3-Aryl- and 2,3-diaryl-4-oxo-4,5,6,7-tetrahydroindazoles. 2. Reactions of aryl- and tosylhydrazones of dimedone and 1,3-cyclohexanedione with some aromatic and heteroaromatic aldehydes

Article abstract of DOI:10.1007/s10593-006-0010-9

The reactions of the phenylhydrazone and 2-chlorophenyl-, 2,4-difluorophenyl-, 4-nitrophenyl-, and 2-pyridylhydrazones of dimedone with benzaldehyde, 4-bromo-, 4-fluoro-, 4-(dimethylamino)-, 4-nitrobenzaldehydes, 2-, 3-, and 4-pyridinecarbaldehydes and 2-

Full text of DOI:10.1007/s10593-006-0010-9

Chemistry of Heterocyclic Compounds, Vol. 41, No. 11, 2005
3-ARYL- AND 2,3-DIARYL-4-OXO-4,5,6,7-TETRA-
HYDROINDAZOLES. 2*. REACTIONS OF ARYL-
AND TOSYLHYDRAZONES OF DIMEDONE AND
1,3-CYCLOHEXANEDIONE WITH SOME AROMATIC
AND HETEROAROMATIC ALDEHYDES
I. Strakova, A. Strakovs, and M. Petrova
The reactions of the phenylhydrazone and 2-chlorophenyl-, 2,4-difluorophenyl-, 4-nitrophenyl-, and
2-pyridylhydrazones of dimedone with benzaldehyde, 4-bromo-, 4-fluoro-, 4-(dimethylamino)-,
4-nitrobenzaldehydes, 2-, 3-, and 4-pyridinecarbaldehydes and 2-thiophenecarbaldehyde have given
24 novel 2,3-diaryl-4-oxo-4,5,6,7-tetrahydroindazoles. Treatment of the tosylhydrazones of dimedone
and 1,3-cyclohexanedione with pyridine- and thiophenecarbaldehydes yielded 7 novel 3-pyridyl- and
3-thienyl-4-oxo-4,5,6,7-tetrahydroindazoles.
Keywords: arylhydrazones and tosylhydrazones of 1,3-cyclohexanedione, 3-aryl- and 2,3-diaryl-4-oxo-
4,5,6,7-tetrahydroindazoles, substituted benzaldehydes, pyridine- and thiophenecarbaldehydes.
In extending studies [1] of the synthesis of 3-aryl- and 2,3-diaryl-4-oxo-4,5,6,7-tetrahydroindazoles we
have concentrated attention in the present work on varying the aryl groups on N(2) in the 2,3-diarylindazoles and
the introduction of heteroaromatic groups at C(3) in the 3-aryl- and 2,3-diarylindazoles.
As in [1, 2] we have used the reaction of the enehydrazines 1 with substituted benzaldehydes, 2-, 3-, and
4-pyridinecarbaldehydes and 2-thiophenecarbaldehyde to synthesize the 2,3-diaryl-4-oxo-4,5,6,7-
tetrahydroindazoles.
The enehydrazines 1a,b were prepared using the method in [2].
Synthesis of compounds 1c-e was carried out by heating equimolar amounts of dimedone 2a and
2-chloro-, 2,4-difluoro-, or 4-nitrophenylhydrazines in acetic acid and the enehydrazine 1f by heating the
pyridylhydrazine in ethanol. The proton signal at C(2) absorbs in the range 4.84-4.95 ppm for these compounds
and the NH protons have a chemical shift of 7.77-9.07 ppm.
As in the studies [1, 3] the reactions of the enehydrazines 1a-f with the aldehydes were carried out by
heating in DMSO in the presence of piperidine acetate. Losses on crystallization markedly lowered the yields of
the 2,3-diarylindazoles 3a-w (see Table 1), particularly for the reactions involving the 4-nitrophenylhydrazone
1e.
_______
* For Communication 1 see [1].
__________________________________________________________________________________________
Riga Technical University, Riga LV-1048, Latvia; e-mail: marina@osi.lv. Translated from Khimiya
Geterotsiklicheskikh Soedinenii, No. 11, pp. 1669-1675, November, 2005. Original article submitted March 19,
2002.
0009-3122/05/4111-1405©2005 Springer Science+Business Media, Inc.
1405

R
R
R
OH
NHNHAr
H2NNHAr
+
R
O
O
2a,b
1a–f
Ar1CHO
+
H2NNHTs
NHNHTs
_
H2O, –H2
R
R
R
N
N
Ar
R
Ar 1
O
O
3a–w
5a,b
Ar1CHO
+
R
_
N
–
MeC6H4SO2H
N
R
R
H
N
Ar 1
N
R
O
Ar 1
6a–d
O
4a–g
1,2,5 a R = Me, b R = H, 1c-f R = Me, a,b Ar = Ph, c Ar = C6H4Cl-2, d Ar = C6H3F2-2,4,
e Ar = C6H4NO2-4, f Ar = 2-C5H4N; 3a-d, i-w R = Me, e-h R = H, a-h Ar = Ph,
i-m Ar = C6H4Cl-2, n-o Ar = C6H3F2-2,4, p Ar = C6H4NO2-4, q-w Ar = 2-C5H4N,
a,e,t Ar1 = 2-C5H4N, b,f,u Ar1 = 3-C5H4N, c,g,m,v Ar1 = 4-C5H4N, d,h,w Ar1 = 2-C4H3S,
i,n,p,q, Ar1 = Ph, j Ar1 = C6H4Br-4, k,o,s Ar1 = C6H4NMe2-4, l Ar1 = C6H4NO2-4,
r Ar1 = C6H4F-4; 4,6a-d R = Me, e-g R = H, a Ar1 = 2-C5H4N, b,e Ar1 = 3-C5H4N,
c,f Ar1 = 4-C5H4N, d,g Ar1 = 2-C4H3S
The carbonyl group absorption bands for the 2,3-disubstituted 4-oxo-4,5,6,7-tetrahydroindazoles 3
appear in the region 1675-1655 cm-1. The 1H NMR spectra show proton signals for all of the structural fragments
of the indazoles 3a-w (Table 2).
In order to synthesize the 3-aryl-4-oxo-4,5,6,7-tetrahydroindazoles 4 which are unsubstituted on the
nitrogen atom we have used the known enehydrazines 5 [1] which were prepared from the cyclohexanediones
2a,b and tosylhydrazine. Reaction of these with pyridine- and thiophenecarbaldehydes using the method [1]
gave the 3-pyridyl- and 3-thienyl-4-oxo-4,5,6,7-tetrahydroindazoles 4.
The IR spectra of the 3-(3-pyridyl)indazoles 4b,e and 3-(4-pyridyl)indazoles 4c,f show typical strong
N+H absorption in the range 2800-2500 cm-1 which may point to a marked contribution from the betaine form 6.
By contrast with the 3-(2-thienyl)indazoles 4d,g and 4-oxo-3-phenyl-4,5,6,7-tetrahydroindazoles [1], the
absorption of these compounds in the 3300-3100 cm-1 region is low. The 1H NMR spectroscopic data for 4b,c,e,f
cannot confirm these proposals, however. The resonances observed for the 3- and 4-pyridyl substituent protons
(Table 2) correspond more to a nonprotonated pyridine (δ 8.11-8.61 ppm) while the signals when they are
protonated on the N atom would be at lower field (δ 8.50-9.23 ppm) [4].
1406

TABLE 1. Characteristics of the Compounds Synthesized
Found, %
——————
Calculated, %
Com-
pound
Empirical
formula
mp, °С
Yield, %
С
Н
N
5
Cl (S)
6
1
1c
1d
1e
1f
2
3
4
7
8
83
C14H17ClN2O
C14H16F2N2O
C14H17N3O3
C13H17N3O
C20H19N3O
C20H19N3O
C20H19N3O
C19H18N2OS
C18H15N3O
C18H15N3O
C18H15N3O
C17H14N2OS
C21H19ClN2O
C21H18BrClN2O
C23H24ClN3O
C21H18ClN3O3
C20H18ClN3O
C21H18F2N2O
C23H23F2N3O
C21H19N3O3
C20H19N3O
C20H18FN3O
C22H24N4O
C19H18N4O
C19H18N4O
C19H18N4O
C18H17N3OS
C14H15N3O
C14H15N3O
C14H15N3O
63.34
63.51
63.35
63.14
61.21
61.08
67.31
67.50
75.48
75.68
75.55
75.68
75.79
75.68
70.57
70.78
74.48
74.72
74.55
74.72
74.90
74.72
69.15
69.36
71.67
71.89
58.50
58.69
69.90
70.13
63.53
63.72
68.08
68.28
71.41
71.58
69.70
69.86
69.62
69.79
75.46
75.68
71.41
71.62
73.13
73.30
71.46
71.68
71.50
71.68
71.50
71.68
66.96
66.85
69.60
69.69
69.47
69.69
69.79
69.69
6.40
6.47
10.56
10.58
13.60
13.39
216-217
175-177
232-233
200-202
173-175
166-167
166-167
150-151
126-127
150-151
168-169
114-115
168-169
178-180
227-229
180-182
126-127
125-126
160-161
172-173
175-176
163-165
210-211
168-170
162-163
158-159
124-126
160-162
165-167
235-237
6.09
6.06
10.35
10.52
93
48
67
50
50
43
58
20
43
46
34
57
47
51
46
33
56
32
48
42
30
52
22
25
25
20
30
38
78
6.29
6.23
15.10
15.26
7.27
7.41
18.00
18.17
3a
3b
3c
3d
3e
3f
6.00
6.03
13.11
13.24
5.91
6.03
13.03
13.24
5.88
6.03
13.08
13.24
5.55
5.63
8.51
8.69
(9.70)
(9.94)
5.10
5.23
14.36
14.52
5.03
5.23
14.30
14.52
3g
3h
3i
5.08
5.23
14.48
14.52
4.70
4.79
9.33
9.52
(10.60)
(10.89)
9.90
10.10
5.35
5.46
7.79
7.98
3j
4.05
4.22
6.36
6.52
3k
3l
6.06
6.14
10.46
10.67
8.80
9.00
8.70
8.96
9.90
10.08
4.40
4.58
10.70
10.62
3m
3n
3o
3p
3q
3r
3s
5.11
5.16
11.77
11.94
5.00
5.15
7.76
7.95
5.75
5.86
10.45
10.63
5.17
5.30
11.50
11.63
6.01
6.03
13.10
13.24
5.50
5.41
12.48
12.53
6.60
6.71
15.66
15.54
3t
5.59
5.70
17.40
17.60
3u
3v
3w
4a
4b
4c
5.71
5.70
17.44
17.60
5.60
5.70
17.66
17.60
5.21
5.30
12.87
12.99
(9.70)
(9.91)
6.11
6.27
17.23
17.42
6.20
6.27
17.50
17.42
6.33
6.27
17.40
17.42
1407

TABLE 1 (continued)
1
2
3
4
5
6
7
8
4d
C13H14N2OS
C12H11N3O
C12H11N3O
C11H10N2OS
63.21
63.39
67.66
67.59
67.40
67.59
60.45
60.53
5.60
5.73
5.22
5.20
5.07
5.20
4.64
4.62
11.42
11.37
19.50
19.71
19.55
19.71
12.68
12.83
(12.80)
(13.02)
220-221
218-219
235 (subl.)
84
76
83
69
4e
4f
4g
(14.50) 235 (subl.)
(14.69)
TABLE 2. IR and 1H NMR Spectra of the Compounds Synthesized
IR spectrum,
Com-
pound
1Н NMR spectrum, δ, ppm (J, Hz)*
ν, cm-1
1
2
3
1c
1610;
3250-3210
1.04 (6H, s, 2CH3); 2.01 (2H, s, CH2); 2.24 (2H, s, CH2);
4.95 (1H, s, =CH); 6.75 (2H, m, С6Н4); 6.95-7.31 (2Н, m, С6Н4);
7.77 (1Н, br. s, NH); 8.82 (1Н, br. s, NH)
1d
1e
1f
1608;
3250, 3210
1.01 (6H, s, 2CH3); 2.02 (2H, s, CH2); 2.22 (2H, s, CH2);
4.88 (1H, s, =CH); 7.04 (2Н, m, С6Н3); 7.51 (1Н, m, C6H3);
8.33 (br. s, NH); 8.75 (br. s, NH)
1610;
3240-3210
1.03 (6H, s, 2CH3); 1.95 (2H, s, CH2); 2.22 (2H, s, CH2);
4.84 (1H, s, =CH); 6.71 (2H, m, 3J = 8, С6Н4);
8.04 (2Н, m, 3J = 8, С6Н4); 8.91 (1Н, br. s, NH); 9.07 (1Н, br. s, NH)
1612;
3220, 3190,
3130
0.96 (6H, s, 2CH3); 1.93 (2H, s, CH2); 2.20 (2H, s, CH2);
4.93 (1H, s, =CH); 6.47 (1H, d, 3J = 8, С5Н4N); 6.67 (1H, dd, 3J = 8,
3J = 5, С5Н4N); 7.51 (1H, ddd, 3J = 8, 3J = 5, 4J = 1, С5Н4N);
8.02 (1Н, d, 3J = 5, С5Н4N); 8.44 (1Н, br. s, NH); 8.73 (1Н, br. s, NH)
3a
3b
1665
1672
1.09 (6H, s, 2CH3); 2.37 (2H, s, CH2); 2.80 (2H, s, CH2);
7.21 (6H, m, C6H5, С5Н4N); 7.71 (2H, m, С5Н4N);
8.40 (1Н, dt, 3J = 5, 4J = 1.5, С5Н4N)
1.09 (6H, s, 2CH3); 2.35 (2H, s, CH2); 2.80 (2H, s, CH2);
7.16-7.31 (6H, m, C6H5, С5Н4N); 7.80 (1H, dt, 3J = 8, 4J = 2, С5Н4N);
8.40 (1Н, dd, 4J = 2, 4J = 1.5, С5Н4N);
8.53 (1Н, dd, 3J = 4.5, 4J = 1.5, С5Н4N)
3с
1672
1665
1.13 (6H, s, 2CH3); 2.40 (2H, s, CH2); 2.78 (2H, s, CH2);
7.24 (7H, m, C6H5, С5Н4N); 8.51 (2Н, m, 3J = 6, С5Н4N)
3d
1.05 (6H, s, 2CH3); 2.36 (2H, s, CH2); 2.75 (2H, s, CH2);
6.93 (1H, dd, 3J = 5, 3J = 3.5, С4Н3S); 7.27 (6Н, m, С6Н5, С4Н3S);
7.51 (1Н, dd, 3J = 3.5, 4J = 1.5, С4Н3S)
3e
3f
1670
1674
2.09-3.05 (6H, m, 3CH2); 7.18-7.27 (6H, m, С6Н5, С5Н4N);
7.46 (2H, m, С5Н4N); 8.40 (1Н, m, С5Н4N)
2.02-3.05 (6H, m, 3CH2); 7.27 (6Н, m, С6Н5,С5Н4N);
7.71 (1Н, dt, 3J = 8, 4J = 1.5, С5Н4N); 8.38 (1H, d, 4J = 1.5, С5Н4N);
8.53 (1H, dd, 3J = 5, 4J = 1.5, С5Н4N)
3g
1674
2.09-3.05 (6H, m, 3CH2); 7.24 (7Н, m, С6Н5, С5Н4N);
7.67 (2Н, m, 3J = 5, С5Н4N)
3h
3i
1664
1675
2.09-2.96 (6H, m, 3CH2); 6.91-7.49 (8Н, m, С6Н5, С4Н3S)
1.09 (6H, s, 2CH3); 2.36 (2Н, s, СН2); 2.75 (2H, s, CH2);
7.20 (9Н, m, С6Н5, C6H4)
3j
1678
1673
1.06 (6H, s, 2CH3); 2.37 (2Н, s, СН2); 2.78 (2H, s, CH2);
7.11-7.42 (8H, m, 2С6Н4)
3k
1.06 (6H, s, 2CH3); 2.33 (2Н, s, СН2); 2.73 (2H, s, CH2);
2.82 (6H, s, N(CH3)2); 6.46 (2H, m, 3J = 8, С6Н4); 7.16 (2H, m, 3J = 8,
С6Н4); 7.33 (4H, m, С6Н4)
3l
1670
1.11 (6H, s, 2CH3); 2.37 (2Н, s, СН2); 2.81 (2H, s, CH2);
7.37 (4H, m, С6Н4); 7.49 (2H, m, 3J = 8, С6Н4);
8.07 (2H, m, 3J = 8, С6Н4)
1408

TABLE 2 (continued)
1
2
3
3m
1670
1.11 (6H, s, 2CH3); 2.42 (2Н, s, СН2); 2.80 (2H, s, CH2);
7.20 (2H, m, 3J = 6, С5Н4N); 7.33 (4H, m, С6Н4);
8.49 (2H, m, 3J = 6, С5Н4N)
3n
3o
3p
1672
1672
1670
1.04 (6H, s, 2CH3); 2.36 (2Н, s, СН2); 2.73 (2H, s, CH2);
6.82-7.26 (8H, m, С6Н5, С6Н3)
1.09 (6H, s, 2CH3); 2.36 (2Н, s, СН2); 2.73 (2H, s, CH2); 2.84 (6H, s,
N(CH3)2); 6.51-7.47 (7H, m, С6Н4, С6Н3)
1.06 (6H, s, 2CH3); 2.37 (2Н, s, СН2); 2.83 (2H, s, CH2);
7.27 (5H, m, С6Н5); 7.29 (2H, m, 3J = 8, С6Н4);
8.11 (2H, m, 3J = 8, С6Н4)
3q
3r
3s
1670
1668
1668
1.13 (6H, s, 2CH3); 2.36 (2Н, s, СН2); 2.82 (2H, s, CH2);
7.11-7.73 (8H, m, C6H5, С5Н4N); 8.37 (1H, m, С5Н4N)
1.07 (6H, s, 2CH3); 2.37 (2Н, s, СН2); 2.78 (2H, s, CH2);
6.89-7.76 (7H, m, C6H4, С5Н4N); 8.36 (1H, dd, 3J = 5, 4J = 1.5, С5Н4N)
1.07 (6H, s, 2CH3); 2.36 (2Н, s, СН2); 2 .81 (2H, s, CH2);
2.93 (6H, s, N(CH3)2); 6.56 (2H, m, 3J = 8, С6Н4);
7.10-7.25 (4H, m, C6H4, С5Н4N); 7.58 (1H, dt, 3J = 8, 4J = 2, С5Н4N);
8.54 (1H, dt, 3J = 5, 4J = 2, С5Н4N)
3t
1674
1672
1669
1.03 (6H, s, 2CH3); 2.36 (2Н, s, СН2); 2.81 (2H, s, CH2);
7.16-8.31 (8H, m, 2С5Н4N)
3u
3v
1.09 (6H, s, 2CH3); 2.38 (2Н, s, СН2); 2.81 (2H, s, CH2);
7.13-8.53 (8H, m, 2С5Н4N)
1.04 (6H, s, 2CH3); 2.38 (2Н, s, СН2); 2.81 (2H, s, CH2);
7.24-7.82 (5H, m, 2С5Н4N); 8.28 (1H, m, С5Н4N);
8.53 (2H, m, С5Н4N)
3w
4a
4b
1665
1.09 (6H, s, 2CH3); 2.38 (2Н, s, СН2); 2.76 (2H, s, CH2);
6.97-7.80 (6H, m, С5Н4N, C4H3S); 8.40 (1H, m, С5Н4N)
1626;
3150-3050
1.03 (6H, s, 2CH3); 2.42 (2Н, s, СН2); 2.81 (2H, s, CH2);
7.27-9.08 (4H, m, С5Н4N); 12.28 (1H, br. s, NH)
1630;
3140-3050
1.03 (6H, s, 2CH3); 2.36 (2Н, s, СН2); 2.67 (2H, s, CH2);
7.31 (1H, dd, 3J = 5, 3J = 8, С5Н4N); 8.57 (2H, m, С5Н4N);
9.27 (1H, d, 4J = 2, С5Н4N); 12.56 (1H, br. s, NH)
4с
4d
4e
1630;
3150-3050
0.97 (6H, s, 2CH3); 2.33 (2Н, s, СН2); 2.72 (2H, s, CH2);
8.11 (2H, m, 3J = 5, С5Н4N); 8.67 (2H, m, 3J = 5, С5Н4N);
10.82 (1H, br. s, NH)
1635;
3110-3050
0.97 (6H, s, 2CH3); 2.31 (2Н, s, СН2); 2.67 (2H, s, CH2);
7.11 (1H, dd, 3J = 3.8, 3J = 5, С4Н3S); 7.44 (1H, dd, 3J = 5, 4J = 1,
С4Н3S); 8.31 (1H, dd, 3J = 3.8, 4J = 1, С4Н3S); 13.25 (1H, br. s, NH)
1628;
3140-3050
2.01-2.92 (6Н, m, 3СН2); 7.31 (1H, dt, 3J = 8, 4J = 1.5, С5Н4N);
7.42 (1H, dd, 3J = 5, 3J = 8, С5Н4N); 8.56 (1H, dd, 3J = 5, 4J = 1.5, С5Н4N);
9.14 (1H, d, 4J = 1.5, С5Н4N); 13.50 (1H, br. s, NH)
4f
1630;
3150-3050
1630;
3150-3050
2.11-2.89 (6Н, m, 3СН2); 8.11 (2H, m, 3J = 5, С5Н4N);
8.61 (2H, m, 3J = 5, С5Н4N); 13.20 (1H, br. s, NH)
4g
1.97-2.89 (6Н, m, 3СН2); 7.08 (1H, dd, 3J = 4, 3J = 5, С4Н3S);
3
4
7.50 (1H, dd, J = 5, J = 1.5, С4Н3S);
3 4
8.31 (1H, dd, J = 4, J = 1.5, С4Н3S); 13.25 (1H, br. s, NH)
_______
* Spectra recorded in CDCl3 (compounds 3a-w, 4a,b,f) or in DMSO-d6
(compounds 1c-f, 4c-e,g).
EXPERIMENTAL
IR spectra were recorded on a Specord 75-IR instrument for suspensions in vaseline oil (1800-1500 cm-1
region) or in hexachlorobutadiene (3600-2000 cm-1 region). Only the carbonyl frequency is reported in the range
1800-1500 cm-1. The frequencies for the C–H stretching vibrations in the range 3050-2800 cm-1 are not given.
1H NMR spectra were recorded on a Bruker WH/90DS (90 MHz) instrument with TMS as internal standard.
1409

The hydrazines and aldehydes used in this work came from the "Acros" company.
3-(2-Chlorophenylhydrazino)-5,5-dimethylcyclohex-2-en-1-one (1c) and 3-(2,4-Difluorophenyl-
hydrazino)-5,5-dimethylcyclohex-2-en-1-one (1d). A mixture prepared from the corresponding arylhydrazine
hydrochloride (20 mmol), water (10 ml), KOH (1.12 g, 20 mmol), and acetic acid (10 ml) was added with
stirring to dimedone (2.80 g, 20 mmol) in acetic acid (20 ml). The reaction mixture was heated on a refluxing
water bath for 30 min. After 1 day the precipitated enehydrazine was filtered off and recrystallized from 60%
ethanol.
5,5-Dimethyl-3-(4-nitrophenylhydrazino)cyclohex-2-en-1-one (1e). A solution of 4-nitrophenyl-
hydrazine (1.53 g, 10 mmol) in acetic acid (5 ml) was added to a solution of dimedone (1.40 g, 10 mmol) in
acetic acid (5 ml). The precipitated nitrophenylhydrazone was filtered off and recrystallized from ethanol.
5,5-Dimethyl-3-(2-pyridylhydrazino)cyclohex-2-en-1-one (1f). A solution of 2-pyridylhydrazine
(3.27 g, 30 mmol) in ethanol (20 ml) was added dropwise to a solution of dimedone (4.20 g, 30 mmol) in ethanol
(20 ml). The mixture was heated for 15 min at 60-70°C with stirring. Water (15 ml) was added to the hot
mixture. After 1 day the precipitated product 1f was filtered off, washed on the filter with 30% aqueous ethanol,
and recrystallized from a mixture of methanol and water (2:1).
2,3-Diaryl-6,6-dimethyl-4-oxo- and 2,3-Diaryl-4-oxo-4,5,6,7-tetrahydroindazoles 3a-w. Glacial
acetic AcOH (0.2 ml), piperidine (0.4 ml), and the corresponding aldehyde (or its solution in DMSO) (4 mmol)
were added to a solution of the enehydrazine 1 (4 mmol) in DMSO (5 ml). The mixture was heated for 2 h on a
refluxing water bath, cooled, and poured into water (50 ml). The precipitated indazole 3 was filtered off,
thoroughly washed on the filter with water, and recrystallized from ethanol (3a-d,h,n-p), 50-60% ethanol
(3e-g,i-m,q-s), or a 1:5 mixture of benzene and hexane (3t-w).
3-Aryl-4-oxo-4,5,6,7-tetrahydroindazoles 4a-g. Glacial acetic acid (0.2 ml), piperidine (0.4 ml), and
the corresponding aldehyde (or its solution in DMSO) (4 mmol) were added to a solution of the tosylhydrazone
(4 mmol) in DMSO (5 ml). The mixture was heated for 2 h on a refluxing water bath, cooled, and poured into
water (50 ml). The precipitated indazole 4 was filtered off and recrystallized from a 1:5 mixture of benzene and
hexane (4a,b) or from ethanol (4c-g).
REFERENCES
1.
2.
3.
4.
I. Strakova, A. Strakovs, and M. Petrova, Khim. Geterotsikl. Soedin., 1662 (2005).
H.-J. Teuber, E. Worbs, and D. Cornelius, Chem. Ber., 101, 3918 (1968).
H.-J. Teuber and R. Braun, Chem. Ber., 100, 1353 (1967).
P. Clerc and S. Simon, Tables of Spectral Data for Structural Determination of Organic Compounds,
Springer-Verlag, Berlin (1989), H 275.
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