Chemistry Reference
In-Depth Information
Gautun and others reported the hetero-Diels-Alder reaction of
N
- sulfi nyl dienophile
using metal trifl ate - bis(oxazoline) catalyst. Zn(OTf)
2
showed obvious positive NLE; on
the contrary, Cu(OTf)
2
did a nearly linear relationship between the ee of ligand and the
bicyclic product (Scheme 12.21 ) [32] .
Me
Me
O
O
+
M(OTf)
2
N
N
Ph
Ph
(Low ee, 10 mol %)
O
S
N
S
+
N
TMSOTf (100 mol %)
O
Cbz
Cbz
endo
CH
2
Cl
2
, -75
°
C
M=Zn: positive NLE
Cu: weak NLE
Scheme 12.21.
12.2.6. Asymmetric Ring Opening of
meso
- Epoxide
Nozaki and others reported an asymmetric alternating copolymerization of cyclohexene
oxide and carbon dioxide. The catalyst was prepared from diphenyl prolinol
15
of 40%
ee and diethylzinc, and the ee of diol was determined to be ca. 50% ee after the hydro-
lysis of the obtained polymer (Scheme 12.22) [33]. This is the fi rst example of nonlinear
phenomenon in the asymmetric synthesis of chiral polymers with main-chain chirality.
Ph
Ph
OH
NH
15
(ca. 40% ee, 5 mol %)
Et
2
Zn (5 mol %)
EtOH
O
+
CO
2
Toluene, 40
°
C
O
O
O
n
ca. 50% ee
Scheme 12.22.
Mai and Schneider showed positive NLE in the enantioselective aminolysis of
cis
-
stilbene oxide. Sc(III)-chiral pyridine complex catalyzed the reaction (Scheme 12.23)
[34] .
