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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
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