Synthesis of some [1,2,4]triazino[5,6-b]quinoline derivatives [1]

Article abstract of DOI:10.1002/jhet.5570390630

By coupling of diazonium salts with ethyl N-(4-oxo-1,4-dihydroquinolin-2-yl)carbamate 4, the corresponding 3-arylazocompounds 5 were obtained. These ones were cyclized thermally or in alkaline medium to the corresponding 2-aryl-2,3,5,10-tetrahydro-[1,2,4]triazino[5,6-b]quinolin-3,10-diones 6. Compounds 6 were transformed by alkaline hydrolytic splitting to the corresponding 2-amino-3-arylazo-1,4-dihydroquinolin-4-ones 7. Starting carbamate 4 was prepared by a two-step synthesis from 2-amino-1,4-dihydroquinolin-4-one 1.

Full text of DOI:10.1002/jhet.5570390630

Nov-Dec 2002
Synthesis of Some [1,2,4]Triazino[5,6-b]quinoline Derivatives [1]
1305
1
2
1
Jakub Sty´skala* , Antonín Lycˇka and Jan Slouka
1
Department of Organic Chemistry, Palacky´ University, 771 46 Olomouc, Czech Republic
E-mail: styskala@prfnw.upol.cz
Research Institute for Organic Syntheses, 532 18 Pardubice – Rybitví, Czech Republic
2
E-mail: antonin.lycka@vuosas.cz
By coupling of diazonium salts with ethyl N-(4-oxo-1,4-dihydroquinolin-2-yl)carbamate 4, the corre-
sponding 3-arylazocompounds 5 were obtained. These ones were cyclized thermally or in alkaline medium
to the corresponding 2-aryl-2,3,5,10-tetrahydro-[1,2,4]triazino[5,6-b]quinolin-3,10-diones 6. Compounds 6
were transformed by alkaline hydrolytic splitting to the corresponding 2-amino-3-arylazo-1,4-dihydroquino-
lin-4-ones 7. Starting carbamate 4 was prepared by a two-step synthesis from 2-amino-1,4-dihydroquinolin-
4-one 1.
J. Heterocyclic Chem., 39, 1305(2002).
The syntheses of condensed [1,2,4]triazines based on the
spectroscopy is capable of distinguishing these forms
15
cyclization of hydrazono-carbamates are advantageous in
the cases when the starting compounds can be obtained by
azo-coupling reactions with five membered aromatic hete-
rocyclic compounds, e.g. at the synthesis of the pyra-
zolo[3,4-e][1,2,4]triazines [2], [1,2,4]triazinoindoles [3,4]
or [1,2,4]triazines with condensed furan [5,6] or thiophene
ring [7].
We were interested in the extension of the method men-
tioned above to be usable for a synthesis of [1,2,4]triazines
with fused six membered heterocyclic ring. It is known
that the reactivity of these compounds to nucleophilic
attacks is much lower then that of aromatic heterocyclic
compounds with a five membered ring.
undoubtedly. There were two signals in N NMR spec-
15
trum of structure 3 [d( N) = -126.2 and –263.0]). The
nitrogen signal resonating at –126.2 ppm had a very simi-
15
lar N chemical shift to that one in 2-aminopyridine
15
[d( N) = -113.8, [14]]. The nitrogen signal resonating at
–263.0 ppm belonged to the NH group. These values indi-
cate clearly that the structure 2 was not the correct struc-
15
ture because the d( N) were considerably different from
those in the model compounds related to structure 2, i.e. in
1,4-dihydropyridine-4-one and 1-methyl-1,4-dihydropyri-
15
dine-4-one, the N chemical shift were –222 ppm and
–248 ppm, respectively [12].
We found that the ethoxycarbonyl group placed in posi-
tion 4 of compound 3 caused a lack of reactivity for cou-
pling reactions, and could be easily hydrolysed contrary to
In this paper, we describe an application of this method
to a quinoline system in order to investigate an alternative
route for the synthesis of the little explored [1,2,4]tri-
azino[5,6-b]quinoline system [8,9].
Scheme 1
As a starting material, we chose a compound which is
stated in references as 2-amino-4-hydroxyquinoline
15
[10,11,12]. On the basis of N NMR spectroscopy we
found that this compound exists as 4-oxo-1,4-dihydro-
15
quinoline tautomer 1. Two resonances in N NMR spec-
15
trum of this compound [d( N) = -261.6 (NH, broadened
I
15
1
signal) and –310.7 (NH , J( N, H) = 88.8 Hz] give the
2
evidence that the structure 1 is strongly over dominating
15
form (compared to d( N) = - 248 in 1-methyl-1,4-dihy-
15
dropyridine-2-one [13], and to the N chemical shift of
substituted amino group at cca. 50 ppm [14]).
Within our effort to prepare ethyl N-(4-oxo-1,4-dihydro-
quinoline-2-yl)carbamate 4 we carried out the acylation of
compound 1 with ethyl chloroformate in pyridine medium.
However, direct monoacylation was unsuccessful. This
fact can be explained by the formation of the tautomeric
equilibrium in pyridine, where 2-amino-4-hydroxyquino-
line is formed and which is more reactive at both reaction
centres than tautomer 1. Thus, the mixture of starting com-
pound 1 and twice acylated derivative 3 was formed
despite the usage of only one mol of ethyl chloroformate.
Compound 3 was prepared later by acylation with the
15
excess of ethyl chloroformate in a good yield. N NMR

1306
J. Sty´skala, A. Lyˇckaand J. Slouka
Vol. 39
the carbamate group placed in position 2. For this reason it
was possible to convert compound 3 to ethyl N-(4-oxo-1,4-
dihydroquinoline-2-yl)carbamate 4 in a good yield by boil-
ing in aqueous ethanol – pyridine mixture.
solutions with the formation of red coloured solutions of
mesomeric anoints. After standing for 24 hours at a room
temperature it was possible to recover them unchanged
from these solutions. However, boiling in basic solution of
sodium hydroxide led to the hydrolytic splitting of
[1,2,4]triazine ring and the formation of the corresponding
2-amino-3-arylhydrazono-3,4-dihydroquinolin-4-ones,
which were tautomeric with the corresponding azo deriva-
tives 7. These compounds were identical to compounds
which had been prepared by coupling reactions of diazo-
nium salts with 2-amino-1,4-dihydroquinolin-4-one 1.
Sample 7 shows extremely low solubility even in hexa-
The determination of the tautomeric form of carbamate
15
4 by N NMR spectroscopy was not successful. No sig-
13
nals were observed. Even in C NMR some signals were
not present and some were very broad since there was
probably a complicated dynamic equilibrium.
Our next interest was focused to azo coupling reactions
of carbamate 4 with diazonium salts to obtain 3-arylazo
derivatives 5. These ones are suitable synthones for
[1,2,4]triazino[5,6-b]quinoline skeleton formation.
15
deuteriodimethyl sulfoxide and, thus, N enrichment had
15
In agreement with our hypothesis, we found that the
reactivity of carbamate 4 was lower than the reactivity of
analogous heterocyclic carbamates with five a membered
ring [2-7]. The best yields of coupling reactions were
reached in pyridine medium where carbamate 4 reacted
with diazotised 4-nitroaniline resulting in 3-(4-niropheny-
lazo)-derivative 5c. Lower yields were obtained with dia-
zotised aniline and 4-bromoaniline resulting in the corre-
sponding derivatives 5a and 5b. The coupling reaction of
carbamate 4 with diazotised 4-methoxyaniline was unsuc-
cessful. The yield improvement of 3-arylazoderivatives
was not successful neither by the mutual change of the
components ratio nor by carrying out the reaction in aque-
ous basic medium. It was possible to increase the yields
only by the isolation of unchanged carbamate 4 after the
coupling reaction and re-using it for next procedure. If the
azo coupling reactions proceed in triethylamine – pyridine
mixture for a long reaction time (Method D), cyclized
compounds 6 were isolated.
to be used in order to determine N chemical shifts. The
15
N selectively labelled compound 7a was prepared using
15
15
15
either N enriched aniline (96 % N) or N enriched
Na NO (50 % N). The two N chemical shifts mea-
15
15
15
2
15
sured in the N selectively labelled compound 7a [45.4
15
15
15
( N enrichment from Na NO ), 115.0 ( N enrichment
2
15
from N-aniline)] indicate that compound 7a exists in
pure azo form [15]. The N NMR signals of other two
15
nitrogens were not observed due to low solubility and thus,
no further conclusions could be made about other possible
tautomeric equilibria.
We have attempted to prepare compound 5 from 7 by
treatment of ethyl chloroformate, but the reaction was
unsuccessful due to the low solubility of the compound 7.
EXPERIMENTAL
The melting points were determined on a Boetius stage and are
uncorrected. The infrared spectra were recorded in KBr wafers
and scanned on an ATI Unicam Genesis FTIR instrument.
Elemental analyses were performed with an EA 1108 Elemental
Analyzer (Fison Instrument). 15N (36.50 MHz), 13C (90.56
15
Two resonances were found in the N NMR spectrum of
15
15
N selectively labelled compound 5a prepared using
N
15
enriched aniline (96 % N compound). The signal at
1
MHz) and H (360.13 MHz) NMR spectra were measured on a
–271.9 ppm belongs to the NHCOOC H group while that
2
5
Bruker AMX 360 spectrometer equipped with 5 mm broadband
probe and a Silicon Graphic Indy computer in hexadeuteriodi-
methyl sulfoxide at ambient temperature. The 13C and 1H chemi-
cal shifts were referred to the central peak of DMSO-D6 (d(13C)
= 39.60, d (1H) = 2.55). The 15N chemical shifts were referred to
external neat nitromethane in a co-axial capillary (d(15N) = 0.0).
Positive values of chemical shifts denote high frequency shifts
with respect to standards.
one at 41.4 ppm can be assigned to N-C H fragment and
6
5
the chemical shift shows that compound 5a exists predomi-
15
nantly in azo form (compared with N chemical shifts in
15
model azo compounds [15]). The difference in N chemical
shifts of N-C H fragment in compounds 7 and 5 is negligi-
6
5
ble and it can be concluded that NHCOOC H group does
2
5
not influence the equilibrium as much as the amino group.
Above mentioned 2-aryl-2,3,5,10-tetrahydro[1,2,4]tri-
azino[5,6-b]quinolin-3,10-diones 6 respectively their
2,3,4,10-tetrahydro tautomers were prepared in high yields
by thermal cyclisation of azo-compounds 5 in boiling
decalin. The lower yield was obtained by basic cyclisation
of compound 5a in hot aqueous ethanolic solution of
sodium hydroxide. Prepared triazino quinolines 6 are yel-
low crystalline substances of high melting points, spar-
ingly soluble in common organic solvents.
2-Amino-1,4-dihydroquinolin-4-one (1) [10,11,12].
1
Compound 1 has H NMR: d 5.56 (s,1H); 6.63 (bs,2H,NH2);
7.21 (d,1H); 7.36 (d,1H); 7.50 (d,1H); 8.08 (d,1H); 11.4
(bs,NH,). 13C NMR: d 90.0; 116.7; 121.8; 124.7; 130.7 (all CH);
123.3; 139.0; 155.1; 175.3 (all C); 15N NMR: d -310.7 (NH2); -
261.6 (NH,bs).
Ethyl N-(4-Ethoxycarbonyloxyquinolin-2-yl)carbamate (3).
To a suspension of 2-amino-1,4-dihydroquinolin-4-one (1)
(9.8 g, 61.2 mmol, dried at 125 °C for 3 hours) in anhydrous pyri-
dine (150 ml), ethyl chloroformate (16 ml, 167 mmol) was added
drop wise through a dropping funnel. The reaction mixture was
[1,2,4]Triazino[5,6-b]quinoline system of compounds 6
is fairy stable. Its derivatives are stable in strongly acidic
medium for 24 hours. Compounds 6 are soluble in basic

Nov-Dec 2002
Synthesis of Some [1,2,4]Triazino[5,6-b]quinoline Derivatives
1307
at 150 °C cyclizes to 6b without melting. IR (cm-1): 3232, 2992,
1729, 1630, 1585, 1544, 1310, 1221, 770.
Anal. Calcd. for C18H15N4O3Br (415.3): C, 52.07; H, 3.64; N,
13.49. Found C, 52.16; H, 3.51; N, 13.32.
allowed to stand overnight at 2-5 °C. Then, it was diluted slowly
with water under stirring to a total volume of 2000 ml. After
standing for 5 hours, the precipitate was collected by filtration,
washed with water and dried. The sample for analysis was pre-
pared by the crystallization from ethanol. The yield 13.8 g (74.0
%), mp 126-128 °C dec. 1H NMR: d 1.30 (t, 3H, CH3); 1.39 (t,
3H, CH3); 4.22 (q, 2H, OCH2); 4.40 (q, 2H, OCH2); 7.57 (t, 1H,
arom.); 7.81 (t, 1H, arom.); 7.86 (d, 1H, arom.); 7.91 (d, 1H,
arom.); 8.16 (s, 1H, arom.); 10.75 (bs, 1H, NH). 13C NMR: d
14.2 and 14.4 (CH3); 61.7 and 65.6 (OCH2); 104.2; 121.2; 125.1;
127.7; 130.6 (all CH); 119.8; 148.0; 151.6; 152.2; 153.2; 155.8
(all C); 15N NMR: d -263.0; (NH, s); -126.2. IR (cm-1): 3151,
2980, 1771, 1736, 1605, 1502, 1371, 1248, 1214, 1081, 767.
Anal. Calcd. for C15H16N2O5 (304.3): C, 59.21; H, 5.30; N,
9.21. Found C, 58.97; H, 5.60; N, 8.91.
Ethyl N-[3-(4-Nitrophenylazo-4-oxo-1,4-dihydroquinolin-2-
yl)carbamate (5c).
A solution of 4-nitroaniline (276 mg, 2.00 mmol) in a mixture
of ice water (12 ml) and 35% hydrochloric acid (2.6 ml) was dia-
zotized with a solution of sodium nitrite (138 mg, 2.00 mmol) in
ice water (6 ml). The mixture was stirred in an ice bath for 15 min
and then added portion wise to a solution of carbamate 4 (464.6
mg, 2.00 mmol) in pyridine (50 ml), which was pre-cooled to 0–5
°C. The mixture was left to stand at 0–5 °C for 48 hours and then
slowly diluted with ice water (60 ml). The next day the precipi-
tated dark orange solid was collected by suction, washed with
water and dried. The sample for analysis was prepared by recrys-
tallization from a large amount of ethanol (0.6 ml per 1 mg).
Yield 330.1 mg (43.3 %), at 210 °C cyclizes to 5c without melt-
ing. IR (cm-1): 3251, 2991, 1721, 1634, 1616, 1586, 1548, 1338,
1211, 753.
Ethyl N-(4-Oxo-1,4-dihydroquinolin-2-yl)carbamate (4).
The product 3 (6.0 g; 19.7 mmol) was dissolved in a mixture of
96% ethanol (75 ml) and pyridine (20 ml). The solution was
refluxed for 10 minutes, decolourised with charcoal and left to
stand at a room temperature. The next day, the crystalline product
was collected by suction, washed with a small amount of ethanol
and dried at 125 °C for 2 hours. The yield 4.58 g (69.2 %); mp
252-254 °C dec. 1H NMR: d 1.31 (t, 3H, CH3); 4.24 (q, 2H,
OCH2); 5.50-6.50 (bs, 1H); 7.34 (t, 1H, arom.); 7.64 (t, 1H,
arom.); 7.70 (d, 1H, arom.); 8.04 (d, 1H, arom.); 10.50 (bs, 1H);
11.40 (bs, 1H). 13C NMR: d 14.4 (CH3); 61.3 (OCH2); 95.6;
123.1; 123.7; 131.0; 153.7. Other signals are very broad: cca
148.0; cca 122.0. IR (cm-1): 3199, 3060, 2979, 1744, 1622, 1583,
1506, 1466, 1245, 1086, 757.
Anal. Calcd. for C18H15N5O5 (381.4): C, 56.69; H, 3.96; N,
18.38. Found C, 56.76; H, 3.79; N, 18.46.
2-Phenyl-2,3,5,10-tetrahydro[1,2,4]triazino[5,6-b]quinolin-3,10-
diones (6a).
Method E.
Compound 5a (17.5 mg, 0.052 mmol) was refluxed in decalin
(3 ml) for 30 min. The mixture was cooled; the precipitated solid
was collected by suction, washed with heptane and dried. The
sample for analysis was prepared by crystallization from acetic
acid (1 ml per 1 mg). Yield 14.1 mg (93.2 %); mp over 360 °C.
1H NMR: d 7.35 (t, 1H, arom.); 7.49 (t, 1H, arom.); 7.55-7.69 (m,
6H, arom.); 7.82 (t, 1H, arom.); 8.12 (d, 1H, arom.); 12.20 (bs,
1H, NH). IR (cm-1): 3063, 1686, 1671, 1621, 1577, 1478, 1235,
802.
Anal. Calcd. for C12H12N2O3 (232.3): C, 62.06; H, 5.21; N,
12.06. Found C, 1.96; H, 5.30; N, 12.01.
Ethyl N-(3-Phenylazo-4-oxo-1,4-dihydroquinolin-2-yl)carba-
mate (5a).
A solution of aniline (186 mg, 2.00 mmol) in a mixture of ice
water (12 ml) and 35% hydrochloric acid (2.6 ml) was diazotized
with a solution of sodium nitrite (138 mg, 2.00 mmol) in ice water
(6 ml). The mixture was stirred in an ice bath for 15 min and then
added portion wise to a solution of carbamate 4 (464.6 mg, 2.00
mmol) in pyridine (50 ml), which was pre-cooled to 0–5 °C. The
mixture was left to stand at 0–5 °C for 48 hours and then evaporated
to dryness. The residue was mixed with water (20 ml) and this mix-
ture was extracted with chloroform (2 x 30 ml). The chloroform
extract was dried with MgSO4, filtered, evaporated to dryness and
dissolved again in chloroform (5 ml). Purification by elution with
chloroform through a short column (4 cm i.d.) filled with silica gel
60 (230-400 mesh, 50 g) gave 120 mg (17,8 %) of orange solid; at
150 °C cyclizes to 6a without melting. The sample for analysis was
prepared by the crystallization from ethanol. 1H NMR: d 1.37 (t,
3H, CH3); 4.35 (q, 2H, OCH2); 7.43-7.86 (m, 8H, arom.); 8.23 (d,
1H, arom.); 11.97 (bs, 1H, NH); 13.50 (bs, 1H, NH). 15N NMR: d
-271.9 (NHCOOC2H5); 41.4 (N-C6H5). IR (cm-1): 3217, 3064,
2981, 1718, 1638, 1604, 1548, 1307, 1227, 764.
Anal. Calcd. for C16H10N4O2 (290.3): C, 66.20; H, 3.47; N,
19.30. Found C, 66.34; H, 3.56; N, 18.89.
Method F.
Compound 5a (20.5 mg, 0.061 mmol) was dissolved in 50 %
aqueous ethanolic solution (5 ml) of NaOH (about 100 mg)
which resulted in a blood red solution. This solution was boiled
for 1-2 min, cooled down and neutralized with diluted acetic
acid. The precipitated yellow solid was collected by filtration,
washed with water and dried to obtain 12.8 mg (72.3 %). Spectral
data were identical to the data of the compound prepared by
method E.
Method D.
A solution of aniline (186 mg, 2.00 mmol) in a mixture of ice
water (8 ml) and 35% hydrochloric acid (1.2 ml) was diazotized
with a solution of sodium nitrite (138 mg, 2.00 mmol) in ice
water (6 ml). The mixture was stirred in an ice bath for 15 min
and then added portion wise to a solution of carbamate 4 (464.6
mg, 2.00 mmol) in pyridine (50 ml) and triethylamine (5 ml),
which was pre-cooled to 0–5 °C. The mixture was left to stand at
0–5 °C for 14 days. Then, the precipitated yellow compound was
collected by filtration, washed with ethanol and dried. Yield
120.0 mg (27.1 %). Spectral data were identical to the data of the
compound prepared by method E.
Anal. Calcd. for C18H16N4O3 (336.4): C, 64.28; H, 4.79; N,
16.66. Found C, 64.21; H, 4.65; N, 16.19.
Ethyl N-[3-(4-Bromophenylazo-4-oxo-1,4-dihydroquinolin-2-
yl)carbamate (5b).
This compound was prepared in a similar way as 5a using
4-bromoaniline (344 mg, 2.00 mmol). Yield 192.1 mg (20.4 %),

1308
J. Sty´skala, A. Lyˇckaand J. Slouka
Vol. 39
2-(4-Bromophenyl)-2,3,5,10-tetrahydro[1,2,4]triazino[5,6-b]-
quinolin-3,10-diones (6b).
2-Amino-3-(4-bromophenylazo)-1,4-dihydroquinolin-4-one
(7b).
This compound was prepared in a similar way as compound 6a
by method A using 5b (108.2 mg) and decalin (4 ml). Yield 94.1
mg (97.8 %), mp over 360 °C. IR (cm-1): 1686, 1620, 1578,
1477, 1006, 769.
Anal. Calcd. for C16H9N4O2Br (369.2): C, 52.06; H, 2.46, N;
15.18. Found C, 51.97; H, 2.22; N, 15.06.
This compound was prepared in a similar way as compound 7a
by method F using 6b (57.0 mg). The sample for analysis was
prepared by recrystallization from 50% acetic acid. Yield 94.1
mg (97.8 %), mp 358 °C. IR (cm-1): 1651, 1612, 1512, 1476,
1340, 752.
Anal. Calcd. for C15H11N4OBr (343.2): C, 52.50; H, 3.23; N,
16.33. Found C, 52.62; H, 3.20; N, 16.06.
2-(4-Nitrophenyl)-2,3,5,10-tetrahydro[1,2,4]triazino[5,6-b]-
quinolin-3,10-diones (6c).
2-Amino-3-(4-nitrophenylazo)-1,4-dihydroquinolin-4-one (7c).
This compound was prepared in a similar way as compound 6a
by method A with using 5c (165.8 mg) and decalin (6 ml). Yield
144.7 mg (99.2 %), mp over 360 °C. IR (cm-1): 1697, 1673,
1622, 1578, 1527, 1476, 1350, 1299, 854.
Anal. Calcd. for C16H9N5O4 (335.3): C, 57.32; H, 2.71; N,
20.89. Found C, 57.18; H, 2.56; N, 20.68.
This compound was prepared in a similar way as compound 7a
by method F using 6c (73.5 mg). The sample for analysis was
prepared by recrystallization from 50 % acetic acid. Yield 62.2
mg (91.7 %), mp over 360 °C. IR (cm-1): 1654, 1615, 1519,
1477, 1328, 750.
Anal. Calcd. for C15H11N5O3 (309.3): C, 58.25; H, 3.58; N,
22.64. Found C, 58.34; H, 3.40; N, 22.42.
This research was supported by Postdoc grant No.
204/01/P117 of Grant agency of the Czech Republic and by the
grant of the Ministry of Education, Youth and Sports No CEZ:
MSM 153100008.
2-Amino-3-phenylazo-1,4-dihydroquinolin-4-one (7a).
Method F.
Compound 6a (13.4 mg, 0.046 mmol) was dissolved in a solu-
tion (10 ml) of NaOH (cca 200 mg). This blood red colored solu-
tion was refluxed for 45 min to obtain an orange solution. Upon
cooling, the mixture was neutralized with diluted acetic acid.
Precipitated solid was collected by filtration, washed with water
and dried. Sample for analysis was prepared by recrystallization
from DMF. Yield 11.0 mg (90.1 %), mp 225-228 °C dec. 1H
NMR: d 7.20 (t, 1H, arom.); 7.27-7.33 (m, 2H, arom.); 7.47 (t,
2H, arom.); 7.55 (t, 1H, arom.); 7.71 (d, 2H, arom.); 8.10 (d, 1H,
arom.). 15N NMR: d 45.4; 115.0. IR (cm-1): 3262, 3132, 1648,
1609, 1540, 1506, 1474, 1455, 754, 569.
REFERENCES AND NOTES
[1] Part 28 of "Cyclization Reactions of Hydrazones" series. For
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21.20. Found C, 67.91; H, 4.31; N, 20.95.
Method C.
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A solution of aniline (93 mg, 1.00 mmol) in a mixture of ice
water (5 ml) and 35% hydrochloric acid (0.6 ml) was diazotized
with a solution of sodium nitrite (69 mg, 1.00 mmol) in ice water
(2 ml). The mixture was stirred in an ice bath for 15 min and then
added portion wise to a suspension of 2-amino-1,4-dihydro-
quinolin-4-one (1) (160.2 mg, 1.00 mmol) in pyridine (40 ml),
which was pre-cooled to 0–5 °C. The mixture was stirred for 5
hours and left to stand at 0–5 °C overnight. Then, the reaction
mixture was diluted with ice water (150 ml). The precipitated
orange solid was collected by suction, washed with water and
suspended in a solution of 1 M NaOH (20 ml). Undissolved solid
was collected again by suction, washed thoroughly with water
and dried. Yield 204.3 mg (77.3 %). Spectral data were identical
to the data of the compound prepared by method A