© Benaki Phytopathological Institute
Mihou & Michaelakis
46
of hydroxylactone afforded natural oviposi-
tion attractant pheromone
1a
(
7 steps, 11%
yield
).
Couladouros andMihou (1999) published
a methodology of synthezing six membered
asymmetric lactones from
δ
-valerolactone
using the following reaction sequence: Re-
duction, Wittig-Schlosser coupling, Sharp-
less asymmetric dihydroxylation, oxidation
and lactonization. The offset of the synthe-
sis involved the
trans
olefinic substrate
57
as derived from the Wittig- Schlösser reac-
tion between the phosphonium salt of bro-
moundecane with 5-[(
t
-butyldiphenylsilyl)
oxy]pentanal (E/Z ratio 9/1). Application of
the Sharpless asymmetric dihydroxylation
protocol to substrate
57
furnished the opti-
cally pure diol. (5
R
,6
S
)-6-acetoxy-5-hexade-
canolide was prepared via a carbonate ester,
utilizing a novel lactonization with inversion
of stereochemistry (Figure 22) (
8 steps, 38%
yield
).
In 1990, Wu Y.-L. and Wu W.-L. achieved
the synthesis of
1a
in 10% overall yield start-
ing from (
S
)-
O
,
O
-isopropopylideneglycer-
aldehyde and in 35% overall yield starting
from (
R
)-
O
,
O
-isopropopylideneglyceralde-
hyde, using diastereoselective dihydroxyla-
tion (with catalytic amounts of OsO
4
) as the
key step (the ratio of the two isomers be-
ing about 9:1). When (
S)
-
O
,
O
-isopropopy-
lideneglyceraldehyde was used as the start-
ing material, the lipophilic side chain was
introduced after “late” lactone ring forma-
tion, whereas in the second case the lipo-
philic side was “early” introduced (Figure
23).
2.4. Chiral pool syntheses
The benzyl derivative of
S
-2-hydroxy-do-
decanal, prepared by a previously described
asymmetric synthesis based on a chiral
Figure 23
Figure 22
1...,6,7,8,9,10,11,12,13,14,15 17,18,19,20,21,22,23,24,25,26,...59