Chemistry Reference
In-Depth Information
becomes insufficient for recyclization and thus should be supplemented. One of the advan-
tages of this catalytic system is that (
S
,
S
)-BDPP can be recovered in high yield (up to 87%)
from the reaction mixture after the completion of the run and the recovered (
S
,
S
)-BDPP
can be used in further reactions.
9.4.2.4
Co
2
Rh
2
-catalyzed PK-type reaction using olefinic aldehydes as an alkene
and CO source
44
From previous studies,
42, 43
-unsaturated aldehyde as the source of alkene
and CO could be envisioned. However, the use of an
the use of
α
,
β
-unsaturated aldehyde as the
source of alkene and CO in the PKR was first realized by Chung's group.
44
They studied a
reaction of an alkyne with
α
,
β
-unsaturated aldehydes such as acrolein, crotonaldehyde, and
cinnamylaldehyde in the presence of
Co
2
Rh
2
(Scheme 9.15). A PK-type reaction product
was obtained in reasonable to high yields (Scheme 9.16). It is somewhat surprising that
α
,
β
-
unsaturated aldehydes, known as poor substrates for the PKR, can be used as a source of
CO and alkene. The reaction was highly regioselective with respect to alkenes and alkynes.
Treatment of the unsymmetric internal alkyne afforded one isomer as the sole product.
α
,
β
O
O
Co
2
Rh
2
Ph
+
Ph
R
H
130
°
C, 18 h, THF
R
Yield (%)
R
H
Me
Ph
60
77
75
Scheme 9.15
O
O
Co
2
Rh
2
R
2
+
R
1
R
2
Me
H
130
°
C, 18 h, THF
Me
R
1
Yield (%)
R
1
R
2
H
H
Ph
Ph
Bu
Ph
77
70
71
Scheme 9.16
According to the reusability test of the catalytic system for the reaction between cinnamic
aldehyde and phenylacetylene, the catalytic activity of
Co
2
Rh
2
nanoparticles was retained
for at least five runs.
