Chemistry Reference
In-Depth Information
[Rh(cod)Cl]
2
(5 mol %)
Me
H
BINAP (12 mol %)
Me
O
5
ste
ps
AgSbF
6
(20 mol %)
(CH
2
Cl)
2
, r.t.
HO
O
*
O
O
O
O
within 2-10 min
O
O
(
R
)-BINAP >99% ee (+) (99%)
(
S
)-BINAP >99% ee (-) (98%)
N
Me
N
O
O
(+)-Pilocarpine
Scheme 8D.47.
CO
2
Me
[Rh(diphosphine)]
2
(SbF
6
)
2
(5 mol %)
CH
2
Cl
2
, r.t.
O
CO
2
Me
CO
2
Me
*
*
+
O
O
(
S
)-BINAP
28% ee (
S
) (90%)
93% ee (
R
) (59%)
18% ee (
S
) (10%)
>95% ee (
R
) (6%)
(
S
,
S
)-skewphos
Ph
2
P
PPh
2
CO
2
Me
[Rh{(
S
,
S
)-skewphos}]
2
(SbF
6
)
2
CO
2
Me
(5 mol %)
CH
2
Cl
2
, 0
∞
C, 96 h
Ts
Ts
90% ee (62%)
Scheme 8D.48.
proceeds even with such a sterically demanding trisubstituted olefi nic ether, along with
the formation of isomerized
endo
-cyclic secondary product. The key to success in
increasing the enantioselectivity and olefi nic regioselectivity is the use of (
S
,
S
) - skewphos
((2
S
,4
S
) - 2,4 - bis(diphenylphosphino)pentane (
S
,
S
) - BDPP) rather than BINAP. The
reactions with (
S
,
S
)-skewphos proceed slowly, but olefi nic regioselectivity increases up
to 98%, maintaining high chemical yield and high enantioselectivity of the major
