Chemistry Reference
In-Depth Information
TABLE 8D.3. Intermolecular D-A Reaction of B Cat 38
B Cat
(mol %)
Diene
Product
° C (h)
% Yield
exo
:
endo
% ee
38a
(6)
−
95 (1)
99
91:9
91
CHO
38b
(6)
−
95 (1)
97
91:9
96
Me
38a
(6)
− 95 (1)
99
91:9
92
CHO
38b
(6)
− 95 (1)
99
91:9
96
Br
38b
(6)
− 78 (13)
96
96
97
Me
CHO
38a
(6)
− 95 (1)
98
98
97
B
r
CHO
38b
(6)
− 95 (1)
98
98
97
38b
(20)
− 78 (24)
85
85
94
Me
CHO
38a
(6)
−
95 (2)
95
95
96
B
r
CHO
38b
(6)
−
95 (2)
97
97
96
38a
(20)
−
78 (24)
91
5:95
92
38b
(20)
−
78 (24)
58
6:94
92
Me
CHO
38a
(6)
−
95 (2)
81
6:94
92
38b
(6)
−
95 (2)
85
7:93
92
Br
CHO
in CH
2
Br
2
and oxazaborolidine (ratio of 0.8:1.0). In most cases, the catalyst (
41
) using
only 4 mol % leads to excellent yield and enantioselectivity and is more effective than
catalysts
38 - 40
that generally require the high catalyst loading (10
20 mol %). The use
of furans as dienes produces chiral cyclohexane derivatives in which the six carbons are
all functionalized in high yield and enantioselectivity.
The asymmetric HDA reaction with Danishefsky's diene catalyzed by Ti catalysts
generated from a library of 13 chiral ligands or activators (
L
1
- L
13
) has been reported by
Ding et al. (Scheme 8D.68) [104]. A catalyst library contains 104 members. The Ti cata-
lysts with
L
4
,
L
5
,
L
6
, and
L
7
give 63-100% yield and 76.7-95.7% ee. On the other hand,
ligands with sterically demanding substituents at the 3,3
∼
- positions (
L
8
- L
13
) are found to
be detrimental to the reaction. It is clarifi ed that both
L
5
/Ti/
L
5
and
L
5
/Ti/
L
6
as optimized
catalysts are the most effi cient for the reaction of a variety of aldehydes, including aro-
matic, aliphatic, and olefi nic derivatives.
′
