Adamantylazoles: IV acid-catalyzed adamantylation of pyrazoles

Article abstract of DOI:10.1023/A:1013930219704

Pyrazoles with pK_BH⁺ no more than 0.8 and having substituents in 3(5) position with effective van der Waals radii not exceeding 2 A in a mixture of phosphoric and acetic acids at weight ratio 4 : 1 (H₀ -1,8) react with 1-adamantanol to afford the corresponding 1-(1-adamantyl)-or 1,4-di(1-adamantyl)pyrazoles.

Full text of DOI:10.1023/A:1013930219704

Russian Journal of Organic Chemistry, Vol. 37, No. 12, 2001, pp. 1741 1746. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 12, 2001,
pp. 1822 1827.
Original Russian Text Copyright
2001 by Gavrilov, Golod, Kachala, Ugrak.
Adamantylazoles: IV* Acid-Catalyzed Adamantylation
of Pyrazoles
A. S. Gavrilov, E. L. Golod, V. V. Kachala, and B. I. Ugrak
St. Peresburg State Technological Institute, St. Petersburg, 198013 Russia
Received May 3, 2000
+
Abstract Pyrazoles with pKBH no more than 0.8 and having substituents in 3(5) position with effective van
der Waals radii not exceeding 2 in a mixture of phosphoric and acetic acids at weight ratio 4: 1 (H0 1,8)
react with 1-adamantanol to afford the corresponding 1-(1-adamantyl)- or 1,4-di(1-adamantyl)pyrazoles.
N-Adamantylation of azoles (including pyrazoles)
described in the literature occurred in reactions with
1-bromoadamantane either in a high-pressure reactor
at 180 200 C or at heating in a microwave oven
[2 4]. Adamantylation of azoles may be performed
as an acid-catalyzed reaction [1, 5, 6]. The target of
this study was investigation of 1-adamantanol (I)
reaction with pyrazoles in acidic media. It was shown
previously by the imidazole example that adamantyl-
ation in the acidic medium depended first of all on
protolytic equilibria. It was presumable that this rule
would be valid also for pyrazoles. However in selec-
tion of substrates for the study of adamantylation we
met with a limited number of data on basicity con-
stants of pyrazoles, especially those with electron-
withdrawing substituents [7]. The published relation
The calculations were carried out with the use of
Statgraphics Plus software. The preliminary calcula-
tions showed that parameter E did not affect the final
correlation form, and thus it was excluded from the
final computation.
The analysis proceeding from the data for 35
compounds containing electron-withdrawing substitu-
ents in C3 5 positions and electron-donating ones and
phenyl in C3,4 positions resulted in the following
equation:
+
pKBH
=
(9.20 0.16)
(7.01 0.40)
I(3) c(3)
(5.84 0.12)
(4.34 0.24) c(4)
(1)
I(4)
(7.22 0.53)c(5) + (2.24 0.06)
R = 0.9945, S = 0.16.
+
between pKa and pKBH is based on few points and
provides the values for 3-nitro- and 3,4-dinitropyr-
azoles with large errors. Besides no published data
exist on the basicity and acidity of pyrazolecarboxylic
acids. Therefore we tried to fill in this gap using the
correlation analysis procedure previously successfully
applied to evaluation of basicity for 1,2,4-triazoles
The computation results are presented in Table 1.
The basicity constants for pyrazoles that were absent
in the literature in this study were calculated by
equation (1). The first object of the study was 3-carb-
+
oxy-4-nitropyrazole (IIa) (pKBH
4.8) that in 85%
sulfuric acid at 22 C in 72 h yielded 1-(1-adamantyl)-
3-carboxy-4-nitropyrazole (IIIa).
[8]. We performed a six-parametric correlation of
+
pyrazoles pKBH values with the constants
and
I
c
of substituents at C3, C4, C5. The basicity values
were taken from review [7], and from [9]. The
I
c
general form of the correlation equation is as follows:
+
pKBH = A I(3) + B c(3) + C I(4) + D
c(4)
Under the same conditions 5-methyl-3,4-dinitro-
pyrazole (IIb) (pKBH 8.1) reacted similarly afford-
+ E I(5)+ F c(5)+ G,
+
ing
1-(1-adamantyl)-5-methyl-3,4-dinitropyrazole
where the figures in the parentheses are the numbers
of the corresponding carbon atoms of the ring.
(IIIb). Pyrazoles of higher basicity do not react under
these conditions. We believed that this fact was due
to high degree of heterocycle protonation and tried to
*
For communication III see [1].
1070-4280/01/3712-1741$25.00 2001 MAIK Nauka/Interperiodica

1742
GAVRILOV et al.
Table 1. Experimental and calculated basicity values
pKBH of pyrazoles
3-methyl-4-nitropyrazole (IIId). These data show that
+
sulfuric acid is suitable for pyrazoles adamantylation
+
at pKBH of substrates below 2.0.
Substituents
Calculated by Experimental [7]
equation (1)
Further we performed pyrazoles adamantylation
in a system phosphoric acid acetic acid, 4: 1 (by
weight), that had been used before in nitroimidazoles
adamantylation [1]. First of all we determined the
acidity function H0 of the said system. As indicator
was used 4-nitropyrazole (IId). The protonation
degree of the indicator was measured by the chemical
shift of CH-protons in the 1H NMR spectrum. The Ho
value found for the system H3PO4 AcOH 4: 1 (by
weight) was 1.8.
3-Me
3-t-Bu
4-Me
3-Et
3,4-Me2
3,5-Me2
3,4,5-Me3
3-Ph
4-Ph
3-Ph-4-Me
3-Ph-5-Me
5,4-Me2-3-Ph
4-NO2
4-NO2-3,5-
4-NO2-3-Me
4-Cl
4-Br
3-NO2
3-Cl
3.08
3.52
2.76
3.27
3.60
3.92
4.44
2.09
2.13
2.61
2.93
3.45
2.09
0.41
1.25
0.54
0.57
4.60
0.40
0.43
0.48
2.03
1.20
1.39
1.40
0.39
2.24
1.59
2.21
0.42
4.44
4.62
1.25
2.24
1.56
3.27
3.25
3.04
3.25
3.85
4.06
4.56
2.09
1.64
2.64
2.87
3.42
2
0.45
1.23
0.59
0.63
4.66
0.49
0.29
0.44
1.86
0.95
1.4
1.43
0.25
2.26
1.5
2.18
0.29
4.53
4.44
1.18
2.47
1.48
The reaction in the system H3PO4 AcOH was
carried out at 60 C. It turned out that within 3 h
cleanly reacted compound IId and 4-bromo-3-carb-
+
oxypyrazole (IIe) (pKBH
2.2). The reaction of
pyrazoles of higher basicity, 3,5-dimethyl-4-nitropyr-
+
azole (IIf) (pKBH 0.45 [7]), and especially 4-chloro-
+
pyrazole (IIg) (pKBH 0.59 [7]) took more time, 4
8 h. In all cases were obtained the corresponding
N1-adamantylpyrazoles.
3-Cl-5-Me
3-Br-5-Me
3,4-Br2
3,4-Br2-5-Me
3-Me-4-Cl
3-Me-4-Br
3-Ph-4-Cl
3,5-Me2-4-Br
3-Et-4-Br
3,5-Me2-4-Cl
3-Ph-4-Br
3,4-Me2-5-Et
3,5-Et2-4-Me
5-Me-3-Ph-4-Br
3,4,5-H
R3 = COOH, R4 = NO2, R5 = H (a); R3 = R4 =
NO2, R5 = Me(b); R3 = R5 = H, R4 = NO2 (c);
R3 = Me, R4 = NO2, R5 = H (d); R3 = COOH,
R4 = Br, R5 = H (e); R3 = R5 = Me, R4 = NO2
(f); R4 = Cl, R3 = R5 = H (g).
+
3,5-Dimethylpyrazole (pKBH 4.06 [7]) did not
react with 1-adamantanol. The data obtained confirm
the assumption that adamantylation occurs only with
nonionized pyrazole.
4-Cl-3-Et
The adamantylation of pyrazoles with unoccupied
C4 position is accompanied with formation of
use in the reaction less concentrated sulfuric acid. It
was shown by an example of 3-nitro-1,2,4-triazole
that adamantylation proceeded at sulfuric acid con-
centration higher than 70% [5]. In order to find out
whether pyrazoles adamantylation in sulfuric acid is
promising we carried out the reaction with 72%
H2SO4 (HO 6.2). It turned out however that in such
acid within 7 days at 18 20 C considerably (but not
+
completely) reacted 4-nitropyrazole (IIc) (pKBH
2.0 [7]), and 3-methyl-4-nitropyrazole (IId) (pKBH
+
1.23[7]) gave rise only to traces of 1-(1-adamantyl)-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 12 2001

ADAMANTYLAZOLES: IV
4-adamantyl derivatives. Thus from 3-nitro-5-methyl-
1743
3-nitro-1,2,4-triazole in the system phosphoric acid
acetic acid arises 1-adamantyl-3-nitro-1,2,4-triazole.
Since N-adamantylation in contrast to C-adamantyla-
tion is reversible, on long keeping (60 days at 20 C)
compound IIIh nearly completely is converted into
a mixture of pyrazoles IVh and Vh. In 96% H2SO4
at 20 C compound IVh is completely transformed
into Vh: Heterolysis of the N Ad bond is an easy
process, and protonation at the nitrogen atom
prevents N-adamantylation of the ring.
+
pyrazole (IIh) (pKBH
3.77) we obtained
1-(1-adamantyl-5-methyl-3-nitropyrazole (IIIh),
1,4-di(1-adamantyl)-5-methyl-3-nitropyrazole (IVh),
and 4-(1-adamantyl)-5-methyl-3-nitropyrazole (Vh).
It is presumable that first arises compound IIIh
which under the reaction conditions is converted into
1,4-diadamantyl derivative. The latter in its turn
suffers heterolysis of the N Ad bond to afford 4-(1-
adamantyl)-5-methyl-3-nitropyrazole (Vh). In general
the processes occurring in adamantylation of com-
pound IIh may be described by the following scheme.
The adamantylation is characterized by regio-
selectivity caused by steric factor: The adamantyl
group does not enter into N1 position when in the
neighboring C5 position are present substituents with
van der Waals radii exceeding 2 (NO2, COOH).
+
3,5-Dicarboxypyrazole (pKBH
0.85) and
+
4-bromo-3,5-dicarboxypyrazole (pKBH 2.52), do not
react at all. As follows from the quantum-chemical
calculations by AM1 method the carboxy groups of
these compounds lie virtually in the plane of the ring
and hamper the attack of the 1-adamantyl carbocation
on the N1-position. A similar situation is observed in
compound IIh: the angle between the planes of the
ring and the nitro group is 5.2 . However at the
attack of the 1-adamantyl carbocation on the C4-
position the nitro group rotates relative to the ring by
sufficiently large angle permitting the addition of the
adamantyl group to the pyrazole ring.
Similarly adamantylation of 3-nitro- (IIi) and
+
+
3-carboxypyrazole (IIj) (pKBH
4.66 [7], pKBH
0.50 respectively) gives rise to N1-monoadamantyl
and 1,4-diadamantyl derivatives; however no traces
were detected of 4-adamantylpyrazoles.
The structure of compounds obtained was proved
1
1
by H and 13C NMR spectra. In the H NMR spectra
appear the signals of monosubstituted adamantyl, of
methyl and carboxy groups, and of the protons of pyr-
azole ring. The 13C NMR spectral parameters (13C
chemical shifts and direct and long-range coupling
constants of 13C and protons) provide more important
information on the structure of adamantylazoles.
R3
= NO2 (i), COOH (j).
Similar transformations were formerly observed at
heating 1- and 4-adamantyl-3,5-dimethylpyrazoles
with hydrochloric acid at 190 200 C [2]. The
adamantylation into 4 position does not result from
intramolecular rearrangement: 1,5-Dimethyl-3-nitro-
pyrazole (IIk) under the above conditions readily
The position of a nitro group in the pyrazole ring
both when it is a single substituent or there are the
other substituents on carbon atoms can be derived
from the chemical shifts of the ring carbons and from
the direct and long-range coupling constants of 13C
and protons. It was formerly established that in
3,5-disubstituted pyrazoles with nitro group at C3
atom the difference of the chemical shifts C3 C5
amounts from 7 to 24 ppm, and at the nitro group in
C5 position this difference is from 16 to + 6 ppm
due to dissimilar electronegativity of atoms N1 and
N2 in the pyrazole ring [10]. The coupling constants
yields 4-(1-adamantyl)-1,5-dimethyl-3-nitropyrazole
(IIIk).
Compound Vl forms through the rupture of N Ad
bond to give 1-adamantyl carbocation. This statement
is supported by the fact that on prolonged keeping of
a mixture containing adamantylpyrazole IIIh and
1
13C, H also confirm the structure. The vicinal coupl-
13
5
3
ing constants
J
in compounds with a nitro
C ,C
group in C3 position equal from 11 to 15 Hz and the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 12 2001

1744
GAVRILOV et al.
Table 2. 1H NMR spectra of 1-adamantylpyrazoles, , ppm
Compd. no.
Chemical shifts, multiplicity, and integral intensity of proton signals
IIIa
IIIb
IIIca
IIIda
IIIea
IIIf
8.35 s (1H, H5); 4.7 br.s (COOH); 2.98 br.s, 2.19 br.s 1.63 br.s (15H, Ad)
2.8 s (3H, 5-Me); 2.31 br.s, 1.71 br.s (15H, Ad)
8.15 s (1H, H3); 8.0 s (1H, H5); 2.1 br.s, 1.8 br.s (15H, Ad)
8.7 s (1H, H5); 2.5 (3H, 3-Me); 2.1 br.s, 1.75 br.s (15H, Ad)
8.3 s (1H, H5); 2,1 br.s, 1.7 br.s (15H, Ad)
2.81 s (3H, 5-Me); 2.45 s (3H, 3Me); 2.28 br.s, 2.22 br.s, 1.74 br.s (15H, Ad)
IIIga
IIIh
IIIi
7.4 s (2H, H3, H5); 2.1 br.s, 1.7 br.s (15H, Ad)
6.61s (1H, H4), 2.53 s (3H, 5-Me); 2.29 br.s, 2.23 br.s, 1.78 br.s (15H, Ad)
7.43 s (1H, H5); 6.37 s (1H, H4); 2.12 br.s, 2.05 br.s, 1.63 br.s (15H, Ad)
7.53 s (1H, H5); 6.8 s (1H, H4); 2.2 br.s, 1.75 br.s (15H, Ad)
3.75 s (3H, 1-Me); 2.4 s (3H, 5-Me); 2.03 br.s, 1.7 br.s (15H, Ad)
2.26 s (3H, 5-Me); 2.29 br.s, 2.22 br.s, 2.03 br.s, 2.01 br.s, 1.72 br.s (30H, Ad)
7.32 s (1H, H5); 2.26 br.s, 2.18 br.s, 2.06 br.s, 2.03 br.s, 1.77 br.s, (30H, Ad)
7.3 s (1H, H3); 2.13 br.s 2.0 br.s 1.75 br.s (30H, Ad)
IIIja
IIIka
IVh
IVi
IVja
Vh
10.3 br.s ,(1,2,H1); 2.49 s (3H, 5-Me); 2.09 br.s, 2.06 br.s, 1.71 br.s, (15H, Ad)
a
The spectra were registered on spectrometer Perkin-Elmer R-12.
Table 3. 13C NMR spectra of 1-adamantylpyrazoles, C, ppm
Compd.
no.
C3
C4
C5
Ad
C=O, Me
IIIa
1-Ad: 29.40 d, 35.59 t, 42.15 t, 3-COOH
62.56 159.71 s
1-Ad: 30.19 d, 36.01 t, 41.92 t, 5-CH3
IIIb 147.19 br.s
126.66 br.s
140.74 q (6.4)
140.34 q (7.5)
66.96 s
13.78 quint (128.7)
IIIf 144.53 q (6.2) 132.81 br.s
1-Ad: 30.51 d, 36.49 t, 42.37 t, 5-CH3 and-CH3
63.73 s
14.87 quint (128.4)
14.71 quint (130.5.)
IIIh 153.36 br.s
IIIi 155.79 br.s.
IVh 153.56 br.s.
104.46 d.q
(185.0, 6.0)
102.57 d.d.
(186.3, 8.2)
119.7 s
141.228 d.q
(8.0, 8.0)
127.93 d.d.
(190.2, 8.1)
1-Ad: 29.8 d, 35.9 t, 41.9 t, 5-CH3
63.9 s
15.17 quint (130.0)
1-Ad: 29.85 d, 36.18 t, 42.85 t,
61.60 s
136.83 quint (6.2) 1-Ad: 30.31 d, 36.94 t, 42.14 t, 5-CH3
63.58 s 4-Ad: 29.02 d, 34.42 s, 16.26 quint (128.7)
36.37 t, 41.21 t
IVi
Vh
153.06 br.s.d 127.66 d (6.3) 125.15 d (187.7) 1-Ad: 29.86 d, 36.99 t, 42.75 t,
(9.8)
60.99 s 4-Ad: 28.91 d,
33.21 s, 36.23 t, 41.32 t
156.30 br.s
120.71 s
138.48 quint (5.8) 4-Ad: 28.95 d, 34.43 s, 36.87 t, 5-CH3
41.48 t
14.78 quint (129.5)
13
3
5
coupling constants
J
in compounds with a
Among compounds under study are no 5-nitropyr-
azoles. When nitro group was located at C3 atom the
difference in chemical shifts for C3 C5 was as
expected 7 28 ppm (compounds IIIh , Vh, IVh, IIIa,
C ,C
nitro group in C5 position are from 4.3 to 7.4 Hz
[10]. Similar trends in 13C chemical shifts and coupl-
ing constants 13C, 1H were earlier observed for
N-acetonylnitro-1,2,4-triazoles [11] and N (1-
adamantyl)nitro-1,2,4-triazoles [5].
13
3
5
IIIc, IVc), and the coupling constant
J
was
C ,H
10 Hz (compound IIIf). When the position of sub-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 12 2001

ADAMANTYLAZOLES: IV
1745
Table 4. Reaction time, yields, melting points, and elemental analyses of compounds obtained
Compd. no.
Reaction time, h
Yield, %
mp, C (solvent)
IIIa
IIIb
IIIc
IIId
IIIe
IIIf
IIIg
IIIh
IIIi
IIIj
IIIk
IVh
IVi
3
8
2.5
2.5
3
4
8
3
3
4
3
3
3
4
3
82
32
84
80
70
60
47
23
40
21
60
23
21
7
166 167 (ethanol water 4: 1)
145 147 (ethanol)
155 157 (ethanol)
151 152 (ethanol)
238 239 (ethyl acetate)
174 176 (ethanol)
96 98 (ethanol)
159 160 (ethanol)
124 126 (ethanol)
188 190 (ethanol water 1:1)
96 (ethanol)
250 251 (acetone-chloroform 9:1)
208 210 (ethanol)
229 231 (ethanol water 1:1)
219 220 (ethanol water 4:1)
IVj
Vh
9
Found, %
Calculated, %
Compd.
no.
Formula
C
H
N
C
H
N
IIIa
IIIb
IIIc
IIId
IIIe
IIIf
IIIg
IIIh
IIIi
IIIj
IIIk
IVh
IVi
57.35
65.53
65.16
64.58
51.44
65.16
65.59
64.81
64.01
67.93
65.09
73.07
72.03
75.34
64.86
5.63
7.27
7.57
7.01
5.08
7.57
7.49
7.55
6.82
7.67
7.58
7.99
7.79
8.05
6.73
14.29
12.92
14.96
16.04
8.34
14.96
11.55
16.35
16.04
11.07
15.51
10.63
10.74
7.05
C14H17N3O4
C14H18N4O4
C13H17N3O2
C14H19N3O2
C14H17BrN2O2
C15H21N3O2
C13H17N2Cl
C14H19N3O2
C13H17N3O2
C14H18N2O2
C15H21N3O2
C24H33N3O2
C23H31N3O2
C24H32N2O2
C14H19N3O2
57.70
68.15
65.43
64.34
51.70
65.43
65.95
64.34
63.14
68.27
65.43
72.88
72.41
75.75
64.34
5.88
8.24
7.68
7.32
5.27
7.68
7.24
7.32
6.93
7.36
7.69
8.41
8.19
8.47
7.32
14.43
12.27
15.26
16.07
8.61
15.26
11.83
16.07
16.99
11.37
15.26
10.62
11.01
7.36
IVj
Vh
15.76
16.07
stituent in the ring was not unambiguously derived
from the 13C chemical shifts, we measured spectra
with nuclear Overhauser effect (1D-NOE and
ROESY) [12, 132] that confirmed the presence of
adjacent methyl and adamantyl groups (IIIh, b, f)
and of closely located protons of the ring and
adamantyl group (IIIa, i, IVi) definitely indicating
the presence of a methyl group in C5-position
(IIIh, b, d) or the lack of a substituent in this posi-
tion (IIIa, i, IVi).
The position of the adamantyl moiety is also
indicated by the signal of its quaternary carbon: when
the adamantyl is attached to the N1-position the cor-
responding chemical shifts are equal to 60 64 ppm
(compounds IIIh, IVh, IIIa, b, i, IVi), and when it
is in C4-position the chemical shift is 33 55 ppm
(compounds Vh, IVh, i).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 12 2001

1746
GAVRILOV et al.
Preparation of 4-(1-adamantyl)-5-methyl-3-
The signals of protons attached to the definite
nitropyrazole (Vh). In 25 ml of 96% H2SO4 was dis-
solved 0.01 mol of compound IVh. The mixture was
left standing at 20 C for 24 h, then it was poured into
150 ml of water, and the separated precipitate of
compound Vh was filtered off and washed with
water. Yield 96%.
carbons in the ring were assigned by means of two-
dimensional H/C correlation registered in HMQC
mode (compound IIIc).
EXPERIMENTAL
1H NMR spectra were registered on spectrometer
Perkin-Elmer R-12 (60 MHz), internal reference
Separation of adamantylation products of
3-nitropyrazole (IIi) and 3-carboxypyrazole (IIj).
The precipitate was dissolved in 20 ml of a mixture
ethanol water, 4:1 by volume, or ethanol water 2: 1
by volume respectively, and compounds IVi and IVj
were filtered off; compounds IIIi and IIIj were
isolated by crystallization from the mother liquor.
1
HMDS. Also H and 13C NMR spectra were recorded
on spectrometer Bruker DXR-500 at operating frequ-
encies 500.13 and 125.77 MHz respectively from
1
solutions in CDCl3 of concentration 3 5 mol l at
30 C. All the spectra were recorded on Bruker
DXR-500 instrument in the Fourier-transform mode.
The 13C NMR spectra were registered with wide-band
and selective decoupling from protons. As internal
reference were taken the signals of solvent, deutero-
chloroform: residual protons with chemical shift
7.27 ppm, 77.5 ppm in the 13C spectra. Two-dimen-
sional spectra were obtained along standard proce-
dures ROESY [10] and HMQR [11]. TLC analyses
were performed on Silufol UV-254 plates, develop-
ment under UV-irradiation and in iodine vapor. The
elemental analyses were carried out on CHN-analyzer
Hewlett-Packard 185 B.
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Geterotsikl. Soed., 1996, no. 8, pp. 1078 1087.
6. Saraev, V.V. and Golod, E.L., Zh. Org. Khim.,
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9. Zhdanov, Yu.A. and Minkin, V.I., Korrelyatsionnyi
analiz v organicheskoi khimii (Correlation Analysis
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Pyrazoles adamantylation in sulfuric acid. To
25 ml of 85% sulfuric acid was added 0.01 mol of
1-adamantanol and 0.01 mol of compounds IIa, b.
The mixture was left standing for 3 days at 20 C,
then was poured into 150 ml of water, the separated
precipitate was filtered off and washed with water.
Yield of compound IIIa 60%, of compound IIIb
25%.
Procedure for the synthesis of N-adamantylpyr-
azoles in a mixture H3PO4 AcOH. To 25 ml of a
mixture containing phosphoric and acetic acids in a
weight ratio 4: 1 was added at stirring pyrazole IIa k
(0.01 mol) and 1-adamantanol (I) (0.01 mol). The
mixture was heated to 60 C for 2 8 h (see Table 4),
then poured into 150 ml of water, the separated
precipitate was filtered off and washed with water.
Separation of the products from 3-nitro-5-
methylpyrazole adamantylation. The precipitate was
dissolved in 30 ml of a mixture ethanol water, 4: 1,
and the insoluble part (compound IVh) was separated.
From the mother liquor compound IIIh was isolated
by crystallization. The mother liquor was evaporated
to 10 15 ml, and compound Vh was then isolated.
11. Semenov, V.V., Ugrak, B.I., and Shevelev, S.A.,
Izv. Akad. Nauk SSSR, Ser. Khim., 1990, no. 8,
pp. 1827 1837
12. Bakh, A. and Davis D.G., J.Magn. Reson., 1985,
vol. 63, no. 2, pp. 207 213.
13. Bakh, A., Griffety, R.H., and Hawkins, B.L.,
J. Magn. Reson., 1983, vol. 55, no. 2, pp. 301 315.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 12 2001