Chemistry Reference
In-Depth Information
TABLE 8D.2. Intramolecular Carbonyl-Ene Reaction of Chiral Cr Complex
t
Bu
Cl
H
2
O
NO
O
Br
Cr
+
Cr
+
Br
O
O
N
OH
2
Cl
R
1
R
1
t
Bu
CH
3
R
1
R
1
23c
OH
X
H
R
3
R
2
X
MS 4A
R
2
O
R
3
Toluene, 4°C
%
Yield
%
ee
Substrate
Product
mol %
dr
0.8
77
93
R
1
= CH
3
, X = O
R
1
= CH
3
, X = NTs
R
1
= , X = O
R
1
R
1
>
30:1
R
1
R
1
CH
3
2.0
98
98
OH
>
30:1
H
X
H
3
C
X
1.0
96
96
>
30:1
O
H
3
C
2.5
88
—
94
R
1
R
1
R
1
R
1
R
1
= OCH
3
, X = CH
2
R
1
= , X = O
H
5.0
72
—
93
OH
X
X
O
CH
3
5.0
78
> 30:1
75
CH
3
H
3
CCH
3
OH
H
3
CCH
3
H
O
H
3
C
O
O
CH
3
CH
3
H
3
C
CH
3
CH
3
H
3
CCH
3
OH
1.0
94
20:1
96
H
3
CCH
3
H
O
H
3
C
O
O
CH
3
H
3
C
temperature, and bidentate diphosphines are effective as chiral ligands. In fact, the
substrates and chiral ligands structure are important factors for increasing enantioselec-
tivity. The use of DUPHOS ligand leads to high levels of enantioselectivity in aromatic
substrates (R = Ph) with an oxygen tether. In sharp contrast, BICP ligand facilitates the
reaction in the aliphatic substrates (R = C
4
H
9
), while DUPHOS complex is completely
inactive.
A number of chiral phosphine ligands and catalytic precursor have been screened,
and reaction conditions have also been optimized to more effi cient catalytic system for
Rh - catalyzed ene - type cyclization (Scheme 8D.44 ) [74] . When BINAP (12 mol %) as the
chiral ligand is used in the presence of [Rh(cod)Cl]
2
(5 mol %) and AgSbF
6
(20 mol %),
