Chemistry Reference
In-Depth Information
Tab l e 5 . 9
O
Me
Me
R
75a-d
H
N
O
2
S
H
O
Me
Me
Co
2
(CO)
8,
rt;
O
+
R
O
N
O
2
S
Xc
76a,b
(R = Me, CH
2
OMe)
O
74a
(R = Ph)
74b
(R = SiMe
3
)
74c
(R = Me)
74d
(R = CH
2
OMe)
To l u e n e ,
45 °C,12 h (for
74a
,
b
)
or NMO, CH C
22,
0
°
C to rt, 1-18 h
(for
74c
,
d
)
R
Alkyne
R
Product
Yield (%)
Dr
74a
Ph
75a
93
> 800:1
SiMe
3
74b
75b
78
> 800:1
75c
55
318:1
74c
Me
24
1.7:1
76a
75d
52
> 800:1
74d
CH
2
OMe
23
1.1:1
76b
were not separable by chromatography. The reaction of
74a
with norbornene (NMO) took
place with somewhat lower yield (54%), but still with excellent diastereoselectivity (125:1
dr). The absolute configuration of adducts
75a
and
75b
were ascertained by a combination
of CD spectra, chemical correlation, and X-ray diffraction analysis.
As an illustration of the synthetic applications of these readily obtained stereopure PK
adducts, Scheme 5.55 depicts the preparation of the 4-substituted cyclopentenone (
R
)-
80
.
52
Chemoselective hydrogenation of the cyclopentenone double bond and reductive cleavage
of the trimethylsilyl group in
75b
were simultaneously achieved by treatment with zinc
dust in acetic acid, to give a mixture of epimers at C3 from which the major component