Chemistry Reference
In-Depth Information
HO
OH
HO
R
1
O
HO
OH
O
OH
40
R
1
O
R
2
O
HO
CO
2
Me
42
43
HO
CO
2
Me
41
R
1
O
R
2
R
1
O
R
2
R
1
O
Co
2
(CO)
8
+
R
1
O
R
1
O
O
O
R
1
O
R
2
H
H
43
44
45
R
1
=H,TBS
R
2
=TMS,
n
-Bu, Ph, H
Scheme
4.11
Highly diastereoselective
construction
of
optically
active bicyclo-
[3.3.0]octenone derivatives.
PKRs of enynes
43
were executed using both conventional thermal conditions and an al-
ternative procedure involving a mild oxidant (TMANO). As a result, bicyclo[3.3.0]octenone
derivatives
44
and
45
were obtained in high yields with good to excellent diastereoselectiv-
ity when the substrates contained bulkier R
2
substituents. In contrast, when the R
2
group
was hydrogen, the diastereoselectivity dropped to a nearly 1:1 ratio
In 1996, Alcaide and Sierra
et al.
successfully applied the PKR for the synthesis of
fused tricyclic
-lactams.
13
In this study, various enyne-2-azetidinones
46
, which were
prepared using standard methodology, were used as substrates for the cyclization. The
treatment of enyne-
-lactams
46a-c
with CO
2
(CO)
8
followed by
in situ
thermal or TMANO
decomposition of the resultant alkyne-CO
2
(CO)
6
complexes gave tricyclic
-lactams
47a-c
as single stereoisomers in good to excellent yields (Scheme 4.12).
O
H
(i) Co
2
(CO)
8
/
Toluene, RT
(ii)
BnO
BnO
H
N
N
Δ
O
O
(+)-46a
(+)-47a
(95 %)
O
H
(i) Co
2
(CO)
8
/CH
2
Cl
2
(ii) TMANO 0 °C to RT
N
O
PMP
N
O
PMP
47b
(80 %)
46b
(i) Co
2
(CO)
8
/CH
2
Cl
2
(ii) TMANO 0 °C to RT
O
N
N
O
O
H
47c
(65 %)
46c
Scheme 4.12
Synthesis of fused tricyclic
β
-lactams.
