Chemistry Reference
In-Depth Information
KH, THF;
OR*
KH, THF, Cl
2
C=CHCl;
HO
O
R*OH
OR*
n
-BuLi; (CH
2
O)
n
Br
4a
4b
5a
(74%)
5b
(86%)
6a
(86%)
6b
(96%)
Me
Me
Me
Me
Me
OH
O
O
OH
Me
Me
Me
Me
Me
Me
Me
4a
4b
Scheme 5.12
7.3:1 mixture of diastereomers in a 65% yield. Remarkably, with
6b
the bicyclization
could be performed at room temperature under nitrogen to give
7b
in a 54% yield and
with a diastereomeric ratio of 15.7:1. Moreover, in both cases the diastereomers could be
readily separated by simple column chromatography. For
7b
, a single crystal of the minor
diastereomer was used to establish the absolute configuration at C5 by X-ray diffraction
analysis, and this was found to be (
S
). Accordingly, that at C5 of the major diastereomer of
7b
was found to be (
R
).
Tab l e 5 . 2
O*R
O*R
OR*
Co
2
(CO)
8
+
O
O
O
O
O
H
H
6a
,
6b
(Major for
7a
)
(Major for
7b
)
Product
Yield (%)
Dr
R*O-
Conditions
Me
Me
Isooctane, 50
°
C,
17 h
65
7.3:1
O
O
7a
Me
Me
Me
Me
Me
Me
Me
Me
Me
O
O
Hexane, rt,
4 h
54
15.7:1
7b
Me
