Chemistry Reference
In-Depth Information
Ar
Ar
H
OSiMe
3
149
CHO
10 mol %
149
PhCO
2
H
CHO
CHO
R
S
R
+
X
Toluene, rt
4ÅMS
X
R = Ph, 2 or 4-MeOC
6
H
4
,4-FC
6
H
4
,
4-NO
2
C
6
H
4
,Me,Et,n-C
3
H
7
,n-C
5
H
11
X = H,5-Cl, 5-MeO,5-Me, 3,4-(CH)
4
, 4,6-(MeO)
2
SH
Scheme 8A.90.
OMe
N
MeO
N
OMe
N
N
151
150
O
O
20 mol %
150
or
151
Cl
H
O
O
Ph
Na
2
CO
3
, MeCN, 80°C,
additive
H
Ph
64-95% ee
Scheme 8A.91.
8A.5. CATALYTIC ASYMMETRIC CONJUGATE ADDITION OF
HETEROATOM NUCLEOPHILES
8A.5.1. Conjugate Addition of Oxygen Nucleophiles
Merschaert et al. [172] reported an intramolecular conjugate addition of phenolic
nucleophiles to α , β-unsaturated esters for the asymmetric synthesis of 2-substituted
chiral chromanes. This reaction was recognized as the fi rst example of asymmetric
catalysis of an exo-trig [173] cyclization with an oxygen nucleophile. In the presence of
Cinchona
alkaloids or their derivatives as catalysts, this reaction was carried out in
toluene at 110°C under N
2
for 48 h and afforded the product in 90% conversion and in
82:18 R/S ratio (Scheme 8A.92).
Melchiorre et al. reported the fi rst catalytic and highly enantioselective β - hydroxylation
of
O
- centered nucleophiles to α , β-unsaturated ketones. In the presence of primary
amine salt
152
as catalyst, this reaction afforded optically active products with up to 94%
ee (Scheme 8A.93 ) [174] .
