Synthesis and oxidation of 1,3-diamino- and 1-amino-3-azidoindazoles

Article abstract of DOI:10.1023/A:1011600420626

The animation of 3-amino- and 3-azidoindazoles by hydroxylamine-O-sulfonic acid in an alkaline medium yields previously unreported 1,3-diamino- and 1-amino-3-azidoindazoles. These products undergo slow autoxidation in chloroform solution to give 4-aminobe

Full text of DOI:10.1023/A:1011600420626

Chemistry of Heterocyclic Compounds, Vol. 37, No. 5, 2001
SYNTHESIS AND OXIDATION
OF 1,3-DIAMINO- AND
1-AMINO-3-AZIDOINDAZOLES
O. V. Dyablo, A. F. Pozharskii, V. V. Kuz'menko, and M. A. Kolesnichenko
The amination of 3-amino- and 3-azidoindazoles by hydroxylamine-O-sulfonic acid in an alkaline
medium yields previously unreported 1,3-diamino- and 1-amino-3-azidoindazoles. These products
undergo slow autoxidation in chloroform solution to give 4-aminobenzo-1,2,3-triazine. The action of
formic or acetic acid on 3-amino-1-benzylideneaminoindazole leads to recyclization and formation of
3-amino-2-benzylindazole, which is also formed in the catalytic hydrogenation of 1-benzylamino-3-
nitro- and 1-benzylideneamino-3-nitroindazoles.
Keywords:
1-amino-3-azidoindazole,
4-aminobenzo-1,2,3-triazine,
3-amino-2-benzylindazole,
1,3-diaminoindazole, autoxidation.
1-Aminoindazole (1a) and its 3-methyl, 3-phenyl, and 3-methoxy derivatives 1b-d are oxidized by lead
tetraacetate to give benzo-1,2,3-triazines 3a-d [1, 2]. This reaction presumably proceeds through the
corresponding N-nitrenes 2a-2d, which are stabilized by ring expansion as discussed in our previous work [3].
1-Amino-3-haloindazoles 1e display special behavior [4]. The action of lead tetraacetate on these rather unstable
compounds gives complex mixtures of undetermined compounds, while they undergo slow autoxidation in
chloroform solution to give 4-(3-haloindazol-1-yl)aminobenzo-1,2,3-triazines 4e, probably as the result of
aminodehalogenation of intermediate 4-halobenzo-1,2,3-triazines 3e by the action of the starting amine. The
reaction is complete in 72-120 h and the yield of 4e is 16-27%. 1-Amino-3-nitroindazole (1f) is unaltered in
chloroform solution [5]. Hence, it was of interest to study the behavior of previously unreported 1,3-diamino-
(1g) and 1-amino-3-azidoindazoles (1h).
R
N
R
R
N
R
N
oxidation
1e
N
N
NH
N
N
for R = Hal
N
N
.
N
N
.
..
N
NH2
3a–g
2a–h
1a–h
N
4e
1-4 a R = H; b R = Me; c R = Ph; d R = OMe; e R = Cl, Br, I;
f R = NO ; R = NH ; h R = N
g
2
2
3
__________________________________________________________________________________________
Rostov State University, Rostov-on-Don, 344090 Russia; e-mail: ODyablo@chimfak.rsu.ru. Translated
from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 619-625, May, 2001. Original article submitted
July 7, 1999.
0009-3122/01/3705-0567$25.00©2001 Plenum Publishing Corporation
567

The electrophilic amination of 3-aminoindazole 5a by hydroxylamino-O-sulfonic acid (HASA) in
aqueous alkali led to 1,3-diaminoindazole 1g in 10% yield. Such a low yield may be attributed both to the
difficulty of amination of amine 5a, probably due to its incomplete conversion to the N-anion, and the difficulty
in separating the reaction product from the starting compound, requiring fractional crystallization. The actual
yield of diamine 1g reaches 21% as indicated by the isolation of its benzylidene derivative 6 in this yield upon
heating the crude reaction mixture with benzaldehyde in acetic acid at reflux. The structure of 6 was proved by
its synthesis through the catalytic hydrogen hydrogenation of 1-benzylideneamino-3-nitroindazole (7) in 88%
yield described in our previous work [5]. Thus, the N-amino group in diamine 1g reacts more readily with
benzaldehyde than the 3-amino group.
R
N
H
NH2
N
NH2OSO3H
KOH
PhCHO
1g,h
AcOH
(for 1g)
N
N
N
CHPh
5a,b
6
1) H2, Pd/C, MeOH
2) PhCHO, MeOH
H2, Pd/C
MeOH
NH2
N
PhCHO
MeOH
1f
N
N
CHPh
7
1g, 5a R = NH2, 3h, 5b R = N3
We attempted to develop alternative methods for the synthesis of diamine 1g. The reduction of the nitro
group in 1-amino-3-nitroindazole 1f by excess hydrogen over 2% Pd/C led only to the formation of
3-aminoindazole 5a. The elimination of the N-amino group probably occurs in intermediate
1,3-diaminoindazole 1g. Support for this hypothesis lies in the observation that if the reaction is stopped after
the absorption of three molar equivalents of hydrogen, diamine 1g may be isolated in 42% yield as
benzylideneamino derivative 6.
Unfortunately, the selective hydrolysis of azomethine 6 could not be carried out to give diamine 1g. In
contrast to similar compounds [3], the hydrolysis of azomethine 6 in 4% hydrochloric acid does not proceed,
while the elimination of the benzylidene group occurs in more acidic media at 20-100°C to give only
3-aminoindazole 5a.
NO2
NH2
N
H2, Pd/C
MeOH
RCO2H
20 °C
6
CH2Ph
N
N
N
NHCH2Ph
8
NaBH4/ i-PrOH
or
9
H2, Pd/C
LiAlH4/Et2O
NaBH4
i-PrOH
MeOH, 55 °C
or
NH2
RCO2H, 20 °C
7
N
N
NHCH2Ph
10
568

In a study of the hydrolysis of azomethine 6 in formic or acetic acid, previously unreported 3-amino-2-
benzylindazole (8) was isolated. Benzylindazole 8 is also formed instead of the expected 3-amino-1-
benzylaminoindazole (10) in the hydrogenation of 1-benzylamino-3-nitroindazole (9), which was obtained by
the action of sodium borohydride on 1-benzylideneamino-3-nitroindazole (7) in 2-propanol. We should note that
NaBH4 and LiAlH4 do not reduce the benzylideneamino group in 3-amino-1-benzylideneaminoindazole 6 and,
thus, 3-amino-1-benzylaminoindazole 10 could not be prepared. This behavior should be attributed to prior
ionization of the 3-amino group to the N-anion, which is inert to subsequent reduction.
NH2
NH
NH
+
H2
NH2
H2, Pd/C
MeOH
H
7
6
NH
N
N
N
.
.
CHPh
CH2Ph
H2N
H2N
+
NH2
+
NH2
CH2Ph
8
N
N
CH2Ph
+
– NH2
N
N
..
..
+
H2
N2 +
NH2
N–H
[HN NH]
+
– H
Benzylindazole 8 is also formed in 10% yield in the catalytic hydrogenation of 1-benzylideneamino-3-
nitroindazole 7 in methanol at room temperature; 3-amino-1-benzylideneaminoindazole 6 is also formed. When
the reaction temperature is raised to 55°C, the yield of 8 rises to 75%. The reduction of 7 in formic or acetic
acid also leads to an enhanced yield of 3-amino-2-benzylindazole 8 to 45-50%. The formation of 8 appears to
recall the recently discovered rearrangement of 1-alkylaminopyrazoles and 1-alkylaminoindazoles to give
1-alkyl-5-aminopyrazoles and 2-alkyl-3-aminoindazoles, respectively [6, 7].
Evidence of the structure of 8 was provided by its independent synthesis involving the benzylation of
3-aminoindazole 5a using benzyl chloride in methanol. The yield of amine 8 was 22%. It is interesting that only
3-amino-1-benzylindazole (11) is formed in 70% yield in the benzylation of 5a in KOH/DMSO.
NH2
PhCH2Cl
MeOH
PhCH2Cl
8
5a
N
DМSО, KOH
N
CH2Ph
11
3-Azido-1-aminoindazole 1h was obtained in 20% yield by the amination of 3-azidoindazole 5b with
excess HASA analogously to diamine 1g.
The oxidation of amines 1g and 1h in chloroform solution is even slower than for 1-amino-3-
haloindazole 1e and is completed only after 37-30 days. A brown precipitate slowly formed and was identified
in both cases as 4-aminobenzo-1,2,3-triazine (12) (24-33% yield). As in the case of 1-amino-3-haloindazoles 1e,
this reaction presumably proceeds through the formation of N-nitrenes 2g and 2h, which cyclize to give
4-amino- (12) and 4-azidobenzo-1,2,3-triazines (13). Triazine 13 probably is reduced to amine 12 by reacting
with the N-amino group of the starting amine.
569

CHCl3
1g,h
2g,h
2g
2h
NH2
N3
N
N
N
N
N
2h
N
12
13
The oxidation of amines 1g and 1h by lead tetraacetate in methylene chloride leads to the formation of a
mixture of unstable compounds, which could not be purified.
Thus, our study has shown that the presence of an electron-donor substituent at C(3) is required for the
autoxidation of 1-aminoindazoles in chloroform solution. Further support for this hypothesis lies in the finding
that 1-aminoindazole 1a itself hardly changes upon maintenance in chloroform solution for 10 days.
EXPERIMENTAL
1
The IR spectra were taken on a UR-20 spectrometer in vaseline oil. The H NMR spectra were
registered on a Bruker-250 spectrometer for 1g,h, 8, 9, 11, and 12 and a Unity-300 spectrometer for 6. The UV
and mass spectra of 8 were obtained on a Perkin-Elmer UV-VIS Spectrometer Lambda 10 and Perkin-Elmer
Q-Mass 910 spectrometer, respectively. The reaction course and purity of the products were monitored by thin-
layer chromatography on alumina plates (Brockmann grade-IV activity, visualization with iodine vapor). The
melting points were obtained for samples in sealed capillary tubes and not corrected. The starting compounds
were prepared according to the following procedures: 1-amino-3-nitroindazole 1f [4], 1-benzylidenamino-3-
nitroindazole 7 [4], 3-aminoindazole 5a [8], and 3-azidoindazole 5b [9].
1,3-Diaminoindazole (1g). A solution of the sodium salt of hydroxylamine-O-sulfonic acid (HASA) in
water (10 ml) obtained by the neutralization of HASA (2.5 g, 0.022 mol) with excess NaHCO3 was added to a
solution of 3-aminoindazole 5a (1.33 g, 0.01 mol) and NaOH (2.0 g, 0.05 mol) in a mixture of water (25 ml) and
ethanol (5 ml) at 60°C. The reaction mixture was stirred for 20 min and a solution of the sodium salt of HASA
in water (5 ml) obtained by the neutralization of HASA (1.25 g, 0.011 mol) with excess NaHCO3. The mixture
was stirred for 1 h at 50°C, cooled, and extracted with two 30-ml chloroform portions. Chloroform was distilled
off and the residue was subjected to fractional crystallization from octane to give 0.15 g (10%) 1g as gray
1
needles; mp 118-120°C. IR spectrum in CDCl3, ν, cm-1: 1570, 1620 (ring), 3190, 3287, 3380 (NH2). H NMR
), δ, ppm: 3.9 (2H, br. s, disappears upon deuteration, N–NH
deuteration, C–NH2); 7.01 (1H, m, 5-H); 7.37 (2H, m, 6-H, 7-H); 7.46 (1H, m, 4-H). Found, %: C 56.42; H 5.63;
N 38.13. C7H8N4. Calculated, %: C 56.74; H 5.44; N 37.81.
spectrum (CDCl3
2); 4.9 (2H, br. s, disappears after
1-Amino-3-azidoindazole (1h). A solution of HASA (2.5 g, 0.022 mol) in water (10 ml) previously
neutralized with dry NaHCO3 was added to a solution of 3-azidoindazole 5b (1 g, 0.0063 mol) and NaOH (2 g,
0.05 mol) in water (25 ml) at 60°C. The mixture was stirred for 1 h at 55°C, cooled, and extracted with two
30-ml chloroform portions. The chloroform solution was passed through a 22×2.5-cm alumina column using
chloroform as the eluent and collecting the fraction with Rf 0.4. Evaporation of chloroform gave 0.22 g (20%)
1g as colorless needles; mp 112°C (dec., from petroleum ether). IR spectrum, , cm-1: 1595, 1620 (ring), 2120
ν
1
), δ, ppm: 5.1 (2H, br. s, disappears after deuteration, NH
(N3), 3205, 3320 (NH3). H NMR spectrum (CDCl3
2);
7.09 (1H, m, 5-H); 7.51 (1H, m, 6-H); 7.51 (2H, m, 4-H, 7-H). Found, %: C 47.82; H 3.69; N 48.65. C7H6N6.
Calculated, %: C 48.27; H 3.47; N 48.25.
570

3-Amino-1-benzylidenaminoindazole (6). A. A solution of 1-amino-3-nitroindazole 1f (0.35 g,
2 mmol) in methanol (130 ml) was shaken in a hydrogen atmosphere at 40-45°C in the presence of 2% Pd/C
(0.3 g) over 8 h. The catalyst was filtered off. A sample of benzaldehyde (0.5 ml, 5 mmol) was added to the
methanolic solution and heated at reflux for 3 h. Two thirds of methanol was distilled off. The residue was
evaporated to dryness, dissolved in chloroform (30 ml), and subjected to chromatography on a 30×2.5-cm
alumina column with chloroform as the eluent. The fraction with Rf 0.6 was collected. Chloroform was
evaporated to give 0.2 g (42%) 6 as yellow-green crystals; mp 127-129°C (1:1 octane–benzene). IR spectrum,
-1
1
), δ, ppm,
, cm : 1595, 1625 (ring), 1640 (C=N), 3095, 3200, 3310 (NH2). H NMR spectrum (CDCl3
J (Hz):
ν
4.35 (2H, br. s, disappears after deuteration, NH2); 7.13 (1H, 5-H, dt, J5,6 = 7.10); 7.40 (4H, m, 3'-H, 5'-H, 6-H);
7.50 (1H, dt, J4,5 = 8.05, 4-H); 7.73 (1H, d, J6,7 = 8.42, 7-H); 7.82 (2H, m, 2'-H, 6'-H); 8.54 (1H, s, –CH=).
Found, %: C 70.87; H 5.50; N 24.00. C14H12N4. Calculated, %: C 71.16; H 5.11; N 23.71.
B. A solution of 1-benzylideneamino-3-nitroindazole 7 (0.35 g, 1.3 mmol) in methanol (350 ml) was
shaken in a hydrogen atmosphere at room temperature in the presence of 2% Pd/C (0.3 g) for 3 h. The catalyst
was filtered off. Four fifths of methanol was distilled off. The residue was evaporated to dryness. The yellow-
green precipitate was dissolved in chloroform (30 ml) and passed through a 30×2.5-cm alumina column with
chloroform as the eluent, collecting two fractions. The first fraction with Rf 0.6 contained 0.27 g (88%) 6 as
yellow-green crystals; mp 127-129°C (1:1 octane–benzene). The second fraction with Rf 0.4 gave 0.03 g (10%)
2-benzyl-3-aminoindazole 8 as gray-green crystals, mp 139-140°C (octane).
C. A solution of the sodium salt of HASA in water (10 ml) obtained by the neutralization of HASA
(2.5 g, 0.022 mol) with excess NaHCO3 was added to a solution of 3-aminoindazole 5a (1.33 g, 0.01 mol) and
NaOH (2 g, 0.05 mol) in a mixture of water (25 ml) and ethanol (5 ml) at 60°C. The mixture was stirred for 20
min and a solution of the sodium salt of HASA in water (5 ml) obtained by the neutralization of HASA (1.25 g,
0.011 mol) with excess NaHCO3 was added. The mixture was stirred at 50°C for 1 h, cooled, and extracted with
two 30-ml chloroform portions. Chloroform was distilled off and benzaldehyde (1 ml, 0.01 mol) and ethanol
(10 ml) was added to the residue. The mixture was heated at reflux for 2 h. The solvent was evaporated to
dryness. The yellow-green crystalline precipitate formed was dissolved in chloroform (30 ml) and purified on a
30×2.5-cm alumina column with chloroform as the eluent, collecting the fraction with Rf 0.6. Evaporation of
chloroform gave 0.5 g (21%) 6 as yellow-green crystals; mp 127-129°C (1:1 octane–benzene).
Hydrolysis of 3-Amino-1-benzylideneaminoindazole (6). A suspension of 6 (0.45 g, 1.9 mmol) in
conc. hydrochloric acid (10 ml) was heated at reflux for 15 min. The solution obtained was neutralized with
conc. aqueous ammonia to pH 7 and evaporated to dryness. The residue was grinded in ethyl acetate (10 ml).
The undissolved NH4Cl was filtered off. The solution was passed through a 15×2.5-cm alumina column with
ethyl acetate as the eluent, collecting the fraction with Rf 0.3. The solvent was evaporated to give 0.25 g (99%)
3-aminoindazole (5a) as gray prisms; mp 154°C (benzene).
The hydrolysis was carried out analogously in 12% hydrochloric acid at reflux for 1 h to give 56% 5a,
in 12% hydrochloric acid at room temperature for 24 h to give 38% 5a, and in 8% hydrochloric acid at room
temperature for 120 h to give 19% 5a.
3-Amino-2-benzylindazole (8). A. A solution of 1-benzylideneamino-3-nitroindazole 7 (0.35 g,
1.3 mmol) in methanol (350 ml) was shaken for 4 h in a hydrogen atmosphere at 55°C in the presence of
2% Pd/C (0.3 g). The catalyst was filtered off and four fifths of the methanol was distilled off. The residue was
evaporated to dryness and the oil obtained was dissolved in chloroform (30 ml) and passed through a 30×2.5-cm
alumina column with chloroform as the eluent, collecting the fraction with Rf 0.4. Evaporation of chloroform
gave 0.225 g (75%) 8 as gray-green crystals; mp 139-140°C (octane). IR spectrum, , cm-1: 1560, 1635 (ring),
ν
1
), δ, ppm,
3170, 3330 (NH2). H NMR spectrum (CDCl3
J (Hz): 3.75 (2H, br. s, disappears after deuteration,
NH2); 5.42 (2H, s, CH2); 6.83 (1H, m, 5-H); 7.2 (1H, m, 6-H); 7.3 (5H, m, 2'-H, 6'-H); 7.36 (1H, d, 7-H,
3J76 = 8.45); 7.47 (1H, d, 4-H, 3J76 = 8.87). Mass spectrum, m/z (%): 223 (100) (M+), 207 (5.93) (M+ - NH2), 146
+
+
Ph), 77 (22.48) (Ph). UV spectrum (methanol), λ
(7.97) (M - Ph), 132 (41.68) (M - CH2Ph), 91 (75.47) (CH2
max
(log ε): 260 (4.12), 268 (4.04), 335 (4.39).
571

B. A solution of 3-amino-1-benzylideneaminoindazole 6 (0.1 g, 0.4 mmol) in conc. formic or acetic acid
(10 ml) was left for 24 h at room temperature, neutralized by adding conc. aqueous ammonia to pH 7, and
extracted with three 10-ml chloroform portions. The chloroform solution was passed through a 30×1.5-cm
alumina column with chloroform as the eluent, collecting the fraction with Rf 0.4. Evaporation of chloroform
gave 0.07 g (75%) 8 as light green crystals; mp 139-140°C (octane).
C. A solution of 1-benzylamino-3-nitroindazole 9 (0.134 g, 0.5 mmol) in methanol (50 ml) was shaken
for 4 h in a hydrogen atmosphere at 55°C in the presence of 2% Pd/C (0.15 g). The catalyst was filtered off and
four fifths of methanol was distilled off. The residue was evaporated to dryness. The oil obtained was dissolved
in chloroform (30 ml) and passed through a 30×2.5-cm alumina column with chloroform as the eluent,
collecting the fraction with Rf 0.4. Evaporation of chloroform gave 0.08 g (72%) 8 as gray-green crystals;
mp 139-140°C (octane).
D. A solution of 3-aminoindazole 5a (0.133 g, 1 mmol) and benzyl chloride (0.072 ml, 0.62 mmol) in
methanol (3 ml) was heated at reflux for 6 h. The solvent was evaporated to dryness. The residue was suspended
in water (5 ml) and extracted with three 3-ml chloroform portions. The chloroform extract was passed through a
20×1-cm alumina column with chloroform as the eluent, collecting the fraction with Rf 0.4. Evaporation of the
solvent gave 0.024 g (22%) 8 as gray crystals; mp 138-140°C (octane). The aqueous solution containing
3-aminoindazole hydrochloride was treated with conc. aqueous ammonia to pH 7-8. The precipitate formed was
filtered off to give 0.033 g (50%) 3-aminoindazole 5a as gray prisms; mp 153-154°C (benzene).
1-Benzylamino-3-nitroindazole (9). A sample of sodium borohydride (0.15 g, 3.9 mmol) was added in
portions to a solution of 1-benzylideneamino-3-nitroindazole 7 (1 g, 3.8 mmol) in 2-propanol (460 ml) and left
for 24 h at room temperature. Four fifths of the solvent was distilled off. The residue was diluted with water
(100 ml) and neutralized with concentrated hydrochloric acid to pH 7. The reaction mixture was extracted with
two 5-ml chloroform portions and passed through a 30×2.5-cm alumina column with chloroform as the eluent,
collecting the fraction with Rf 0.9. Evaporation of chloroform gave 0.2 g (20%) 9 as yellow crystals; mp 118°C
1H NMR spectrum, δ, ppm,
J (Hz): 4.50 (2H, d, CH2, J = 5.03); 5.55 (1H, t, NH, J = 5.02); 7.30 (4H, m, 2'-H, 6'-H); 7.40 (3H, m, 5-H,
7-H); 8.18 (1H, m, 4-H). Found, %: C 62.92; H 4.77; N 21.18. C14H12N4O2. Calculated, %: C 62.68; H 4.50;
N 20.88.
(octane). IR spectrum, , cm-1: 1389, 1520 (NO2), 1620 (ring), 3280 (NH).
ν 3
3
3-Amino-1-benzylindazole (11). A sample of 3-aminoindazole 5a (0.133 g, 1 mmol) was added to a
solution of KOH (0.14 g, 2.5 mmol) in DMSO (20 ml), stirred for 5 min, and, then, benzyl chloride (0.144 ml,
1.25 mmol) was added in a single portion. The mixture was stirred for 2 h at room temperature and diluted with
water (30 ml). The emulsion obtained was extracted with three 10-ml chloroform portions. The chloroform
extract was washed with two 10-ml water portions and passed through a 20×1.5-cm alumina column with
chloroform as the eluent, collecting the fraction with Rf 0.6. Evaporation of chloroform gave 0.158 g (70%) 11
1
), δ, ppm,
as cream-colored plates; mp 115-116°C (octane) (116°C (ethanol) [10]). H NMR spectrum (CDCl3
J (Hz): 3.75 (2H, br. s, disappears after deuteration, NH2); 5.35 (2H, s, CH2); 7.01 (1H, m, 5-H); 7.24 (7H, m,
2'-H, 6'-H, 6-H, 7-H); 7.53 (1H, m, 4-H).
4-Aminobenzo-1,2,3-triazine (12). A. A solution of 1,3-diaminoindazole 1g (0.1 g, 0.67 mmol) in
chloroform (20 ml) was left for 30 days at room temperature. A brown precipitate gradually settled from the
solution, which was filtered and washed with chloroform to give 0.032 g (33%) 12 as brown crystals; mp 270°C
(266°C [11]). IR spectrum, , cm-1: 1655 (C=N), 3151, 3399 (NH2). H NMR spectrum (DMSO-d6),
1
ν
δ,
ppm: 8.00 (1H, m, 6-H); 8.15 (2H, m, 7-H, 8-H); 8.50 (1H, m, 5-H); 9.10 (br. s, NH2, disappears after
deuteration).
B. A solution of 3-azido-1-aminoindazole 1h (0.1 g, 0.57 mmol) in chloroform (20 ml) was left for
27 days at room temperature. A brown precipitate gradually settled from the solution, which was filtered off and
washed with chloroform to give 0.02 g (24%) 12 as brown crystals; mp 270°C.
572

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