[86]. However, the reactions were rather slow and the enantioselectivity did not
surpass 46% (Scheme 45).
4.2 Catalysis via Metal-Ligand Cooperation
Thus far, in all hetero-Michael addition reactions, the catalyst has functioned as a
Lewis acid activating the α,β-unsaturated nitrile for 1,4-addition and stabilising the
developing negative charge on the nitrogen atom. An entirely different mode of
Scheme 44 Ni PCP pincer complexes as catalysts for the aza-Michael addition
Table 15 Oxa-Michael addition of alcohols to acrylonitrile by 44
a
Entry
ROH
X:nitrile:ROH
Time (h)
Yield (%)
TON
1
m-Cresol
1:2000:4000
36
99
~2000
2
MeOH
1:200:2000
1.0
100
200
3
EtOH
1:200:2000
1.0
87
174
4
C F 3 CH 2 OH
1:200:2000
0.5
90
180
5
n-PrOH
1:200:2000
8
64
128
6
i
PrOH
1:200:2000
24
23
46
7
BnOH
1:200:2000
1.0
100
200
a Reaction yields were determined by 1H NMR spectroscopy or GC/MS
362
B. Guo et al.