Chemistry Reference
In-Depth Information
of solvent or with undistilled THF in air. A supported chiral ligand that effectively
promotes the asymmetric reaction can be recycled at least fi ve cycles.
Recently, Yamamoto and Kawasaki reported on Ag(I)-catalyzed asymmetric azo
HDA reactions (Scheme 8D.73) [112]. The reaction with 2-azopyridine and siloxydiene
catalyzed by the combination of AgOTf (10 mol %) and (
R
) - BINAP (5 mol %) proceeds
in EtCN as a solvent to afford the corresponding cycloadducts in high yield and enan-
tioselectivity. The cycloadduct (R
1
, R
2
= Me) can be converted into the protected
1,4 - diaminoalcohol by SmI
2
-mediated cleavage of the N-N bond with trifl uoroacetyl
group as a key step [113].
The practical asymmetric HDA reaction with less reactive methyl-substituted
Danishefsky-type dienes in the presence of [Rh
2
{(
S
) - BPTP}]
4
(
45
) was reported by
R
2
R
2
Troc
(
R
)-BINAP (5 mol %)
AgOTf (10 mol %)
N
Troc
N
N
N
+
N
EtCN
-78 to -40
TIPSO
TIPSO
Ar
°
C
R
1
R
1
R
1
= Me
R
2
= Me
>99% ee (87%)
95% ee (84%)
92% ee (74%)
Me
Bn
n
-C
5
H
11
Me
N
HTFA
Troc
CO
2
Me
SmI
2
N
N
N
N
TIPSO
Ar
TIPSO
COCF
3
TIPSO
NHCO
2
Me
71%
Scheme 8D.73.
R
1
= OMe
O
R
3
O
R
2
R
2
= H, R
3
=PhC C
92% ee (91%)
0.002 mol %: 91% ee (96%)
R
1
O
45
(1 mol %)
+
3
H
CH
2
Cl
2
Et
3
SiO
R
2
then TFA
M
e
O
O
R
1
= Me
R
3
N
O
H
R
2
O
N
Rh
O
Rh
R
2
= Me, R
3
=PhC C
97% ee (81%)
45
Scheme 8D.74.
