Chloroglycidate synthesis of a precursor of natural 3-deoxy-D-manno- octulosonic acid with combined protective groups

Article abstract of DOI:10.1023/B:RUGC.0000025507.24993.c6

A new oxo form of D-mannose with cyclohexylidene and benzyl protective groups is synthesized with the aim of adapting the chloroglycidate synthesis for natural 3-deoxy-D-manno-octulosonic acid. The sites of fixation of the protective groups were establish

Full text of DOI:10.1023/B:RUGC.0000025507.24993.c6

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Russian Journal of General Chemistry, Vol. 74, No. 2, 2004, pp. 225 229. Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 2, 2004,
pp. 253 258.
Original Russian Text Copyright
2004 by Kornilov, Glebova, Turik, Bicherova, Zhdanov.
Chloroglycidate Synthesis of a Precursor
of Natural 3-Deoxy-D-manno-octulosonic Acid
with Combined Protective Groups
V. I. Kornilov, Z. I. Glebova, S. V. Turik, I. I. Bicherova, and Yu. A. Zhdanov
Research Institute of Physical and Organic Chemistry, Rostov State University, Rostov-on-Don, Russia
Received January 15, 2002
Abstract A new oxo form of D-mannose with cyclohexylidene and benzyl protective groups is synthesized
with the aim of adapting the chloroglycidate synthesis for natural 3-deoxy-D-manno-octulosonic acid. The
sites of fixation of the protective groups were established by converting a model compound, 4-O-acetyl-2,3:
5,6-di-O-cyclohexylidene-aldehydo-D-mannose, into a known dicyclohexylidene-D-manno-furanose. The oxo
form was reacted with methyl dichloroacetate to obtain a stereoisomeric mixture of chloroglycidates which
were transformed into the corresponding pyruvate. The ketone and enol forms of the latter compound were
isolated and separately characterized.
The chloroglicydate method we developed earlier
proved quite effective for synthesis of biologically
important natural 3-deoxyaldulosonic acids. Its ad-
vantages are stereoselectivity, availability of reagents,
ease to perform, and high yields in separate stages.
The method allows building on two carbon atoms to
the parent aldose, irrespective of the length or con-
figuration of the polyol chain. As a result, equally
successful syntheses of natural 3-deoxy-D-arabino-
heptulosonic [1] and 3-deoxy-D-glycero-D-galacto-
nonulosonic [2] acids could be accomplished. Ho-
wever, 3-deoxy-D-manno-octulosonic acid, one of the
most important representatives of this series of car-
boxydrate derivatives, falled outside the scope of this
method. Nevertheless, the adaptation of the chloro-
glycidate synthesis for octulosonic acid would add to
its versatility.
mannose diethyl dithioacetal (II) (yield 42%) which
exhibits the greatest chromatographic mobility. The
structure of the product was confirmed by its acetyla-
tion in standard conditions in the presence of pyridine
to obtain 4-O-acetyl-2,3:5,6-di-O-cyclohexylidene-
D-mannose diethyl dithioacetal (III). The latter was
hydrolyzed in the presence of mercury(II) chloride to
give 4-O-acetyl-2,3:5,6-di-O-cyclohexylidene-al-
dehydo-D-mannose (IV). Finally, the position of the
acetyl group, and, consequently, of the cyclohexyl-
idene protections, was confirmed by the transforma-
tion of al form IV into a known 2,3:5,6-di-O-cyclo-
hexylidene-D-manno-furanose (V) [4] upon Zemplen
deacetylation.
The above-described experiment gave clear evi-
dence for the positions of the cyclohexylidene groups
but failed to provide an appropriate aldose for the
chloroglycidate synthesis because of the lability of
the acetyl group in alkaline media.
The indispensable requirement for the scheme to
work is that an aldose with alkali-resistant protective
groups be present. The syntheses of heptulosonic and
nonulosonic acids were based on a pentose and
heptose with even numbers of hydroxy groups, in
view of which fully acetylated derivatives were
brought in reaction. The synthesis of octulosonic acid
should be started with D-mannose whose acetylation,
like with other hexoses, is not a single-route reaction.
From this it follows that the prevailing isomer should
be isolated to find out the site of alkylidene protective
groups and to additionally protect the free hydroxy
group. In [3] we found that the prevailing acetalation
product of D-mannose diethyl dithioacetal (I) with
cyclohexanone is 2,3:5,6-di-O-cyclohexylidene-D-
CH(SEt)2
CH(SEt)2
HO
HO
O
O
Ch
OH
OH
OH
OR
O
O
Ch
I
II, III, VI
CH=O
O
O
O
O
Ch
Ch
O
OR
O
O
Ch
Ch
.
O
O
.
..
OH
IV, VII
V
R = H (II), Ac (III, IV), Bn (VI, VII).
1070-3632/04/7402-0225 2004 MAIK Nauka/Interperiodica

226
KORNILOV et al.
In this connection we consider it more perspective
acetate with sodium hydride; concurrently, the alk-
oxide ion attacks the C Cl bond, cleaving chlorine.
From general considerations, the reaction should give
a stereoisomeric product mixture, but when synthesiz-
ing 3-deoxy-D-arabino-heptulosonic and 3-deoxy-L-
xylo-heptulosonic [6] acids, we isolated from the re-
action mixture only one isomer, whereas with non-
ulosonic acid, a 3:1 mixture.
to protect the C4 OH group in acetal II by benzyla-
tion, which assures both stability of the aldose and
deprotection. Benzylation of dicyclohexylidene deri-
vative II in standard conditions (excess benzyl chlo-
ride, NaOH powder, p-xylene, 105 C) is accompanied
by strong tarring and formation of by-products (for
instance, dibenzyl), thus requiring multiple and
thorough chromatographic purification and adversely
affecting the yield of benzylate VI (55 58%). Milder
benzylation conditions (sodium hydride, dimethylform-
amide, room temperature) [5] allowed the yield of a
chromatographically pure product to be improved to
83%. The conversion of thioacetal VI into 4-O-benzyl-
2,3:5,6-di-O-cyclohexylidene-aldehydo-D-mannose
(VII) with HgO HgCl2 in aqueous acetone occurs
quantitatively, and the product needs no purification
for further reactions. The IR spectrum of compound
The same as the latter result was obtained with
methyl 2,3-anhydro-O-benzyl-2-chloro-6-4,5:7,8-di-O-
cyclohexylidene-D-manno-octonate (VIIIa, VIIIb)
which was isolated as a chromatographically homo-
geneous substance (yield 40%). Indirect evidence
showing that it is an isomeric mixture of VIIIa and
VIIb with prevalence of one isomer was provided by
the observation in the 1H NMR spectrum of two
strong closely located methoxyl proton signals at
3.8 ppm. The signal of the epoxide proton at C3,
which reliably indicates whether one deals with an
isomeric mixture or with a completely acetalated
derivative ( 3.5 ppm), is shifted downfield to fall into
a region saturated with skeletal proton signals (
3.7 ppm) as a result of deshieliding produced by the
aromatic nucleus of the benzyl protection. Along with
1
VII shows aromatic ring (1600 cm ) and carbonyl
1
(1735 cm ) absorption. The 1H NMR spectrum
contains signals of cyclohexylidene methylene protons
at 1.3 and 1.5 ppm, benzyl methylene protons at
4.7 ppm, as well as aromatic ring ( 7.3 ppm) and
aldehyde protons ( 9.6 ppm).
1
Aldehyde VII was introduced into the chloro-
glycinate synthesis with methyl dichloroacetate.
Chloroglycidate formation occurs as nucleophilic
addition of a carbanion generated from methyl chloro-
the above signals, the H NMR spectrum of the pro-
tections at 1.3 and 1.5 ppm, and the IR spectrum
shows absorption bands of the aromatic ring at
1
1600 cm 1 and of the carbonyl group at 1750 cm .
CO2Me
CO2Me
O
CH=O
CO2Me
Cl
~
O
CCl2CO2Me
Ch
Cl
H
Cl
H
+
O
O
Cl
NaH
OBn
C
~~~
O ~~~
H
O
~
~
Ch
~
O
VII
CO2Me
O MgI
Cl
VIIa
VIIb
CO2Me
C OH
CO2Me
C OAc
CO2Me
C=O
Ac2O
Py
H2O, NaHSO3
MgI2
+
CH
~
IXb
CH
~
CH2
~
IXa
CHI
~
X
In view of our present and published data, we can
draw certain conclusions as to the stereochemistry of
the reaction studied. According to a commonly ac-
cepted notion based on Felkin models, aldose VII
prefers a conformation whose fragment is shown
below. The nucleophilic attack on carbonyl occurs
from the least shielded side, i.e. it is antiperiplanar
with respect to the heaviest substituent (polyol
residue). As a result, an anion with erythro-configured
C3 and C4 is formed, thus giving rise to the prevailing
isomer VIIIb with the same configuration of these
carbon centers.
The fact that chloroglycidates are formed as an
isomeric mixture has no effect on the final stereo-
chemical result, since C2 and C3 get achiral already in
the next stage.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 2 2004

CHLOROGLYCIDATE SYNTHESIS OF A PRECURSOR
227
optical activities were measured on a Hilger-412M
polarimeter in CHCl3. Silokhrom C-80 (fraction 0.1
0.2) and Al2O3 (chromatographic grade) were used
as sorbents.
CO2Me
CO2Me
CCl2
H
== O
CCl2
H
O
H
O
O
C
H
2,3:5,6-Di-O-cyclohexylidene-D-mannose diethyl
dithioacetal (II). Cyclohexanone, 30 ml, anhydrous
dioxane, 10 ml, and 5 ml of conc. H2SO4 were added
one after another to 18 g of thioacetal I with stirring.
Heat release was observed, and the mixture got dark.
After 2-h stirring at room temperature, the mixture
was left to stand for 12 h, diluted with 100 ml of
CHCl3, and poured into excess water. The chloroform
layer was separated, washed with water to neutral
washings, dried with Na2SO4, and the solvent was
removed. The residue was dissolved in petroleum
ether, applied to a column of SiO2, most cyclo-
hexanone was eluted with petroleum ether, and the
most mobile reaction product, with petroleum ether
benzene, 1:2. The solvent was removed, and the
residue was further purified on a column of Al2O3,
eluent CHCl3. Yield 11.8 g (42%), syrup, Rf 0.7
C
To convert chloroepoxide into pyruvate, the
oxirane ring was cleaved with MgI2 etherate followed
by hydrolysis and reduction of the intermediate iodine
derivative with saturated sodium bisulfite in one
pot. The coversion was almost quantitative, and the
chromatographically homogeneous band of pyruvate
was separated into two fractions by crystallization
from petroleum ether. The first fraction is a crystalline
compound (yield 62%, mp 113 115 C) and the
second is a syrup (isolated in 21% yield from the
filtrate and additionally purified on a column of
Silokhrom). By 1H and IR spectroscopy the com-
pounds were characterized as the ketone (compound
IXa) and enol (compound IXb) forms of the starting
pyruvate. The IR spectrum of the syrup-like keto ester
(Al2O3, CHCl3), [ ]D8 4.15 (c 1.9). H NMR spec-
1
1
trum (CCl4), , ppm: 1.4 d (26H, 2C6H10, 2CH3),
2.7 m (4H, 2SCH2), 3.9 4.4 m (7H, H2 H6,6 , OH,
5.25 s (1H, SCHS). Found, %: C 57.12; H 8.70; S
14.46. C22H38O5S2. Calculated, %: C 56.95; H 8.52;
S 14.34.
IXa shows aromatic ring absorption at 1600 cm and
1
1
carbonyl absorption near 1725 cm . In the H NMR
spectrum, along with signals characteristic of the
protective and methoxy groups, there is a multiplet
two-proton signal of the deoxy unit at C3 ( 3.2 ppm),
which is characteristic of deoxy saccharides. The IR
spectrum of the crystalline enol IXb contains aromatic
4-O-Acetyl-2,3:5,6-di-O-cyclohexylidene-D-
mannose diethyl dithioacetal (III). Anhydrous
pyridine, 3 ml, and 6 ml of acetic anhydride were
added to 1.1 g of acetal II. The mixture was left to
stand at room temperature for 12 h and poured into
cold water, stirred for 2 h, treated with three portions
of CHCl3, the chloroform extracts were combined,
washed with dilute H2SO4 to remove pyridine and
then with water to netral washings, dried with Na2SO4,
and the solvent was removed. The residue was tritu-
rated with 10 15 ml of 70% CH3COOH and refri-
gerated for 12 h, after which the semisolid material
was again thoroughly triturated until it crystallized.
The crystals were filtered off and recrystallized from
2-propanol. Yield 3.5 g (73%), mp 65 66 C, 64 C
(from 2-propanol), Rf 0.9 (Al2O3, CHCl3), [ ]8D +5.0
1
1
ring (1620 cm ), C=C (1680 cm ), conjugated ester
1
1
carbonyl (1715 cm ), and OH (3400 cm ) absorption
bands. In the 1H NMR spectrum of compound IXb we
observe characteristic doublet of the vinyl proton at
5.8 ppm and singlet of the hydroxyl proton at
6.25 ppm. Pyruvate IXa, IXb was additionally cha-
racterized as enol acetate X obtained in standard
acetylation conditions (Ac2O Py) in 46% yield after
chromatographic purification. Its IR spectrum contains
1
signals of the double bond (1670 cm ) and methoxy-
carbonyl (1740 cm ) and conjugated acetoxy groups
1
1
(1765 cm ), characteristic of enol acetates. In the H
NMR spectrum, acetyl protons appear as a singlet
near 2.1 ppm and the vinyl proton, as a doublet at
6.6 ppm. Thus, we have synthesized pyruvate IX
which can be converted into 3-deoxy-D-manno-
octulosonic acid via saponification of the ester group,
deacetalation, and debenzylation [1, 2, 7, 8].
1
(c 0.54). H NMR spectrum, , ppm: 1.4 d (26H,
2C6H10, 2CH2CH3), 2.1 s (3H, COCH3), 2.7 m (4H,
2SCH2), 3.9 4.4 m (5H, H2, H3, H5, H26), 5.25 m (2H,
SCHS, H4). Found, %: C 58.89; H 8.30; S 13.27.
C24H40O6S2. Calculated, %: C 59.02; H 8.19; S 13.11.
EXPERIMENTAL
4-O-Acetyl-2,3:5,6-di-O-cyclohexylidene-al-
dehydo-D-mannose (IV). To a solution of 4.8 g of
acetal III in 30 ml of acetone we added 2.5 ml of
water and, with vigorous stirring, 5 g of yellow HgO
and 5 g of HgCl2. The mixture was stirred for 3 h at
The IR spectra were recorded on a Specord IR-75
spectrophotometer in thin films. The H NMR spectra
1
were obtained on
a
Unity-300 spectrometer
(300 MHz) in CDCl3, internal reference TMS. The
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 2 2004

228
KORNILOV et al.
40 C and for 20 min at 50 C. Most mercury salts
were filtered off and washed on the filter with water.
The filtrate was evaporated to dryness. Chloroform,
30 ml, was added to the residue and then decanted
(the procedure was repeated 3 times). The chloroform
solutions were combined, washed with 1 N KI and
two portions of water, and dried with Na2SO4. The
solvent was removed, and the syrup-like residue was
subjected to column chromatography on SiO2 in
chloroform. Yield 1.4 g (38%), Rf 0.2 (SiO2, CHCl3),
at room temperature. After 6 h (control by chromato-
graphy), 50 ml of CHCl3 was added to the mixture,
and it was filtered. The filtrate was washed with 1 N
KI and water, and dried with CaCl2. The solvent was
removed in a vacuum. The reaction product was
purified on a column of Silokhrom (CHCl3), yield
1.02 g (98%), syrup, Rf 0.4 (Al2O3, CHCl3). IR spec-
trum, , cm : 1735 (C=O), 1590, 1600 (C6H5). H
NMR spectrum, , ppm: 1.3 1.5 m (20H, C6H10),
3.9 4.1 m (5H, H3 6,6 ), 4.3 m (1H, H2), 4.7 m (2H,
OCH2C6H5), 7.2 7.4 m (5H, C6H5), 9.6 s (1H,
CH=O). Found, %: C 69.22; H 8.30. C25H34O6.
Calculated, %: C 69.77; H 7.91.
1
1
[ ]8D 11.6 (c 1.12). IR spectrum, , cm : 1730
1
1
(CH=O), 1750 (OCOCH3). H NMR spectrum,
ppm: 1.5 s (20H, 2C6H10), 2.15 s (3H, COCH3), 3.9
,
4.4 m (5H, H2, H3, H5, H26), 5.3 d (1H, H4), 9.6 s (1H,
CH=O). Found, %: C 53.08; H 7.96. C20H30O7.
Calculated, %: C 62.82; H 7.85.
Methyl 2,3-anhydro-6-O-benzyl-2-chloro-4,5:
7,8-di-O-cyclohexylidene-D-manno-octonate (VIIIa,
VIIIb). To an ice-cold solution of 1.3 g of aldose VII
and 0.51 ml of methyl dichloroacetate in 6 ml of an-
hydrous benzene and 2 ml of DMF we added in por-
tions with vigorous stirring 0.24 g of NaH (60%
suspension in mineral oil). Each following portion of
sodium hydride was added when hydrogen evolution
had ceased. After all sodium hydride had been added,
the mixture was cooled with ice for an additional
0.5 h and then left to stand at room temperature for
12 h. Therewith, the mixture got dark. It was poured
into cold water (10 ml) acidified with dilute hydro-
chloric acid, the benzene layer was separated, and the
aqueous solution was treated with benzene (3.5 ml).
The combined benzene extracts were washed with
water to neutral washings, dried with CaCl2, and the
solvent was removed in a vacuum. The residue was
subjected to column chromatography on SiO2, yield
1.4 g (86%), syrup, Rf 0.5 (SiO2, CHCl3). IR spectrum,
2,3:5,6-Di-O-isopropylidene-D-manno-furanose
(V). Sodium methoxide (0.2 ml, 2 N solution) was
added to a solution of 0.5 g of aldose IV in 2 ml of
anhydrous methanol. The mixture was refrigerated for
12 h, poured into water, and the reaction poduct was
extracted with chloroform (3.5 ml). The chloroform
extracts were washed with water to neutral washings,
dried with Na2SO4, and the solvent was removed. The
syrup-like residue was crystallized from petroleum
ether, mp 120 121 C (from petroleum ether ethanol,
10:1) {cf. [4]: mp 122 C (from hexane)}.
4-O-Benzyl-2,3:5,6-di-O-cyclohexylidene-D-
mannose diethyl dithioacetal (VI). Sodium hydride
(0.44 g, 60% suspension in mineral oil) was added in
portions with stirring to a solution of 1.1 g of thio-
acetal II in 26 ml of anhydrous DMF. After 45 min,
88 ml of benzyl chloride was added dropwise. The
mixture was left to stand for 12 h at room temperature
and then poured into 150 ml of cold water acidified
with dilute HCl. The reaction product was extracted
with benzene (3.15 ml). The combined benzene
extracts were washed with water to neutral washings,
dried with Na2SO4, and the solvent was removed in
a vacuum. The residue was subjected to column
chromatography on a column of Al2O3 in benzene
hexane, 1:1. Yield 1.15 g (88%), syrup, Rf 0.8
1
1
, cm : 1500, 1560, 1620 (C6H5), 1750 (C=O). H
NMR spectrum, , ppm: 1.3, 1.5 m (20H, C6H10),
3.7 4.3 m (10H, OCH3, H3 8,8 ), 4.8 m (2H, OCH2
C6H5), 7.3 m (5H, C6H5). Found, %: C 62.33; H 7.21;
Cl 6.18. C28H37ClO8. Calculated, %: C 62.63; H 6.89;
Cl 6.62.
Methyl 6-O-benzyl-4,5:7,8-di-O-cyclohexyl-
idene-3-deoxy-D-manno-octulosonate (IXa, IXb).
Finely ground iodine, 1.07 g, was added in portions
with stirring to a solution of methylmagnesium iodide,
obtained from 0.26 ml of methyl iodide and 0.11 g of
magnesium turnings in 10 ml of anhydrous diethyl
ether, until the light yellow color no longer dis-
appeared. A solution of 0.84 g of epoxide VIII in
10 ml of diethyl ether was added dropwise to the
resulting magnesium iodide etherate. Heat release was
observed, and the mixture got dark. It was stirred
under reflux for 30 min, diluted by half with water,
transferred into a separatory funnel, and treated with
saturated sodium bisulfite (added in small portions)
until stramineous. The organic layer was separated,
1
(Al2O3, CHCl3). IR spectrum, , cm : 1600 (C6H5).
1H NMR spectrum, , ppm: 1.22 t, 1.27 t (6H,
2SCH2CH3), 1.35 1.55 m (20H, C6H10), 2.7 m (4H,
2CH2S), 3.8 4.3 m (6H, H2 6,6 ), 4.7 d, 4.95 d (2H,
OCH2C6H5), 7.3 m (6H, H1, C6H5). Found, %: C
64.56; H 8.61; S 11.42. C29H44O5S2. Calculated, %:
C 64.92; H 8.20; S 11.94.
4-O-Benzyl-2,3:5,6-di-O-cyclohexylidene-al-
dehydo-D-mannose (VII). Thioacetal VI, 1.3 g, was
mixed with 1.6 g of yellow HgO and 1.6 g of HgCl2
in a mixture of 6.5 ml of acetone and 0.6 ml of water
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 2 2004

CHLOROGLYCIDATE SYNTHESIS OF A PRECURSOR
229
the aqueous layer was treated with chloroform (4
2.1 s (3H, COCH3), 3.6?4.7 m (11H, OCH3, H4 8,8
,
OCH2C6H5), 6.6 d (1H, HC=C), 7.25 m (5H, C6H5).
Found, %: C 66.92; H 7.61. C30H40O9. Calculated,
%: C 67.28; H 7.35.
10 ml), the combined extracts were washed with water
until neutral washings, dried with CaCl2, and the sol-
vent was removed in a vacuum. The residue was
crystallized from petroleum ether or hexane to isolate
enol IXb, yield 0.4 g (51%), mp 113 115 C, Rf 0.6
ACKNOWLEDGMENTS
(SiO2, CHCl3). IR spectrum (1% solution in CHCl3),
1
The work was financially supported by the Russian
Foundation for Basic Research (project no. 99-03-
32985) and the Basic Research of High School in
Natural and Humanitary Sciences. University of
, cm : 1620 (C6H5), 1680 (C=C), 1715 (C=O), 3400
1
(OH). H NMR spectrum, , ppm: 1.3, 1.5 m (20H,
C6H10), 3.65 4.7 m (11H, OCH3, H4 8, OCH2C6H5),
5.8 d (1H, CH=C), 6.25 s (1H, OH), 7.3 m (5H,
C6H5). Found, %: C 66.40; H 8.02. C28H38O8. Cal-
culated, %: C 66.93; H 7.55.
1
Russia Program (project no. 991440). The H NMR
spectra were measured in the North-Caucasus Center
for Collective Use, Russian Foundation for Basic
Research.
Ketone IXa was isolated from the mother liquor
and purified on a column of SiO2. The starting
epoxide was eluted with benzene, and the reaction
product, with chloroform. Yield 0.33 g (42%), syrup,
REFERENCES
1
1. Kornilov, V.I., Bicherova, I.I., Turik, S.V., and Zhda-
Rf 0.6 (SiO2, CHCl31). IR spectrum, , cm : 1620
nov, Yu.A., Bioorg. Khim., 1988, vol. 14, no. 7, p. 938.
(C6H5), 1725 (C=O). H NMR spectrum, , ppm: 1.3,
1.5 m (20H, C6H10), 3.2 m (2H, H3,3 ), 3.5 4.7 m
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(11H, OCH3, H4 8,8 , OCH2C6H5), 7.25 (5H, C6H5).
Found, %: C 66.59; H 7.86. C28H38O8. Calculated,
%: C 66.93; H 7.55.
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Methyl 2-O-acetyl-6-O-benzyl-4,5:7,8-di-O-
cyclohexylidene-3-deoxy-D-manno-2-octenate (X).
Acetic anhydride, 0.5 ml, was added to a cold solution
of 0.2 g of pyruvate IXa, IXb in 0.5 ml of anhydrous
pyrudune. The mixture was left to stand for 20 h at
5 C and poured into water with ice. When the an-
hydride had decomposed (1 2 h), the reaction product
was extracted with chloroform, the combined chloro-
form extracts were washed with dilute sulfuric acid to
remove pyridine and then many times with water to
neutral washings. The solvent was removed, and the
residue was subjected to chromatography on Al2O3
in chloroform. Yield 0.1 g (46%), syrup, Rf 0.6
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1
(Al2O3, C6H6 CHCl3, 1:1). IR spectrum, , cm :
8. Hengeveld, J.E., Grief, V., Tadanier, J., Lee, M.,
1
1670 (C=C), 1740 (CO2CH3), 1765 (OCOCH3). H
Riley, D., and Lartey, P.A., Tetrahedron Lett., 1984,
NMR spectrum, , ppm: 1.3, 1.5 m (20H, C6H10),
vol. 25, no. 37, p. 4076.
‘
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 2 2004