Chemistry Reference
In-Depth Information
TABLE 8B.49. Asymmetric Rh - Catalyzed Allylations Using Cinnamyl Derivatives as Substrates
OAc
Ar
MeO
2
C
CO
2
Me
MeO
2
C
CO
2
Me
b
CH
2
(CO
2
Me)
2
Rh complex/
or
+
L
,
OAc
Ar
Ar
react. cond.
b
l
Ar
l
Product
Yield
b
(%)
React.
Cond.
a
Entry
Substrate
Ar
L
b
:
l
ee (%)
Reference
1
l
P h
L54
A
95
49:51
14
280
2
l
P h
L55
A
95
2:98
—
280
3
b
P h
L55
B
94
98:2
97
281
4
b
4 - MeC
6
H
4
L55
B
97
88:12
94
281
5
b
4 - CF
3
C
6
H
4
L55
B
97
99:1
97
281
6
b
4 - ClC
6
H
4
L55
B
93
97:3
95
281
7
b
1 - Naphthyl
L55
B
94
60:40
95
281
a
Reaction conditions:
A
: NaCH(CO
2
Me)
2
, [Rh(COD)Cl]
2
, THF, 68 ° C;
B
: CH
2
(COOMe)
2
, Cs
2
CO
3
, Rh(dpm)
(C
2
H
4
), toluene, 40°C, high dilution, slow addition of the nucleophile.
b
Overall yield.
OAc
MeO
2
C
CO
2
Me
MeO
2
C
CO
2
Me
NaCH(CO
2
Me)
2
[Rh(COD)Cl]
2
/
L55
,
THF, 68°C
+
Ph
R
Ph
R
Ph
R
p
d
R
p
/
d
p
(% ee)
d
(% ee)
Yield (%)
p = proximal
d = distal
Me
Et
75
70
10:90
14:86
80
82
13
26
Scheme 8B.70.
Asymmetric Rh-catalyzed alkylations of secondary allylic substrates.
excellent Michael acceptors and were used for the stereoselective synthesis of a range
of natural products such as the lycoranes.
Lautens et al. investigated the desymmetrization of
meso
- substrates under catalysis
with chiral Rh complexes, and they reported on the fi rst rhodium - catalyzed asymmetric
addition of boronic acids to oxabicyclic alkenes [283]. The reaction proceeds under very
mild conditions and generates compounds with multiple stereogenic centers in high yield
and excellent diastereo- and enantioselectivity (Table 8B.51). Best results were obtained
if the reactions were run in THF with aq. Cs
2
CO
3
as base and [Rh(COD)Cl]
2
combined
with ligand (
R
,
pS
) -
L40b
(Fig. 8B.32 ).
o
-Substituents at the aryl boronic acid are not
accepted, but all other substituted boronic acids gave ees > 94% (entries 1 - 4). Interest-
ingly, alkenylboronic acids can be used as well (entry 5).
