Chemistry Reference
In-Depth Information
pure 3-azabicyclo[3.3.0]octen-7-one derivatives via PKR was described by the same
group.
17
Also in 2002, Jiang
et al.
described a new strategy for the preparation of enantiopure,
fused cyclic chiral amino acids
65
.
18
Optically pure enyne amino acid derivatives
64
,
which were easily prepared by an alkenylboronic acid-mediated Mannich-type reaction,
were successfully used for intramolecular PK reactions with a variety of catalytic systems.
Optimal results featuring yields up to 82% were obtained using 10 mol% Co
2
(CO)
8
and
1,6-enyne amino esters
64
in the presence of 60 mol% Bu
3
PS co-ligand in benzene at 70
◦
C
under 1 atm of carbon monoxide (Scheme 4.16).
10 % mol Co
2
(CO)
8
60 % mol Bu
3
PS
1atmCO
Ph
CO
2
Me
Ph
CO
2
Me
H
NR
O
NR
64
65
Scheme 4.16
An intramolecular Pauson-Khand reaction reported by Jinag.
In 2004, Saito
et al.
reported a novel diastereoselective total synthesis of isocarbacyclin
68
that features a fused bicyclic key intermediate obtained from L-ascorbic acid.
19
This inter-
mediate was prepared in multigram quantities via the Pauson-Khand reaction of L-ascorbic
acid-based (R)-4,4-diallyl-2,2-dimethyl-5-(trimethylsilyl)ethynyl-1,3-dioxolane
66
,bydis-
criminating between the diastereotopic groups and faces of the geminal allyl substituents.
The functional group assembly in
67
and the conventional synthetic reactions used for
the conversion of
67
to
68
makes this approach attractive for flexible access to side-chain
analogs of
68
(Scheme 4.17).
COOH
O
Co
2
(CO)
8
,CH
2
Cl
2
/
0°Ctort,3hthen
MeCN, 65 °C, 3 h (78 %)
O
O
O
H
H
H
OH
OH
TMS
66
O
67
Isocarbocyclin (68)
Scheme 4.17
Construction of key intermediate
67
via Pauson-Khand reaction.
An interesting use of PKR was reported by Jeong
et al.
, who studied the desym-
metrization of
meso
-dienynes such as propargyl 1-vinylallyl
N
-tosylamides
69a-c
and
propargyl 1-vinylallyl ethers
69d-e
using asymmetric Pauson-Khand-type catalysts
(Scheme 4.18).
20
The corresponding vinyl-substituted optically active N- or O-containing
bicyclo[3.3.0]octenes,
70
and
71
, were obtained with high diastereoselectivity (up to 75:1)
and good enantioselectivity (up to 81% ee)
