Chemistry Reference
In-Depth Information
OCO
2
Me
OCO
2
Me
OCO
2
Me
OCO
2
Me
Ar
Ar
Figure 8B.27.
Unreactive allylic substrates.
[Mo]
−
R
R
R
X
X
−
A
B
Mo
Mo
N
u
N
u
R
R
R
Nu
l
Nu
b
Nu
Scheme 8B.55.
Allylic alkylations using highly unsaturated allylic substrates.
1.
OLi
Ph
N
OMe
Ph
CO
2
Me
CO
2
Me
+
Ph
Ph
OPO(OEt)
2
Ph
(C
7
H
8
)M o(CO)
3
,
L43a
, THF, 0°C
2. 1 N HCl
3. Boc
2
O, NEt
3
NHBoc
NHBoc
2:
1
95% ds, 98% ee (quant.)
Scheme 8B.56.
Allylic alkylations of imino glycinates.
Interestingly, only two of these products, namely the linear one and one of the
branched ones (
b
), were observed, and in analogy to normal allylic substrates, the
branched isomer was the major product (Table 8B.37). The lack of participation of
the additional double bond is surprising. The results obtained suggest that no
π
-
σ
-
π
isomerization of the
π
- allyl complex
A
formed in the ionization step to the isomeric
complex
B
occurs.
8B.4.1.4.2. Variation of the Nucleophile
Although malonates are used as standard
substrates in allylic alkylations, the malonate functionality is not one of the most useful
substituents, even if it can be converted into other functional groups. Several other
stabilized carbon nucleophiles have been investigated during the last years to enlarge
the synthetic potential of the Mo-catalyzed allylations.
For the synthesis of
- unsaturated amino acids, Trost and Dogra reacted imino
glycinate with cinnamylphosphonate [235]. In the presence of
L43a
, the required amino
acids were obtained in quantitative yield with excellent selectivities, although with mod-
erate regioselectivity (Scheme 8B.56 ).
γ
,
δ
