Chemistry Reference
In-Depth Information
R
R
R
Ph
O
O
N
Ph
N
Pd
Pd
R
P
P
Ph
Ph
nx
(
endo,cis
)
xc
(
exo,cis
)
Reactive isomer
R
R
Ph
Ph
N
O
N
O
R
Pd
Pd
Ph
P
P
Ph
R
xt
(
ex o,t r ans
)
nt
(
endo,tr ans
)
Major isomer
Scheme 8B.27.
Possible intermediates of the allylic alkylation described in Scheme 8B.26.
with an alkoxy or OH moiety generated by reaction with the Pd
0
species (cf. Scheme
8B.28). This preference is enhanced by spatial constraints if
DPPBA
ligands are
employed [38,123]. In contrast, the reaction of butadiene monoepoxide with a dialkyl
malonate under standard salt-free conditions (cf. Section 2B.2.1.4.2) mainly yields the
linear product.
H
Nu
O
O
O
Nu H
OH
R
R
[Pd]
Nu
R
R
[Pd]
[Pd]
Is o mer s v ia
π
π
rearrangement
-
σ
-
Scheme 8B.28.
Pd-catalyzed allylic substitution with vinylepoxides as substrates.
However, the reaction of isoprene monoepoxide with β - keto esters preferentially
gave the branched alkylation products in the form of hemiacetals (Scheme 8B.29).
Success with these reactions required careful optimization of reaction conditions in
dependence of the β-keto ester. In the case of ethyl acetoacetate (R = CH3), addition
of a fl uoride source was essential for gaining a useful level of regioselectivity. The extent
