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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
 
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