Chemistry Reference
In-Depth Information
[2
1] cycloaddition reactions might be larger than that in the homogeneous reactions.
Thus, the reaction was highly dependent upon the substituent(s) on the allene moiety.
The reaction was extended to the catalytic formation of bicyclo[5.3.0]dec-1,7-dien-
9-ones in acceptable yields (Scheme 9.18). Complete chemoselectivity was observed
in the formal [2
+
2
+
1]-cycloaddition, leading to the exclusive construction of the
bicyclo[5.3.0]dec-1,7-dien-9-one framework in acceptable yields compared to those in
previous works using a homogeneous catalyst.
42
+
2
+
R
R
TsN
Cat.
TsN
O
110
C, 6 h, toluene
°
•
Yield (%)
R
H
Me
Ph
64
73
72
Scheme 9.18
9.4.2.6
Co
2
Rh
2
-catalyzed PK-type reaction of allenes
51
Recently, the chemistry of allenes has attracted a lot of attention, presumably due to
their high reactivity. However, although many transition metal-catalyzed cycloaddition of
allenes have been disclosed,
49, 50
there was no report on the use of allenes as substrates
in the intermolecular PK-type reaction until 2008. The first use of allenes in inter- and
intramolecular PK-type reactions was reported by Chung
51
using
Co
2
Rh
2
as a catalyst.
They studied the catalytic formation of cyclopentenones via a [2
+
2
+
1] cycloaddition of
two allenes and carbon monoxide.
O
O
Cat. (5 mol%)
•
2
+
Ph
Ph
CO, 130
°
C, toluene
Ph
Ph
Ph
A
B
Cat.
CO (atm)
Time (h)
Yield(A / B) (%)
1
2
2
2
2
18
18
12
6
6
Co
2
Rh
2
Co
2
Rh
2
Co
2
Rh
2
Co
2
Rh
2
[Rh(CO)
2
Cl]
2
45/8
59/3
62/10
68/12
32/25
Scheme 9.19
Using phenylallene as a substrate, they screened the reaction conditions including
the reaction temperature, the reaction time and the CO pressure (Scheme 9.19). Two
carbonylated cyclic enones were isolated in various ratios and yields depending upon
