Chemistry Reference
In-Depth Information
The two - directional hetero - ene reaction sequence, fi rst with pyruvate and then with
glyoxylate, is attempted by using chiral SEGPHOS-Pd, and then BINOL-Ti catalysts,
sequentially (Scheme 8D.10). (
R
)/(
S
)-diol product bearing both quaternary and tertiary
carbon centers is obtained by using (
S
)-BINOL in 67% yield and
99% ee after desi-
lylation by TBAF (
dr
= 92/8). In contrast, the treatment with (
R
) - BINOL - Ti gives the
(
R
)/(
R
)-diol product in 61% yield and 97% ee (
dr
= 91/9).
>
TIPSO
Me OH
O
+
CO
2
Et
HCO
2
Et
92% ee (
R
)
1) (
R
)-BINOL/Ti(O
i
Pr)
4
1) (
S
)-BINOL/Ti(O
i
Pr)
4
(10 mol % each)
(10 mol % each)
2
)
T
B
2
T
B
O
O
OH
Me
O
H
O
H
Me
OH
EtO
2
C
CO
2
Et
EtO
2
C
CO
2
Et
(
R
)/(
R
)
97% ee (61%)
(
R
)/(
S
)
>99% ee (67%)
dr
= 92/8
dr
=91/9
Scheme 8D.10.
It is already reported that the asymmetric glyoxylate-ene reaction with silyl (TMS,
TBDMS) enol ether catalyzed by chiral BINOL-Ti
1
affords chiral diol bearing silyl enol
ether in high yield and enantioselectivity (Scheme 8D.11) [33]. In the BINOL-Ti cata-
lytic system, the use of ketone instead of aldehyde as an enophile led to lower yield and
enantioselectivity.
1)
(
R
)-BINOL-Ti
1
(10 mol %)
O
H
O
OH
O
Si
O
+
2
MeO
2
C
CO
2
Me
HCO
2
Me
2) HCl/MeOH
Si
= TBDMS
>99% ee (>99%
anti
)
TMS
H
+
Two-directional
O
H
O
Si
OH
O
Si
OH
ene reaction
MeO
2
C
CO
2
Me
CO
2
Me
Scheme 8D.11.
