Chemistry Reference
In-Depth Information
syn-Pentane
N
N
Me
Me
Ar
Ar
Mo
Mo
Me
H
O
O
O
Me
O
O
O
Ar
Ar
H
I
II
N
Me
O
Ar
Mo
OMe
O
O
O
Ar
Me
III
Figure 8E.3.
Proposed model for enantioselectivity in the enantioselective RCM of enol ethers.
resolution of planar stereogenic ferrocenes by Mo-catalyzed enantioselective RCM reac-
tions was reported [29]. Although the substrate scope in this study is limited, high levels
of enantioselectivity are achieved with commercially available Mo alkylidene
4a
. Alkene
substitution patterns are crucial for effective kinetic resolution; substrates bearing a
terminal and a 1,1-disubstituted olefi n (Eq. 8E.1) furnish the best selectivities. Two
additional points regarding this study merit mention: (1) Complex
4a
is the only chiral
complex examined; alternative chiral Mo complexes may deliver improved selectivity.
(2) In many cases, signifi cant homodimerization of the substrate occurred, rendering a
precise determination of the selectivity diffi cult [30] .
10 mol %
i-Pr
i-Pr
N
Me
Mo
O
Ph
Me
O
SiMe
3
Me
3
Si
SiMe
3
Me
3
Si
SiMe
3
Me
3
Si
Me
Me
Fe
Fe
Fe
+
Me
ent-
4a
Racemic
C
6
H
6
[5 mM], 50
°
C, 24 h
45% yield, 97% ee
52% yield, 81% ee
k
rel
> 50
(8E.1)
