Chemistry Reference
In-Depth Information
H
H
OC
O
O
Co
O
H
O
Ph
CO
Co(CO)
3
O
H
H
H
H
Ph
Scheme 5.37
Seeking to enhance stereocontrol in this intermolecular process, and taking into account
the ability of amino or of alkylthio groups, tethered either to the alkene
38
or to the alkyne
39
partner, to act as a coordinating ligands in alkyne-dicobalt carbonyl complexes, Pericas,
Riera, and co-workers examined several chiral alcohols bearing an appropriately positioned
group able to interact with the metal center along the reaction pathway.
40
They found out
that 10-methylthioisoborneol
9a
, a previously known chiral alcohol easily prepared from
camphor,
41
appears to function within this conceptual design. The requisite alkoxyacetylene
dicobalt hexacarbonyl complex
52a
was obtained in a 62% overall yield from
9a
by
the reaction sequence depicted in Scheme 5.38, involving conversion into the 1-alkoxy-
1,2-dichloroethene derivative
51a
14
and one-pot transformation of this compound into
52a
through the trimethylsilylated alkoxy acetylene derivative.
42
The same procedure was
applied later on to the preparation of the related complexes
52b
and
52c
.
43
Me
Me
Me
Me
CHCl=CCl
2
, KH, THF
51a
(R = Me; 78%)
51b
(R = CH
2
CMe
3
; 74%)
51c
(R = Ph; 77%)
Cl
O
OH
H
R
R
S
S
Cl
9a
(R = Me)
9b
(R = CH
2
CMe
3
)
9c
(R = Ph)
n
-BuLi, Et
2
O, Me
3
SiCl
Me
Me
Me
Me
Co
2
(CO)
8,
hexane;
K
2
CO
3,
MeO
H
O
H
O
S
R
R
(OC)
3
Co
Co(CO)
3
S
SiMe
3
52a
(R = Me; 80%)
52b
(R = CH
2
CMe
3
; 72%)
52c
(R = Ph; 71%)
Scheme 5.38
