Hepta(methoxycarbonyl)cycloheptatriene halo derivatives

Article abstract of DOI:10.1007/s11172-015-0851-4

A reaction of potassium hepta(methoxycarbonyl)cycloheptatrienide with chlorine and bromine gave high yields of the corresponding chloroand bromohepta(methoxycarbonyl)cycloheptatrienes; the fluoro derivative was obtained by the exchange reaction of the corresponding bromide with silver fluoride. In contrast to the mentioned halides, the iodo derivative has proved unstable. Thermolysis of bromohepta(methoxycarbonyl)cycloheptatriene was studied, as well as its conversion to the azido and methoxy derivatives upon treatment with NaN₃ or methanol.

Full text of DOI:10.1007/s11172-015-0851-4

Russian Chemical Bulletin, International Edition, Vol. 64, No. 1, pp. 241—245, January, 2015
241
Hepta(methoxycarbonyl)cycloheptatriene halo derivatives
D. N. Platonov, G. P. Okonnishnikova, A. A. Levina,a and Yu. V. Tomilov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6390. Eꢀmail: tom@ioc.ac.ru
A reaction of potassium hepta(methoxycarbonyl)cycloheptatrienide with chlorine and broꢀ
mine gave high yields of the corresponding chloroꢀ and bromohepta(methoxycarbonyl)ꢀ
cycloheptatrienes; the fluoro derivative was obtained by the exchange reaction of the correꢀ
sponding bromide with silver fluoride. In contrast to the mentioned halides, the iodo derivative
has proved unstable. Thermolysis of bromohepta(methoxycarbonyl)cycloheptatriene was studꢀ
ied, as well as its conversion to the azido and methoxy derivatives upon treatment with NaN3 or
methanol.
Key words: potassium hepta(methoxycarbonyl)cycloheptatrienide, hepta(methoxycarbonꢀ
yl)cycloheptatriene halides, nucleophilic substitution, thermolysis.
In recent years, we have been interested in the explorꢀ
ing a possibility of a conjugation effect in the cycloꢀ
heptatriene system, whose electron density is substantially
decreased because of the presence of seven electronꢀwithꢀ
drawing ester substituents. In this system, the only hydroꢀ
gen atom exhibits a high acidity, whereas a formed anion
is very stable. In this case, in a counterpoise to the antiarꢀ
omatic character of the cycloheptatrienyl anion, the deloꢀ
calization effect of the negative charge over the ester groups
is a stabilizing factor. In fact, the Xꢀray diffraction data
show that in the hepta(methoxycarbonyl)cycloheptatrienyl
anion (1), the sevenꢀmembered ring is somewhat flattened,
the nearest to the anionic center double bonds are elonꢀ
gated and the single bonds are shortened, that indicates
a partial conjugation of the carbocycle five C atoms with
a delocalization of the negative charge over the oxygen
atoms of the ester groups.1 In this case, one of the double
bonds is not involved in the conjugation system and conꢀ
siderably deviates from the plane of the fiveꢀcarbon part of
realized in the case of the replacement of the proton with
a halogen atom. In this case, it becomes possible to generꢀ
ate substituted tropylium cation and to endow molecule
with a new type of reactivity.
It is known5 that penta(methoxycarbonyl)cyclopentaꢀ
diene anion can be easily involved in the reaction with
molecular bromine and chlorine, with the compounds obꢀ
tained serving as halogenation agents (they oxidize the
iodide anion and halogenate phenols), that indicates
a strong polarization of the C—Hal bond. It appears that
K[1] similarly easy reacts with molecular halogens. The
reaction was carried out by the addition of an acetonitrile
solutions of bromine or iodine to the acetonitrile solution
of K[1], whereas chlorine gas was purged through the soluꢀ
tion in the case of chloro derivative. Judging from the
disappearance of a characteristic crimson color of the anꢀ
ion, the reaction at 20 C is completed virtually instantly
and in the case of chlorine and bromine leads to the correꢀ
sponding halo derivatives 2a,b as colorless crystalline comꢀ
pounds in virtually quantitative yields (Scheme 1).
The structure of halides 2a,b was confirmed by Xꢀray
diffraction data (Fig. 1). In both compounds, a slight
elongation of the C(1)—C(2) and C(1)—C(7) bonds
(d = 0.1523—0.1527 nm) as compared to HMCH was
observed,1 with the C—Cl and the C—Br bond distances
being 0.1802 and 0.1965 nm, respectively, which is someꢀ
what longer than in the halohydrocarbons (0.1782 and
0.1938 nm, respectively).
1
the ring. At the same time, H and 13C NMR data show
that in solutions no any differences in the C—CO2CH3
fragments are observed, that indicates a rapid averaging
dynamics of these fragments in anion 1. In this connecꢀ
tion, anion 1 not only can react as Cꢀ or Oꢀnucleophile1,2
with electrophiles, but also might exhibit electrophilic
properties, which, for example, are observed in the reacꢀ
tions with primary amines.3,4 In most cases, these transꢀ
formations are accompanied by considerable changes in
the carbon skeleton.
In comparison with hepta(methoxycarbonyl)cycloꢀ
heptatriene (HMCH, H[1]), the same system but with an
alternative distribution of electron density is of a certain
interest. Such an approach, in particular, could have been
Fluoride 2c was synthesized by the exchange reaction:
silver fluoride was added to a solution of bromide 2b in
acetonitrile and after precipitation of insoluble silver broꢀ
mide (~4 h), fluoride 2c was obtained in quantitative yield
(see Scheme 1).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 0241—0245, January, 2015.
1066ꢀ5285/15/6401ꢀ0241 © 2015 Springer Science+Business Media, Inc.

242
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 1, January, 2015
Platonov et al.
Scheme 1
An interesting fact was found when analyzing the
1H and 13C NMR spectra of these compounds. At room
temperature, a considerable broadening was observed for
some signals of the methoxy groups in the 1H NMR specꢀ
tra of compounds 2a and 2b. When the sample is heated to
1
50 C or cooled to –20 C, these signals in the H NMR
spectrum become narrower (Fig. 2). Most likely, this
fact can be explained by two dynamic processes observed
at different temperatures: a retardation of the rotation
of the ester groups and the migration of the halogen
atom over the atoms of the sevenꢀmembered ring, similꢀ
arly to that observed in the case of thiophenylcycloꢀ
heptatrienes.6
Similar pattern was also observed in the 13C NMR
spectra. Thus, at room temperature for both chloroꢀ (2a)
and bromoꢀsubstituted HMCH (2b), the signals for the
quaternary carbon atoms of the sevenꢀmembered ring are
strongly broadened and virtually cannot be seen. Upon
heating of 2b to 50 C, a single narrow signal is clearly
observed in the region of olefin C atoms at  136. Conꢀ
versely, upon cooling of the sample to –30 C all three
expected signals appear in the 13C NMR spectrum. In this
case, the signals at  126 and 144, which at 50 C are
barely seen because of the strong broadening, become narꢀ
row enough, while the signal at  136 considerably broadꢀ
ens. Besides, at –30 C a second set of all the signals
appears in the 1H and 13C NMR spectra, that, apparently,
corresponds to the registration of both possible conformꢀ
ers due to the hindered inversion of the nonplanar configꢀ
uration of the sevenꢀmembered ring. The ratio of these
signals is ~5 : 1 and does not change upon reduction of the
sample temperature to –60 C.
E = CO2Me; X = Cl (a), Br (b)
a
C(17)
C(6)
C(15)
O(8)
O(9)
O(10)
C(16)
C(14)
O(7)
O(11)
C(18)
C(5)
C(9)
C(19)
C(4)
O(5)
C(12)
O(12)
C(8)
O(1)
C(7)
C(3)
O(2)
C(20)
O(14)
C(2)
C(1)
O(6)
C(13)
C(10)
C(21)
O(13)
O(4)
Cl(1)
In the case of iodine, all the attempts to obtain the
product similar to halides 2a—c were unsuccessful, with
methyl benzenehexacarboxilate (3) being the only isolable
reaction product.7 The cycloheptatrienyl derivative was
not detected even by lowꢀtemperature NMR spectroscopy;
when the reaction was carried out at –30 C, only the
signal for benzenehexacarboxylate 3 was clearly detected
O(3)
C(11)
b
C(17)
C(15)
O(7)
O(8)
O(10)
1
O(9)
in the H NMR spectra and no other informative signals
were observed.
C(16)
O(11)
C(18)
C(14)
C(4)
It appears that a similar process takes place also upon
reflux of bromide 2b in benzene for several hours. Under
these conditions, it decomposes with the formation of benꢀ
zenehexacarboxylate 3, however, we failed to intercept
a residual fragment of molecule 2b, which formally correꢀ
sponds to the carbene particle :CBrCO2Me, using differꢀ
ent unsaturated compounds (styrene, methyl acrylate).
Apparently, the formation of benzenehexacarboxylate reꢀ
sults from the disintegration of unstable hepta(methꢀ
oxycarbonyl)tropylium formed from compound 2b at eleꢀ
vated temperatures.
C(5)
O(5)
O(6)
C(19)
C(12)
C(3)
C(6)
C(9)
O(2)
O(12)
O(1)
C(7)
C(20)
O(14)
C(1)
C(13)
C(2)
C(10)
O(4)
O(13)
C(21)
Br(1)
O(3)
C(11)
The reaction of bromide 2b with primary amines
(benzylamine, 2ꢀethoxyethylamine) gave benzenehexacꢀ
arboxylate 3 and HMCH itself as the identified reacꢀ
Fig. 1. General view of molecules 2a (a) and 2b (b) in represenꢀ
tation of atoms by thermal ellipsoids.

Halohepta(methoxycarbonyl)cycloheptatrienes
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 1, January, 2015
c d
243
a
b
4.0 3.9 3.8 3.7 3.6
4.0 3.9 3.8
3.7 3.6
4.0 3.9 3.8 3.7 3.6
4.0 3.9 3.8 3.7 3.6

Fig. 2. 1H NMR spectra of chloro derivative 2a in CDCl3 at different temperatures: –30 C (a), –10 C (b), 25 C (c), 50 C (d).
tion products. The formation of the latter indicates that
bromide 2b can also serve as a brominating agent, as it
takes place in the case of 1ꢀbromoꢀ1,2,3,4,5ꢀpentaꢀ
(methoxycarbonyl)cyclopentaꢀ2,4ꢀdiene.5 Nonetheless,
we accomplished a formal nucleophilic substitution of
bromine in compound 2b with retention of the sevenꢀmemꢀ
bered ring in the reaction of bromide 2b with sodium azide
in methanol. In this case, we detected both the primary
reaction products, which were the corresponding azide 4,
and its decomposition products, benzenehexacarboxylate 3
and methyl cyanoformate slowly formed even at room
temperature (Scheme 2). Because of the low stability of
the azide, we failed to isolate it in the pure form, however,
the 1H and 13C NMR spectra and mass spectrometric data
clearly indicated its formation.
The observed decomposition of azide 4 differs from
the behavior of the suggested 1ꢀazidoꢀ1,2,3,4,5ꢀpentaꢀ
(methoxycarbonyl)cyclopentadiene, which decomposed
at room temperature with the liberation of nitrogen acꢀ
companied by the 1,2ꢀshift of the methoxycarbonyl subꢀ
stituent from carbon atom to the nitrogen atom with to
form the corresponding Nꢀmethoxycarbonyliminocycloꢀ
pentadiene.8
The substitution of bromine in compound 2b with
a methoxy group takes place upon reflux in methaꢀ
nol. Besides the formation of methoxy derivative 5, the
Scheme 2
E = CO2Me

244
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 1, January, 2015
Platonov et al.
Parameters for compound 2a: a = 8.9473(8) Å, b = 34.699(3) Å,
reaction gives benzenehexacarboxylate 3 and HMCH
approximately in the equal ratio and in up to 50% overall
yield (see Scheme 2). At room temperature, all the methꢀ
3
c = 7.9931(7) Å, V = 2413.5(4) Å , dcalc = 1.466 g cm–3; for
compound 2b: a = 9.0035(9) Å, b = 34.687(4) Å, c = 7.9689(8) Å,
3
V = 2416.3(4) Å , dcalc = 1.587 g cm–3. Atomic coordinates and
1
oxy groups in the H NMR spectrum of compound 5 are
full crystallographic informationя were deposited with the Camꢀ
bridge Structural Database (CCDC 1023830 and CCDC 1023828
for 2a and 2b, respectively). Hepta(methoxycarbonyl)cycloheptꢀ
atriene (HMCH) and potassium hepta(methoxycarbonyl)cycloꢀ
heptatrienide K[1] were synthesized according to the described
procedures.1 Solvents of the reagent grade (>99.5%) were used
without additional purification.
found as three broad signals with the ratio of integral inꢀ
tensities of 1 : 6 : 1. Upon cooling of the sample to –30 C,
the signals become narrower and the central signal "splits"
into three singlet signals of equal intensities.
Unfortunately, our attempts to increase the yield of
compound 5 failed. Though running the reaction in 85%
aqueous methanol significantly shortened the reaction time
(from 20 h for anhydrous methanol to 4 h), the yield of
compound 5 in this case was no more than 30%. This can
be explained either by the formation of unstable hydroxy
derivative of HMCH, or by the decomposition of 5 upon
treatment with HBr and traces of water. Relatively low
yield of compound 5 was also observed when the reaction
was carried out in anhydrous methanol; in this case, the
amount of the product in the reaction mixture stopped to
increase from a certain moment, only consumption of the
starting bromide 2b and increase in the amount benzeneꢀ
hexacarboxylate 3 and HMCH were observed. Our atꢀ
tempts to neutralize the forming HBr with bases, for exꢀ
ample, K2CO3 or tertiary amines, were also unsuccessful.
The side reactions considerably dominated when ethanol
or propanol were used, in this case only benzenehexaꢀ
carboxylate 3 and HMCH were mainly detected in the
reaction mixture even for the low conversions of the startꢀ
ing bromide 2b.
All the synthesized halocycloheptatrienes 2a—c are
colorless compounds, which distinguishes them from the
penta(methoxycarbonyl)cyclopentadiene halides, which in
solution have electron absorption spectra identical to the
spectrum of penta(methoxycarbonyl)cyclopentadienyl
anion. The absence in 2a—c of strong crimson color charꢀ
acteristic of anion 1 and their specific behavior in the
reactions with nucleophiles indicate that these compounds
are prone to a heterolytic cleavage of the C—Hal bond
with elimination of the halide anion and an instantaneous
transformation of the formed unstable hepta(methoxyꢀ
carbonyl)tropylium.
7ꢀChloroꢀ1,2,3,4,5,6,7ꢀhepta(methoxycarbonyl)cycloheptaꢀ
1,3,5ꢀtriene (2a). Chlorine gas was passed through a solution of
compound K[1] (0.54 g, 1 mmol) in acetonitrile (10 mL) until
a crimson color disappeared. The solvent was evaporated in vacuo,
the residue was treated with AcOEt (5 mL) and the mixture was
passed through a layer of silica gel (about 1 cm), which was
additionally washed with AcOEt (3 mL). After evaporation of
the solvent, 2a (0.52 g, 98%) was obtained as colorless crystals,
m.p. 170—171 C (decomp.). Found (%): C, 47.22; H, 4.00.
C21H21ClO14. Calculated (%): C, 47.34; H, 3.97. MS (EI), m/z
(Irel (%)): 501 (15), 503 (6) [M – OMe]+; 473 (98), 475 (48)
[M – CO2Me]+; 453 (65); 395 (48); 59 (100) [CO2Me]+. 1H NMR
(CDCl3, 50 C), : 3.75 (s, 3 H, OMe); 3.77, 3.81, 3.86 (all s,
6 H each, 6 OMe). 13C NMR (CDCl3, 50 C), : 53.0 (2 OMe);
53.2 (4 OMe); 54.7 (OMe); 66.7 (br, C(7)); 127.8 (br, =C);
136.0 (=C); 145.4 (br, =C); 162.9, 163.5, 164.4 (6 COO); 165.0
(COO). 1H NMR (CDCl3, –30 C), : major conformer: 3.65
(s, 3 H, OMe); 3.68, 3.75, 3.84 (all s, 6 H each, 6 OMe); minor
conformer: 3.71, 3.73, 3.76 (all s, 6 H each, 6 OMe); 3.77
(s, 3 H, OMe). 13C NMR (CDCl3, –30 C), : major conformer:
53.4 (2 OMe); 53.7 (4 OMe); 55.2 (OMe); 66.6 (br, C(7)); 126.3
(=C); 135.5 (br, =C); 144.4 (=C); 163.0, 163.5, 164.2 (6 COO);
165.5 (COO); minor conformer: 51.8, 53.7, 53.8 (6 OMe); 54.7
(OMe); 66.6 (C(7)); 132.4 (=C); 135.5 (br, =C); 136.4 (=C);
163.7, 164.2, 164.6 (6 COO); 166.3 (COO).
7ꢀBromoꢀ1,2,3,4,5,6,7ꢀhepta(methoxycarbonyl)cycloheptaꢀ
1,3,5ꢀtriene (2b). A solution of bromine (0.16 g, 1 mmol) in
acetonitrile (1 mL) was added to a solution of K[1] (0.54 g,
1 mmol) in acetonitrile (10 mL) and the mixture was stirred for
10 min at 20 C. The solvent was evaporated in vacuo, the resiꢀ
due was treated with AcOEt (5 mL), and the mixture was passed
through a short layer of silica gel, which was additionally washed
with AcOEt (3 mL). After evaporation of the solvent, bromide 2b
(0.57 g, 98%) was obtained as yellowish crystals, m.p. 162—164 C
(decomp.). Found (%): C, 43.50; H, 3.61. C21H21BrO14. Calcuꢀ
lated (%): C, 43.69; H, 3.67. MS (EI), m/z (Irel (%)): 545 (3),
547 (3) [M – OMe]+; 517 (28), 519 (29) [M – CO2Me]+; 497
(32); 453 (68); 395 (93); 59 (100) [CO2Me]+. 1H NMR (CDCl3,
50 C), : 3.67 (s, 3 H, OMe); 3.70, 3.74, 3.78 (all s, 6 H each,
6 OMe). 13C NMR (CDCl3, 50 C), : 52.0 (br, C(7)); 53.0
(2 OMe); 53.2 (4 OMe); 54.6 (OMe); 128.1 (br, =C); 136.3 (=C);
143.5 (br, =C); 163.5 (4 COO); 164.4 (2 COO); 165.8 (COO).
1H NMR (CDCl3, –30 C), : major conformer: 3.75 (s, 3 H,
OMe); 3.79, 3.85, 3.95 (all s, 6 H each, 6 OMe); minor conꢀ
former: 3.82, 3.84, 3.87 (all s, 6 H each, 6 OMe); 3.89 (s, 3 H,
OMe). 13C NMR (CDCl3, –30 C), : major conformer: 51.0
(br, C(7)); 53.3 (2 OMe); 53.6 (4 OMe); 55.1 (OMe); 126.4
(=C); 135.6 (br, =C); 144.3 (=C); 163.1, 163.5, 164.2 (6 COO);
165.5 (COO); minor conformer: 51.0 (C(7)); 51.9 (2 OMe); 53.7
(4 OMe); 54.7 (OMe); 132.5 (=C); 135.6 (br, =C); 136.5 (=C);
163.7 (4 COO); 164.6 (2 COO); 166.2 (COO).
Experimental
1
H and 13C NMR spectra were recorded on Bruker AMX
400 (400.1 and 100.6 MHz) and Bruker AVANCE II 300 spectroꢀ
meters (300 and 75.5 MHz) for solutions in CDCl3 or (CD3)2SO
containing 0.05% of Me4Si as an internal standard. Mass spectra
were recorded on a Finnigan MAT INCOSꢀ50 instrument
(EI, 70 eV, direct injection); high resolution mass spectra
(ESIꢀHRMS) were obtained on a Bruker micrOTOF II instruꢀ
ment. Thinꢀlayer chromatography was performed on Silicagel
60 plates (Merck). Single crystal Xꢀray diffraction studies of comꢀ
pounds 2a and 2b were carried out on a Bruker 1K SMART
CCD automated diffractometer (MꢀK radiation) at 100 K.
Crystals of both compounds are monoclinic, space group Р21/c.

Halohepta(methoxycarbonyl)cycloheptatrienes
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 1, January, 2015
245
7ꢀFluoroꢀ1,2,3,4,5,6,7ꢀhepta(methoxycarbonyl)cycloheptaꢀ
1,3,5ꢀtriene (2c). Silver fluoride (0.15 g, 1.2 mmol) was added to
a solution of bromide 2b (0.58 g, 1 mmol) in acetonitrile (30 mL).
The mixture was stirred for 4 h, the solvent was evaporated
in vacuo. The residue was treated with chloroform (10 mL) and
the mixture was passed through a short layer of silica gel, which
was additionally washed with CHCl3 (3 mL). After evaporation
of the solvent, fluoride 2c (0.50 g, 97%) was obtained as a waxꢀ
like mass. MS (EI), m/z (Irel (%)): 485 (12) [M – OMe]+; 457
(100) [M – CO2Me]+; 429 (32); 395 (30); 355 (28); 59 (55)
remove HMCH left after chromatography. After evaporation of
ether, compound 5 (0.14 g, 52%) was obtained as a yellow oil.
HRMS (ESI): found: m/z 551.1009; C22H24O15; calculated:
551.1007 [M+Na]+. 1H NMR (CDCl3, 25 C), : 3.31 (br.s, 3 H,
OMe); 3.75 (br.s, 18 H, 6 OMe); 3.84 (br.s, 3 H, OMe).
13C NMR (CDCl3, 25 C), : 53.4, 53.5, 53.7 (6 OMe); 54.2
(CO2Me at C(7)); 56.7 (OMe); 81.4 (br, C(7)); 128.2 (br, =C);
132.2 (C=); 134.0 (br, =C); 164.3, 165.0, 165.1 ((6 COO); 167.3
(COO at C(7)).
[CO2Me]+. HRMS (ESI): found: m/z 539.0817; C21H21FO14
;
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 12ꢀ03ꢀ00703).
calculated: 539.0808 [M+Na]. 1H NMR (CDCl3, 27 C), : 3.75
(s, 3 H, OMe); 3.76, 3.79, 3.86 (all s, 6 H each, 6 OMe).
13C NMR (CDCl3, 27 C), : 53.4 (6 OMe); 54.6 (OMe); 90.8
(br.d, C(7), 1JC,F = 192 Hz); 126.6 (br, =C); 136.0 (=C); 142.4
(br, =C); 161.8, 163.2, 164.3 (6 COO); 163.3 (br, COO).
19F NMR (CDCl3), : –165.4.
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7ꢀAzidoꢀ1,2,3,4,5,6,7ꢀhepta(methoxycarbonyl)cycloheptaꢀ
1,3,5ꢀtriene (4). A solution of bromide 2b (0.10 g, 0.17 mmol)
and sodium azide (0.017 g, 0.26 mmol) in MeOH (5 mL) was
stirred for 3 h at 20 C. A precipitate formed was filtered off and
dried in vacuo at 0 C to obtain azide 4 (0.052 g, 60%) as colorless
crystals, slowly decomposing at room temperature, that is charꢀ
acterized by the appearance and a gradual increase in the conꢀ
tent of benzenehexacarboxylate 3. HRMS (ESI): found: m/z
562.0923; C21H21N3O14; calculated: 562.0916 [M+Na]+. IR
(KBr), /cm–1: 2130, 1738. 1H NMR (DMSOꢀd6), : 3.74, 3.76
(both s, 9 H and 12 H, 7 OMe). 13C NMR (DMSOꢀd6), : 53.2
(6 OMe); 54.2 (OMe); 73.6 (C(7)); 130.5, 135.5, 139.5 (all br,
=C); 161.5, 162.8, 163.3 (6 COO); 165.3 (br, COO). 14N NMR
(DMSOꢀd6), : –138.2 (br.s).
7ꢀMethoxyꢀ1,2,3,4,5,6,7ꢀhepta(methoxycarbonyl)cycloheptaꢀ
1,3,5ꢀtriene (5). A solution of bromide 2b (0.29 g, 0.5 mmol) in
methanol (20 mL) was refluxed under argon for 20 h. The solꢀ
vent was evaporated in vacuo and the residue was subjected to
chromatography on a column with SiO2 (eluent CHCl3—AcOEt,
4 : 1). The fraction containing compound 5 was dissolved in
diethyl ether and washed with 50% aqueous solution of NaOH to
Received September 2, 2014