Chemistry Reference
In-Depth Information
(
R
,
R
)-di-
-Ti(salen)
8
(20% ee, 2 mol %)
μ
O
Urea hydrogen
peroxide adduct
(UHP)
+
S
S
Ph
Me
Ph
Me
MeOH, 0
°
C
ca. 80% ee
N
Cl
N
Ti
O
Cl
O O
Ph Ph
(salen)
Ti
Ti(salen)
O
8
(
R
)-Ti(salen)
MeOH
(
R
,
R
)-di-
μ
-Ti(salen)
(
R
)-Ti(salen)
(
S
,
R
)-di-
μ
-Ti(salen)
Stable and less soluble
MeOH
(
S
,
S
)-di-
μ
-Ti(salen)
(
S
)-Ti(salen)
Scheme 12.11.
La(O
i
-Pr)
3
-(
R
)-BINOL
(40% ee, 10 mol %)
O
O
O
Ph
3
As=O (10 mol %)
+
TBHP
Me
Ar
Me
Ar
MS 4A, THF, rt
ca. 70% ee
Ar=
MOMO
O
O
Scheme 12.12.
complex La[(
R
) - binaphthoxide][(
S
) - binaphthoxide](Ph
3
As = O)
2
is the reason for asym-
metric amplifi cation after precise mechanistic investigation (Scheme 12.12) [21].
12.2.4. Asymmetric Aldol and Allylation Reactions
Mikami and others reported an ene and Diels-Alder reactions using Ti(IV)-BINOL
system [22]. The preparation of chiral catalysts with moderate ee was found to be very
important for the induction of asymmetric amplifi cation. Also, in the case of vinylogous
aldol reaction of Chan's diene, the mode of preparation made a large difference on the
NLE. When the chiral catalyst was prepared from Ti(O-
i
- Pr)
4
and (
R
) - BINOL with
