Synthesis of 2-aryl[1]benzofuro[2,3-e][1,2,4]triazin-3(2H)-ones and their use for preparation of 1-aryl-5-(2-hydroxyphenyl)-6-Azauracils

Article abstract of DOI:10.1135/cccc19971754

A series of arylhydrazones 1a-1i was prepared by coupling of arene diazonium salts with ethyl N-(benzo[b]furan-2-yl)carbamate. The hydrazones 1 were thermally cyclized to the corresponding 2-aryl[1]benzofuro[2,3-e][1,2,4]triazin-3(2H)-ones 2a-2i, derivati

Full text of DOI:10.1135/cccc19971754

1754
Styskala, Slouka, Hejsek, Bekarek:
SYNTHESIS OF 2-ARYL[1]BENZOFURO[2,3-e][1,2,4]TRIAZIN-3(2H)-ONES
AND THEIR USE FOR PREPARATION OF
1-ARYL-5-(2-HYDROXYPHENYL)-6-AZAURACILS*
1
Jakub STYSKALA , Jan SLOUKA, Miloslav HEJSEK and Vojtech BEKAREK
Department of Organic Chemistry, Palacky University, 771 46 Olomouc, Czech Republic;
e-mail: 1styskala@risc.upol.cz
Received April 24, 1997
Accepted August 8, 1997
Dedicated to Professor Miloslav Ferles on the occasion of his 75th birthday.
A series of arylhydrazones 1a–1i was prepared by coupling of arene diazonium salts with ethyl
N-(benzo[b]furan-2-yl)carbamate. The hydrazones 1 were thermally cyclized to the corresponding
2-aryl[1]benzofuro[2,3-e][1,2,4]triazin-3(2H)-ones 2a–2i, derivatives of a new fused ring system.
Compounds 2 were transformed by hydrolytic splitting to the corresponding 1-aryl-5-(2-hydroxyphenyl)-
6-azauracils 3a–3i.
Key words: Fused Heterocycles; Diazo compounds; Hydrazones; Benzofurotriazines; 6-Azauracils.
Cyclization of N-arylcarbamates substituted in ortho position with azo or tautomeric
hydrazono group is well-tried synthesis of condensed 1,2,4-triazines. In this manner,
series of benzo[1,2,4]triazines2–7, pyrazolo[3,4-e][1,2,4]triazine8,9, [1,2,4]triazino[4,5-a]-
benzimidazole10–13 and [1,2,4]triazinoindole14,15 derivatives, were advantageously pre-
pared. In this paper we utilized this synthetic way for the preparation of
[1]benzofuro[2,3-e][1,2,4]triazine derivatives which have not been described so far.
By coupling of diazonium salts with ethyl N-(2-benzo[b]furan-2-yl)carbamate in py-
ridine, corresponding ethyl N-(3-arylazobenzo[b]furan-2-yl)carbamates 1-A or their hy-
drazono-tautomeric form 1-B (Scheme 1) were prepared in good yields. In addition to
the phenyl derivative 1a, a series of para substituted derivatives with +I effect (1b), +M
effect (1c–1g) and –M effect (1h, 1i) were prepared in this way. As expected, com-
pounds 1h and 1i were obtained in the highest yields.
The azo–hydrazone tautomerism with phenyl derivative 1a was studied by IR spec-
troscopy in tetrachloromethane solution. For this purpose, compound 1a containing la-
* Part XXIV in the series Cyclization Reactions of Hydrazones; Part XXIII: see ref.1.
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

Synthesis of Arylbenzofurotriazines
1755
belled nitrogen in position 8 was prepared from aniline-15N. It was found that the un-
labelled derivative shows in the region of N–H stretching vibrations an absorption
maximum at 3 206.4 cm–1 while the compound labelled with the isotope 15N has the
absorption maximum shifted to 3 199.5 cm–1. This shift is in accordance with the for-
~
mula ν = 1/2π(K/µ)1/2. In view of these facts we conclude that the products of coupling
exist in tetrachloromethane solution in the hydrazono form 1-B. This hydrazono form
of 1-B was confirmed unambiguously by 1H, 13C and 15N NMR spectroscopy. With this
compound, the NMR signals were assigned using 2D NMR. The determined spin–spin
coupling constants were as follows: 7.2 Hz for the interaction of hydrogen atoms in
CH3 and CH2 groups and 7.9 or 1.08 Hz for interaction between aromatic hydrogen
R
N
R
N N
N
COOC H
2
COOC H
2 5
5
O
N
H
O
N
H
1-A
6
R
R
5
7
4
1
8
N
N
N
N
3
2
N
N
H
O
O
O
R
COOC H
2
5
2
1-B
O
H
N
N
In formulae 1-3 :
O
N
H
O
R
R
1-3
1-3
3
a
b
c
d
e
f
H
CH O
3
C H O
2 5
g
h
i
CH
Cl
Br
I
3
CH CO
3
NO
2
SCHEME 1
atoms in ortho or meta position of the benzo[b]furan system. In the 15N NMR spectrum
of compound 1a with the labelled atom 15N at position 8, the chemical shift shows
unambiguously that the compound exists in the hydrazono form 1-B. This is in accord-
ance with the above mentioned IR spectral results.
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

1756
Styskala, Slouka, Hejsek, Bekarek:
TABLE I
Characteristic data of compounds 1
Calculated/Found
M.p., °C
Yield, %
Formula
M.w.
ν(C=O)
λmax
nm
Compound
log ε
cm–1
% C
% H
% N
1a
97–99
83
C
17H15N3O3
309.3
66.01
66.30
4.89
4.68
13.59
13.63
1 737.2
1 683.3
201.1
262.4
420.8
4.31
4.22
4.22
1b
1c
1d
1e
1f
124–126 C18H17N3O3
79 323.3
66.86
66.65
5.30
5.34
13.00
13.13
1 730.7
1 683.8
201.7
266.2
428.4
4.41
4.23
4.24
158–160 C17H14ClN3O3
81 343.7
59.37
59.13
4.10
3.89
12.22
12.21
1 732.5
1 692.6
201.7
263.2
419.2
4.37
4.21
4.26
138–140 C17H14BrN3O3
84 388.3
52.59
52.53
3.63
3.67
10.82
10.84
1 737.9
1 692.1
201.7
263.2
420.2
4.43
4.25
4.32
167–170 C17H14IN3O3
78 435.3
46.91
46.93
3.24
3.13
9.65
9.71
1 726.8
1 686.0
201.1
261.6
422.4
4.45
4.24
4.33
118–120 C18H17N3O4
63.71
64.45
5.05
4.95
12.38
12.54
1 738.5
1 678.9
210.9
270.4
448.8
4.77
4.21
4.15
64
339.3
1g
1h
87–90
66
C19H19N3O4
353.4
64.58
64.86
5.42
5.28
11.89
12.07
1 732.8
1 672.0
201.1
268.1
414.4
4.42
4.14
4.07
150–152 C19H14N3O4
85 351.3
64.95
64.69
4.88
5.05
11.96
12.10
1 736.9
1 672.9
201.9
260.8
287.2
424.1
4.51
4.26
3.97
4.51
1i
233–235 C17H14N4O5
89 354.3
57.62
57.35
3.98
3.83
15.81
16.07
1 736.6
1 698.2
201.5
257.6
434.4
4.47
4.13
4.53
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

Synthesis of Arylbenzofurotriazines
1757
Heating at a higher temperature, for example boiling in decalin, leads to cyclization
of all hydrazono carbamates 1 and gives corresponding 2-aryl[1]benzofuro[2,3-e]-
[1,2,4]triazin-3(2H)-ones (2a–2i). Cyclization of derivatives substituted by the groups
with –M effect proceeds more slowly than in other cases; however, 60-min boiling in
decaline is quite sufficient for nearly quantitative cyclization. Thermal cyclization of
compound 1a is well perceptible in its mass spectrum where both its molecular ion
peak m/z 309.3 and the molecular peak of product 2a, m/z 263.3, can be found. In the
mass spectrum a distinct peak corresponding to fragment C6H5N (m/z 91.1) is present,
which arose by splitting of the azo group formed by tautomeric transformation.
TABLE II
Characteristic data of compounds 2
Calculated/Found
M.p., °C
Yield, %
Formula
M.w.
ν(C=O)
λmax
nm
Compound
log ε
cm–1
% C
% H
% N
2a
2b
2c
2d
2e
2f
210–212
89
C
15H9N3O2
263.3
68.43
68.44
3.45
3.28
15.96
16.13
1 724.7
1 672.9
375.2
379.7
376.3
379.2
380.6
390.2
391.6
379.8
381.6
4.01
4.01
4.02
4.02
4.04
4.17
4.17
4.04
4.07
195–197 C16H11N3O2
88 277.3
69.30
69.04
4.00
3.80
15.16
15.16
1 698.9
1 664.4
231–233 C15H8ClN3O2
87 297.7
60.59
60.32
2.71
2.45
14.11
14.04
1 692.5
1 665.9
243–245 C15H8BrN3O2
89 342.3
52.65
52.23
2.35
2.35
12.28
12.16
1 690.2
1 667.1
266–268 C15H8IN3O2
90 389.3
46.62
46.29
2.07
2.02
10.79
10.70
1 688.9
1 666.2
251–253 C16H11N3O3
90 293.3
65.32
65.50
3.81
3.77
14.33
14.26
1 696.7
1 667.1
2g
2h
2i
229–231 C17H13N3O3
89 307.3
66.45
66.11
2.23
2.25
13.68
13.53
1 683.9
1 666.4
275–277 C17H11N3O3
78 305.3
66.88
66.51
3.63
3.53
13.77
13.69
1 684.6
1 665.5
328–330 C15H8N4O4
79 308.3
58.44
58.01
2.62
2.47
18.18
18.03
1 696.4
1 667.6
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

1758
Styskala, Slouka, Hejsek, Bekarek:
TABLE III
Characteristic data of compounds 3
Calculated/Found
M.p., °C
Yield, %
Formula
M.w.
ν(C=O)
λmax
nm
Compound
log ε
cm–1
% C
% H
% N
3a
261–263
90
C
15H11N3O3
281.3
64.06
64.01
3.91
4.01
14.95
14.78
1 724.4
1 687.9
202.7
242.5
324.5
4.53
4.26
4.05
3b
3c
3d
3e
3f
252–254 C16H13N3O3
93 295.3
65.08
65.26
4.44
4.71
14.23
14.01
1 731.1
1 692.6
205.5
239.6
316.9
4.46
4.01
3.82
249–251 C15H10ClN3O3
92 315.7
57.14
56.86
3.19
2.95
13.33
12.96
1 733.3
1 696.1
203.6
241.6
325.1
4.43
3.96
3.77
251–253 C15H10BrN3O3
89 360.3
50.00
50.11
2.78
2.63
11.67
11.65
1 733.3
1 692.2
203.2
245.1
313.6
4.7
4.26
4.05
273–275 C15H10IN3O3
91 407.7
44.25
44.18
2.48
2.28
10.32
10.31
1 710.3
1 693.2
204.2
249.2
316.1
4.67
4.28
4.04
247–249 C16H13N3O4
90 311.3
61.73
61.83
4.21
4.16
13.51
13.26
1 721.4
1 693.9
204.1
271.8
297.6
4.38
4.03
3.86
3g
3h
3i
249–251 C17H15N3O4
92 325.3
62.76
62.56
4.65
4.98
12.92
13.05
1 722.7
1 698.4
202.5
233.1
327.2
4.4
4.01
3.73
265–267 C17H13N3O4
90 323.1
63.16
63.23
4.05
4.21
13.01
12.96
1 732.9
1 707.1
1 681.6
203.1
270.6
297.6
4.61
4.23
4.15
258–260 C15H10N4O5
88 326.3
55.21
55.45
3.07
3.19
17.18
17.11
1 735.5
1 697.6
203.6
241.6
343.2
4.56
4.25
4.01
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

Synthesis of Arylbenzofurotriazines
1759
TABLE IV
NMR spectral data of compounds 1–3
Compound Nucleus
Chemical shifts
1aa
1H
1.41 t, 3 H (CH3); 4.38 q, 2 H (CH2); 7.09 m, 1 H (H-7); 7.15 d, 1 H ((H-1);
7.22 t, 1 H (H-3); 7.30 t, 1 H (H-2); 7.34–7.42 m, 4 H (H-5,6); 7.71 d, 1 H
(H-4); 12.25 bs, 1 H (NH)
13C
14.26 (CH3); 63.14 (CH2); 111.05 (C-1); 114.97 (C-5); 119.19 (C-4); 123.02;
124.07 (C-7); 124.29; 124.57 (C-3); 128.54 (C-2); 129.41 (C-6); 142.34;
153.26; 154.33; 158.40
15N
1H
–205.8 brs (CH3NO2 int)
1b
1c
1d
1e
1f
1.34 t, 3 H (CH3); 2.40 s, 3 H (CH3-arom.); 4.29 q, 2 H (CH2); 7.34–7.46 m,
4 H; 7.56 d, 1 H; 7.72 d, 2 H; 8.19 d, 1 H; 11.50 brs, 1 H (NH)
1H
1H
1H
1H
1H
1H
1.32 t, 3 H (CH3); 4.29 q, 2 H (CH2); 7.38 t, 1 H; 7.46 t, 1 H;
7.55 m, 3 H; 7.79 d, 2 H; 8.17 d, 1 H; 11.62 brs, 1 H (NH)
1.34 t, 3 H (CH3); 4.30 q, 2 H (CH2); 7.40 t, 1 H; 7.41–7.52 m, 2 H;
7.70–7.81 m, 4 H; 8.16 d, 1 H; 11.67 brs, 1 H (NH)
1.32 t, 3 H (CH3); 4.31 q, 2 H (CH2); 7.39 t, 1 H; 7.46 t, 1 H;
7.50–7.57 m, 3 H; 7.85 d, 2 H; 8.15 d, 1 H; 11.60 brs, 1 H (NH)
1.33 t, 3 H (CH3); 3.89 s, 3 H (CH3O); 4.29 q, 2 H (CH2); 7.14 d, 2 H;
7.42 m, 2 H; 7.62 d, 1 H; 7.92 d, 2 H; 8.27 d, 1 H; 11.30 brs, 1 H (NH)
1g
1h
1.33 t, 3 H (CH3); 1.41 t, 3 H (CH3); 4.16 q, 2 H (CH2O); 4.28 q, 2 H (CH2); 7.12 d,
2 H; 7.41 m, 2 H; 7.62 d, 1 H; 7.90 d, 2 H; 8.26 d, 1 H; 11.32 brs, 1 H (NH)
1.33 t, 3 H (CH3); 2.60 s, 3 H (CH3CO); 4.32 q, 2 H (CH2); 7.38 t, 1 H;
7.44 d, 1 H; 7.52 t, 1 H; 7.67 d, 2 H; 8.05 d, 2 H; 8.10–8.25 brs, 1 H;
11.77 brs, 1 H (NH)
1i
1H
1.32 t, 3 H (CH3); 4.32 q, 2 H (CH2); 7.41 m, 2 H; 7.54 t, 1 H;
7.73 d, 2 H; 8.00–8.20 brs, 1 H; 8.32 d, 2 H; 11.86 brs, 1 H (NH)
2a
2b
2c
2d
2e
2f
1H
1H
1H
1H
1H
1H
1H
7.52–7.78 m, 8 H; 8.05 d, 1 H
2.44 s, 3 H (CH3); 7.41 d, 2 H; 7.53 m, 3 H; 7.77 q, 2 H; 8.05 d, 1 H
7.55 t, 1 H; 7.64 d, 2 H; 7.75 t, 1 H; 7.76 t, 1 H; 7.80 d, 2 H; 8.06 d, 1 H
7.54 t, 1 H; 7.65 d, 2 H; 7.76 t, 1 H; 7.78 t, 1 H; 7.81 d, 2 H; 8.06 d, 1 H
7.50 d, 2 H; 7.55 t, 1 H; 7.77 m, 2 H; 7.98 d, 2 H; 8.06 d, 1 H
3.88 s, 3 H (CH3O); 7.14 d, 2 H; 7.52–7.60 m, 3 H; 7.78 q, 2 H; 8.05 d, 1 H
2g
1.42 t, 3 H (CH3); 4.15 q, 2 H (CH2O); 7.12 d, 2 H; 7.53–7.57 m, 3 H;
7.76 q, 2 H; 8.05 d, 1 H
2h
2i
1H
1H
1H
2.70 s, 3 H (CH3CO); 7.56 m, 1 H; 7.79 q, 2 H; 7.86 d, 2 H; 8.08 d, 1 H; 8.18 d, 2 H
7.57 m, 1 H; 7.80 q, 2 H; 8.03 d, 2 H; 8.09 d, 1 H; 8.48 d, 2 H
3a
6.89–6.94 m, 2 H; 7.30–7.37 m, 2 H; 7.43 t, 1 H; 7.50–7.55 m, 2 H;
7.59–7.62 m, 2 H; 9.70 s, 1 H (OH); 12.45 s, 1 H (NH)
3b
3c
1H
1H
2.39 s, 3 H (CH3); 6.88–6.94 m, 2 H; 7.31–7.35 m, 4 H; 7.47 d, 2 H; 9.66 s,
1 H (OH); 12.41 s, 1 H (NH)
6.90–6.94 m, 2 H; 7.32–7.36 m, 2 H; 7.63–7.68 m, 4 H; 9.71 s, 1 H (OH);
12.48 s, 1 H (NH)
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

1760
Styskala, Slouka, Hejsek, Bekarek:
TABLE IV
(Continued)
Compound Nucleus
Chemical shifts
3d
3e
3f
1H
1H
1H
1H
1H
1H
6.90–6.93 m, 2 H; 7.32–7.35 m, 2 H; 7.65 A2B2 pattern, 4 H (δA = 7.58,
δB = 7.72, J = 9 Hz); 9.71 s, 1 H (OH); 12.48 s, 1 H (NH)
6.90–6.93 m, 2 H; 7.33 t, 2 H; 7.43 d, 2 H; 7.88 d, 2 H; 9.68 s, 1 H (OH);
12.48 s, 1 H (NH)
3.83 s, 3 H (CH3O); 6.88–6.93 m, 2 H; 7.06 d, 2 H; 7.34 q, 2 H;
7.50 d, 2 H; 9.74 s, 1 H (OH); 12.39 s, 1 H (NH)
3g
3h
3i
1.38 t, 3 H (CH3); 4.10 q, 2 H (CH2O); 6.87–6.92 m, 2 H; 7.04 d, 2 H;
7.34 q, 2 H; 7.47 d, 2 H; 9.79 s, 1 H (OH); 12.36 s, 1 H (NH)
2.65 s, 3 H (CH3CO); 6.92–6.95 m, 2 H; 7.36 q, 2 H; 7.79 d, 2 H;
8.10 d, 2 H; 9.77 s, 1 H (OH); 12.50 s, 1 H (NH)
6.92 t, 2 H; 7.36 q, 2 H; 7.96 d, 2 H; 8.39 d, 2 H; 9.87 s, 1 H (OH);
12.59 s, 1 H (NH)
a Measured in CDCl3.
Compounds 2 are derivatives of a new heterocyclic system. They are yellow crystal-
line substances, insoluble in water, well soluble in organic solvents, which exhibit yel-
low-green fluorescence at 366 nm. In the mass spectrum of compound 2a, distinct
peaks of molecular ion m/z 263.3 and of a fragment C9H4N3O2 (m/z 186.2) were ob-
served which arose by splitting of phenyl from 2a. The stability of compounds 2 to-
wards hydrolytic splitting might be of interest. Contrary to 1,2,4-triazine analogues
which contain fused isocoumarin ring17, compounds 2 are very susceptible to hydro-
lytic splitting. The hydrolysis takes place slowly already during standing of a solution
of these compounds in aqueous ethanol at room temperature. That is why we preferred
TABLE V
The mass spectra of compounds 1a, 2a and 3a
Compound
m/z (relative abundance, %)
1a
2a
3a
309.3 (100, M+), 263.3 (68, C15H9N3O2+), 91.1 (51, C6H5N+), 77.1 (100, C6H+5)
263.3 (100, M+), 186.2 (61, C9H4N3O+2), 77.1 (41, C6H+5)
281.3 (90, M+), 210.3 (38, C13H10N2O+), 91.1 (100, C6H5N+)
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

Synthesis of Arylbenzofurotriazines
1761
measuring UV spectra of compounds 2a–2i in benzene. Contrary to analogues deriva-
tives of pyrazolo[3,4-e][1,2,4]triazine9 or 1,2,4-triazino[4,5-a]benzimidazole18, the tria-
zine ring in compounds 2 is stable, hydrolytic splitting thus gave corresponding
1-aryl-5-(2-hydroxyphenyl)-6-azauracils 3a–3i (Scheme 1). In the mass spectrum of
compound 3a, both molecular ion peak m/z 281.3 and the peak of fragment C13H10N2O
(m/z 210.3) were observed, which probably arose by partial destruction of 1,2,4-triazine
ring, and also the peak of fragment C6H5N (m/z 91.1) mentioned above.
EXPERIMENTAL
The melting points were determined on a Boetius stage and are uncorrected. The infrared spectra
were measured in KBr disks and scanned on an ATI Unicam Genesis FTIR instrument. Electronic
absorption spectra were measured on a UV-VIS PU 8700 spectrophotometer (Philips) in ethanol
(compounds 1 and 3) and in benzene (compound 2), concentration 5.0 . 10–5 mol dm–3. The NMR
spectra were measured in (CD3)2SO on a Bruker AMX-360 spectrometer (360 MHz); the chemical
shifts are reported in ppm. Elemental analyses were performed with an EA 1108 Elemental Analyser
(Fison Instrument). Mass spectra were measured on a ZAB-SEQ mass spectrometer (VG Organic,
Manchester, U.K.) using electron impact (EI) ionization. The characteristic data of compounds 1–3
are given in Tables I–III, their NMR spectra in Table IV, and mass spectra of compounds 1a–3a in
Table V.
Ethyl N-(3-Arylhydrazono-2,3-dihydrobenzo[b]furan-2-ylidene)carbamates 1a–1i. General Procedure
A solution of corresponding aromatic amine (6.00 mmol) in a mixture of ice water (30 ml) and 37%
hydrochloric acid (3.6 ml) was diazotized with a solution of sodium nitrite (6.00 mmol) in ice water
(10 ml). The mixture was stirred in ice bath for 15 min and then added portionwise to a solution of
ethyl N-(benzo[b]furan-2-yl)carbamate19 (6.04 mmol) in pyridine (60 ml), which was cooled to 0–5 °C.
The mixture was left to stand at 0–5 °C for 24 h and then slowly diluted with ice water to total
volume of 900 ml. The next day the precipitated pale orange solid was collected by suction, washed
with water, dried, and for analysis recrystallized from ethanol. For further details, see Tables I, IV
and V.
2-Aryl[1]benzofuro[2,3-e][1,2,4]triazin-3(2H)-ones 2a–2i. General Procedure
A solution of corresponding hydrazonocarbamate 1 (4.00 mmol) in boiling decalin (40 ml) was re-
fluxed for 1 h and then cooled. After several hours, a yellow solid was collected by suction, washed
with hexane and dried at 110 °C in vacuum. Sample for analysis was obtained by recrystallization
from benzene. For further details, see Tables II, IV and V.
2-Aryl-6-(2-hydroxyphenyl)-1,2,4-triazine-3(2H),5(4H)-diones 3a–3i. General Procedure
A solution of a compound 2 (0.2 mmol) in a mixture of pyridine (10 ml) and water (10 ml) was
refluxed for 1 h and then evaporated to dryness. The residue was mixed with water (5 ml), collected
by suction, washed with water and dried. Sample for analysis was obtained by recrystallization from
ethanol. For further details, see Tables III–V.
Collect. Czech. Chem. Commun. (Vol. 62) (1997)

1762
Styskala, Slouka, Hejsek, Bekarek:
REFERENCES
1. Stejskalova E., Slouka J.: Acta Univ. Palacki. Olomuc., Fac. Rerum Nat. 102, 145 (1991).
2. Slouka J., Sramkova M., Bekarek V.: Collect. Czech. Chem. Commun. 42, 3449 (1977).
3. Slouka J., Bekarek V.: Collect. Czech. Chem. Commun. 45, 1379 (1980).
4. Slouka J., Nalepa K.: Z. Chem. 26, 134 (1986).
5. Slouka J.: Pharmazie 43, 413 (1977).
6. Slouka J.: Pharmazie 43, 864 (1988).
7. Slouka J., Cesalova M.: Acta Univ. Palacki. Olomuc., Fac. Rerum Nat. 69, 107 (1981).
8. Slouka J., Pec P.: Monatsh. Chem. 103, 1444 (1972).
9. Slouka J., Bekarek V., Pec P.: Acta Univ. Palacki. Olomuc., Fac. Rerum Nat. 49, 227 (1976).
10. Slouka J.: Tetrahedron Lett. 9, 4007 (1968).
11. Slouka J.: Monatsh. Chem. 100, 91 (1969).
12. Slouka J., Pec P., Urbanova J.: Acta Univ. Palacki. Olomuc., Fac. Rerum Nat. 37, 481 (1972).
13. Slouka J., Bekarek V.: Collect. Czech. Chem. Commun. 49, 275 (1984).
14. Pec P., Slouka J.: Chem. Zvesti 29, 418 (1975).
15. Slouka J., Bekarek V., Stemberk V.: Collect. Czech. Chem. Commun. 43, 960 (1978).
16. Slouka J.: Acta Univ. Palacki. Olomuc., Fac. Rerum Nat. 61/65, 111 (1979/80).
17. Hejsek M., Slouka J., Bekarek V.: Collect. Czech. Chem. Commun. 57, 123 (1992).
18. Slouka J., Budikova M.: Acta Univ. Palacki. Olomuc., Fac. Rerum. Nat. 45, 113 (1974).
19. Stoermer R., Calov G.: Ber. Dtsch. Chem. Ges. 34, 770 (1901).
Collect. Czech. Chem. Commun. (Vol. 62) (1997)