Chemistry Reference
In-Depth Information
Table 9.14
Bisthiourea catalysed Baylis-Hillman reaction
O
bisthiourea
(0.4 eq)
bisthiourea
OH
O
O
+
R
R
H
F
3
C
S
S
CF
3
base (0.4 eq)
without solvent
NH
HN
(2.0 eq)
NH
HN
F
3
C
CF
3
run
base
yield (%)
ee (%)
R
1
DMAP
Ph
88
53
2
imidazole
Ph
40
57
3
DMAP
4-CF
3
C
6
H
5
4-CF
3
C
6
H
5
C
6
H
13
99
33
4
imidazole
95
44
5
DMAP
63
60
c-C
6
H
11
6
DMAP
72
90
DMAP: 4-dimethylaminopyridine.
C
2
-symmetric bisthiourea carrying a guanidine function at the molecular centre has been
designed as an alternative catalyst and applied to asymmetric Henry reaction; adduct is
formed in high yield and high enantioselectivity [43] (Scheme 9.8). Wide generality in
substrate is observed. Addition of potassium iodide under heterogeneous conditions is
necessary to avoid retro-aldol reaction and self aggregation of the catalyst is suggested by a
positive nonlinear effect in yield and enantioselectivity.
9.4.3 Urea-Sulfinimide Hybrid Catalyst
Tan et al. [44] succeeded in developing a new urea-sulfinimide catalyst that promotes the
indium mediated allylation of acylhydrazones (Scheme 9.9). Incorporation of Lewis base
functionality in proximity to the urea moiety is designed to promote the addition of
organometallic reagents to the C
ΒΌ
N bond of acylhydrazones through dual activation.
O
Et
3
N
H
H
N
Ar
N
S
S
N
Ar
N
H
H
O
H
R
Figure 9.10
Supposed transition state for bisthiourea catalysed Baylis-Hillman reaction
