Page 13 - Volume 3, Issue 2, July 2010
Basic HTML Version
© Benaki Phytopathological Institute
Mosquito oviposition aggregation pheromone
43
ka (1983) employed the Sharpless asymmet-
ric epoxidation as the starting step. Kinetic
resolution of 1-tridecen-3-ol by enantiose-
lective epoxidation using diisopropyl tar-
trate gave an optically active epoxy alcohol
in good enantiomeric excess (91-94.5%
ee
).
A Grignard reagent prepared from 4-meth-
yl-3-pentenyl bromide was added to the ep-
oxide to effect the C-chain elongation. The
terminal double bond was oxidized to an
acid by the Sharpless modification of the
catalytic RuO
4
oxidation. Upon heating the
acid lactonized to give a
δ
-lactone. Acety-
lation of the lactone gave the final product
(Figure 15)
(9 steps, 33% yield).
Some years later, the same enantiomeri-
callypureepoxy alcohol
36
was employedby
Barua and Schmidt (1986) for their synthesis
.
Reaction of
β
-lithiated-
β
-ethylthioacrylate
with epoxide
36
and subsequent Raney
nickel treatment gave the oviposition pher-
omone
1a
(Figure 16)
(4 steps, 35% yield).
The synthesis of
1a
from readily available
1,2-cyclohexanediol using kinetic resolution
of cyclic allylic alcohol by modified Sharp-
less asymmetric epoxidation reagent as the
key step was reported by Wang
et al.
(1990)
(Figure 17). The asymmetric allylic alcohol
was initially converted to the silyl ether. Hy-
droboration of the silyl ether with 9-BBN fol-
lowed by alkaline hydrogen peroxide work-
up, yielded a mixture of the alcohol
42
and
its diastereoisomer in a ratio 2:1. After chro-
matographic separation, compound
42
was
oxidized with PDC to the corresponding ke-
tone. Beayer-Villiger oxidation of ketone,
followed by acetylation afforded the target
lactone
1a
(8 steps, 23% yield).
Bonini described the enantio- and ste-
reoselective synthesis of (–)-(5
R
,6
S
)-6-ace-
toxy-5-hexadecanolide via chemo-, regio-
and stereoselective opening with LiI of a
chiral epoxy alcohol precursor which was
obtained by kinetic resolution of the race-
mic allylic alcohol
44
(Figure 18) (Bonini
et
al.
, 1995). The resulting halohydrin was easi-
ly reduced to the corresponding
erythro
vic-
inal diol by
n
-Bu
3
SnH, which was then pro-
tected as acetonide. Oxidation with RuCl
3
,
lactonization with catalytic amount of
p
-
Figure 15
Figure 16
