Page 14 - Volume 3, Issue 2, July 2010
Basic HTML Version
© Benaki Phytopathological Institute
Mihou & Michaelakis
44
TsOH and finally acetylation afforded lac-
tone
1a
(6 steps, 23% yield).
2.3.Syntheses via asymmetric epoxida-
tion or dihydroxylation reactions
All the four optical isomers of
Cx. quin-
quefasciatus
oviposition pheromone were
synthesized by Lin
et al.
(1985) via Sharp-
less asymmetric epoxidation protocol (Fig-
ure 19). The allylic alcohol, prepared from
propargylic alcohol by partial hydrogena-
tion, was exposed over Sharpless conditions
to give all the optically active epoxy alco-
hols. The (2
S
,3
S
)- isomer was treated with
Collins reagent to give the epoxy aldehyde
which after Wittig reaction led to the com-
plete construction of the carbon skeleton.
Oxidation of the free hydroxyl group to an
acid proceeded without affecting the chiral
epoxy moiety. The acid was then lactonized
in acidic conditions to form (5
R
,6
S
)-6-hy-
droxy-5-hexadecanolide with inversion of
the configuration at C5. Subsequent acety-
lation completed the synthesis of
1a
(9 steps,
15-20%
yield)
.
Singh and Guiry (2009) also used Sharp-
less asymmetric epoxidation reaction as one
of the key steps of their synthesis (Figure 20).
Figure 17
Figure 18
