen. Palladium catalyses the ring opening of the epoxide leading to formation of the �-
allyl palladium complex with generation of an alkoxide anion. This can then abstract a
proton from the nucleophile, affording �-hydroxy-�-allylpalladium. Subsequent reductive
[12, 13]
elimination can afford either the 1,4 or 1,2 products.
Scheme 4.2 1,2-addition and 1,4-addition products from �-hydroxy-�-allyl palladium