Chemistry Reference
In-Depth Information
R
1
R
1
Pure Co
2
(CO)
8
(5-10 mol%)
DME, 60 °C, CO (1 atm)
R
2
Z
Z
O
( )
n
R
2
Z = C(CO
2
Et)
2
, R
1
= H, R
2
= H (n = 1): 83%
Z = C(CO
2
Et)
2
, R
1
= H, R
2
= H (n = 2): 77%
Z = C(CO
2
Et)
2
, R
1
= H, R
2
= Me (n = 1): 85%
Z = NTs, R
1
= H, R
2
= H (n = 1): 86%
Z = NTs, R
1
= Me, R
2
= H (n = 1): 78%
EtO
2
C
EtO
2
C
Pure Co
2
(CO)
8
(7.5 mol%)
EtO
2
C
O
DME, 60 °C, CO (1 atm)
EtO
2
C
H
OAc
OAc
78%
Scheme 3.19
Compared with Co
2
(CO)
8
,theCo
2
(CO)
6
-alkyne complex is generally more stable,
and can be purified even by silica-gel chromatography. Livinghouse used Co
2
(CO)
6
-2-
methylbut-3-yn-2-ol as a pre-catalyst (Scheme 3.20). The complex was treated with tri-
ethylsilane and cyclohexylamine for the dissociation of the alkyne, and was submitted to
the reaction. The reaction proceeded smoothly under the ambient pressure of CO atmo-
sphere.
20
Also in this case, a stereospecific reaction of an enyne with
Z
-olefinic moiety was
listed.
Co
2
(CO)
6
OH
(5-10 mol%)
Et
3
SiH (5 mol%)
CyNH
2
(15 mol%)
R
1
R
1
R
2
Z
Z
O
DME, 65 °C, CO (1 atm)
( )
n
( )
n
R
2
Z = C(CO
2
Et)
2
, R
1
= H, R
2
= H (n = 1): 92%
Z = C(CO
2
Me)
2
, R
1
= H, R
2
= H (n = 2): 86%
Z = C(CO
2
Et)
2
, R
1
= H, R
2
= Me (n = 1): 95%
Z = NTs, R
1
= H, R
2
= H (n = 1): 77%
Z = NTs, R
1
= Me, R
2
= H (n = 1): 92%
Scheme 3.20
Based on the same concept, Krafft used the Co
2
(CO)
6
-enyne complex. The transfer of
Co
2
(CO)
6
to other enynes as substrates readily occurred without the aid of silane, and could
operate as a catalyst (Scheme 3.21). In some cases, amine was not needed.
21