Chemistry Reference
In-Depth Information
R
1
R
2
O
2
N
O
NO
2
O
94
+
R
4
R
3
R
1
R
2
R
3
R
4
r.t.
Up to 92% ee
R
1
=H,alkyl
R
2
=H,Me,CO
2
Et
R
3
= Ph, p-OH-Ph, p-NO
2
-Ph, 2-furyl
R
4
=Me,Et
Scheme 8A.51.
O
O
n
=0,1
n
Up to 84% yield
Up to 96% ee
R
2
R
1
NO
2
n
R
1
n
=0,1
59
(15% mmol)
O
2
N
R
2
CH
2
Cl
2
,rt
R
1
O
N
R
2
O
2
N
R
1
=H,Me
R
2
=H,Me,Et
Up to 88% yield
Up to 89% ee
O
R
3
C
H
3
R
3
CH
3
H
R
3
= Ph, CO
2
Me
Scheme 8A.52.
Dipeptides and tetrapeptides were reported as organocatalysts in the conjugate addi-
tion of nitroalkanes to cyclic enones by Tsogoeva et al. [110,111]. Catalyst
96
, a proline-
based dipeptide, was introduced to catalyze the conjugate addition with up to 88% ee
and up to 100% yield in the presence of
trans
- 2,5 - dimethylpiperazine as a cocatalyst
(Scheme 8A.53 ).
O
O
NO
2
Peptide catalyst
96
(2 mol %)
Trans
-2,5-dimethylpiperazine
CHCl
3
,5d,rt
Up to 100% yield
Up to 88% ee
+
R
2
R
1
NO
2
R
1
R
2
n
n
=1,2
n
n
=1,2
Scheme 8A.53.
Cinchona
alkaloid-derived bases such as
98
[113] ,
99
[114] , and
100
[115] were
employed as catalysts for the conjugate addition of nitroalkanes to α , β - electro - defi cient
olefi ns in good yields and with good enantioselectivities (Fig. 8A.6).
