Page 9 - Volume 3, Issue 2, July 2010
Basic HTML Version
© Benaki Phytopathological Institute
Mosquito oviposition aggregation pheromone
39
mosquito pheromone.
Finally, it is noteworthy that in sever-
al cases, apart from the Wittig reaction and
the use of Grignard reagents, radical chain
reactions or organolithium substrates have
also been successfully employed for the
construction of the carbon skeleton.
2.1. Asymmetric syntheses from carbo-
hydrates
Several approaches to (–)-(5
R
,6
S
)-6-ace-
toxy-5-hexadecanolide have exploited car-
bohydrates as chiral starting materials. In
this regard, Kang and Cho (1989) published
an enantiospecific synthesis of (–)-(5
R
,6
S
)-6-
acetoxy-5-hexadecanolide,
1a
, from readily
available (–)-2-deoxy-
D
-ribose (Figure 6).
Acetonide
2
, prepared as an anomer-
ic mixture in ~60% yield from commercial
(–)-2-deoxy-
D
-ribose was condensed with
n
-
octyltriphenylphosphorane to give the un-
saturated alcohol
3
in a ratio Z/E ~ 9/1. Cat-
alytic hydrogenation on Pd/C provided the
saturated alcohol which was converted to
the iodide
4
. Elongation of the carbon skele-
ton was achieved by a radical chain reaction
of the iodide
4
with ethyl acrylate leading to
the condensed product
5
. Hydrolysis of es-
ter with potassium hydroxide, deprotection
of the acetonide, lactonization under acidic
conditions and acetylation of the semifinal
hydroxylactone afforded the target com-
pound
1a
(7 steps, 10% overall yield)
.
Ichimoto reported the synthesis of
(–)-(5
R
,6
S
)-6-acetoxy-5-hexadecanolide in
an enantiomerically pure form via the key
intermediate (+)-(
S
)-1-[(
R
)-oxiran-2-yl]unde-
can-1-ol,
6
, derived from 2-deoxy-D-ribose
(Figure 7) (Ichimoto
et al.
, 1988). Coupling
reaction of the hydroxyl protected prod-
uct of
6
with 3-butenylmagnesium bro-
mide and oxidative cleavage of the terminal
olefinic group afforded pyran derivative
8
,
which was oxidized with pyridinium dichro-
mate to give the desired lactone. Hydrolytic
cleavage of the THP group and subsequent
acetylation furnished
1a
(12 steps, from 2-de-
oxy-D-ribose, 12.7% overall yield)
.
A formal synthesis of
1a
from
D
-ribose
was reported by Gallos
et al.
(2000) based on
Figure 6
Figure 7
