Biomedical Engineering Reference
In-Depth Information
O
O
MnO
2
CH
2
Cl
2
, 0°C
O
O
O
OH
OH
H
OH
398
399
6
π
-Electrocyclization
O
O
HO
OH
OH
OH
O
O
O
O
vs.
O
O
O
O
O
O
400
401
401
401
endo
-
anti
(epoxide)-
anti
(Me)-hetero
exo
-
anti
(epoxide)-
anti
(Me)-homo
40%
25%
O
O
HO
HO
OH
OH
O
O
O
O
O
O
O
O
H
H
O
O
Epoxyquinol A
402
Epoxyquinol B
403
SCHEME 9.70
Synthesis of epoxyquinols A
402
and B
403
by Osada and coworkers.
derivatives
(Scheme 9.70). These two intermediates subsequently dimer-
ized via an intermolecular Diels-Alder reaction to afford epoxyquinol A (
400
and
401
402
) and
epoxyquinol B
in 40% and 25% yield, respectively. The mode of dimerization is
described as
endo
-
anti
(epoxide)-
anti
(Me)-hetero for compound
403
402
and
exo
-
anti
(epoxide)-
anti
(Me)-homo for compound
. Interestingly, the ratio of the two
compounds varies depending on the nature of the solvent.
Rollidecins C (
403
) are two polyether natural products isolated
from the leaf extracts of
Rollinia mucosa
. These annonaceous acetogenins have
antimalarial, immunosuppressive, and pesticidal activities. By applying the rhenium
(
VII
)-mediated domino oxidative polycyclization of homoallylic alcohols, Keinan and
coworkers devised a synthesis of these bis-furans [158]. In this instance, enantiopure
bis-homoallylic alcohols
406a
) and D (
406b
, when treated with CF
3
CO
2
ReO
3
and TFAA,
provided the desired bis-THF products
404a
or
404b
405a
405b
in 49% and 29% yields,
respectively (Scheme 9.71). As these transformations were both in the latter stages of
the syntheses, only one and two simple transformations, respectively, led to the
natural products
406a
and
406b
.
The pharmaceutical benefits of the CP molecules CP-263114 (
and
407
) and
CP-225917 (
) have been discussed earlier. Nicolaou and coworkers developed a
neat domino reaction using a Dess-Martin oxidation and exposure to air for the
preparation of their core structure by transforming 1,4-diol
408
413
(Scheme 9.72) [159]. The proposed intermediates in this transformation included
409
into bis-lactols
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