Indoles from 3-nitropyridinium salts: An extension of the transformation method on 5-substituted indoles

Article abstract of DOI:10.1016/S0040-4020(00)01162-5

The method of indole preparation by transformation of 3-nitropyridinium salts was successfully extended to the synthesis of indoles containing substituents Cl, PhS, CN, Ac and COOEt on the 5-position.

Full text of DOI:10.1016/S0040-4020(00)01162-5

TETRAHEDRON
Pergamon
Tetrahedron 57 (2001) 1827±1831
Indoles from 3-nitropyridinium salts:q an extension of the
transformation method on 5-substituted indoles
Oleg D. Mitkin, Roman V. Kombarov and Marina A. Yurovskayap
Department of Chemistry, M.V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation
Received 29 August 2000; revised 29 November 2000; accepted 14 December 2000
AbstractÐThe method of indole preparation by transformation of 3-nitropyridinium salts was successfully extended to the synthesis of
indoles containing substituents Cl, PhS, CN, Ac and COOEt on the 5-position. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
2. Results and discussion
The transformation of 3-nitropyridinium salts into indoles is
a rather new approach to prepare the indole skeleton. A
detailed scheme of this process was discussed before.2
The synthesis of 5-substituted 3-nitropyridines was carried
out by the reported method3 shown in Scheme 2 and Table 1.
Chromium trioxide in acetic acid was used as an oxidizing
agent to convert dihydropyridines 3a±i into corresponding
pyridines 4a±i. This reagent allowed the aromatisation to
proceed with facility and the pyridines were obtained in
high yields (70±90%). It is of interest to note that oxidation
of 4-furyl-substituted dihydropyridine 3h resulted not only
in the expected furyl pyridine but in the formation of a
signi®cant amount of defurylated pyridine as well
(Scheme 3).
This method was previously shown to be suitable for poly-
alkylindole and 4-phenylsubstituted indole preparation. We
have tried to expand this reaction in order to obtain indoles
substituted by other groups with different electronic
properties.
As shown in Scheme 1, the substituent in the 5-position of
3-nitropyridinium salt remains unchanged in the indole
system obtained. Besides, the 5-position is not subjected to
nucleophilic attack. Thus, there are only steric and electronic
effects which could in¯uence 4,6-meta-bridging of the pyri-
dine moiety by ketimine to give the ®nal indole bicycle.
Good results were achieved in quaternisation of substituted
nitropyridines with methyl tri¯uoromethanesulfonate. Such
reagents as Me2SO4 and MeI proved to be ineffective owing
to the low nucleophilicity of pyridine due to the presence of
two electron withdrawing groups. In the case of XˆCl, SPh
the reaction were carried out in re¯uxing dichloroethane.
The presence of such acceptor groups as CN, Ac, COOEt
in the 5-position did not allow completion of the reaction
under the same conditions. In these cases the quaternisation
was carried out at 1008C in sealed tubes.
We have used different 5-substituted 4-aryl-2,6-dimethyl-3-
nitropyridinium salts for their transformation into appro-
priate indoles. Such a series could favour higher yields of
4-phenylindoles and, moreover, the availability of
initial reagents allowed us to vary aryl substituents at the 4-
position and to analyse their in¯uence upon the process.
Scheme 1.
q Part 12.1
Keywords: pyridines; pyridinium salts; indoles; indolisation.
Corresponding author; e-mail: yumar@org.chem.msu.su
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)01162-5

1828
O. D. Mitkin et al. / Tetrahedron 57 (2001) 1827±1831
Scheme 2.
The indolisation procedure of nitropyridinium salts consists
in their treatment with excess of N-alkylketimine in DMF2
(Scheme 4).
Table 1. 5-Substituted 4-aryl-3-nitropyridines 4a±j
1,3,4
X
Ar
Yield (%) of 4
a
b
c
d
e
f
g
h
i
Cl
SPh
CN
Ac
COOEt
COOEt
COOEt
COOEt
COOEt
Ph
Ph
Ph
86
85
89
75
82
88
98
55
94
High yields of the indoles were obtained in the case of
XˆCl, SPh (salts 5a±b). But in the case of XˆCN, Ac,
CO2Et only trace amounts of the indoles were detected
while the isomeric nitroanilines were the major products
(Scheme 5).
3-NO2C6H4
2-CF3C6H4
4-BrC6H4
3,4-(MeO)2C6H3
2-Furyl
2-Thienyl
The process in Scheme 5 is analogous to the known
rearrangement of the pyridinium salts under the action of
bases4 (Scheme 6).
Scheme 3.
The presence of an additional electron withdrawing group in
the salts 5 increases the acidity of the 2- and 6-methyl
groups in such a manner that N-methylketimine could act
as a base converting pyridinium salt into intermediate
anhydrobase which could lead to the recyclisation process
forming the anilines. Moreover, as we have shown
previously,5 anhydrobases are not intermediates in the
3-nitropyridinium salts transformation into indoles. By
using acetic acid we managed to suppress this redundant
acidic±basic process and to make the indolisation pathway
predominant (Scheme 7, Table 2).
Scheme 4.
Scheme 5.
Good yields of indoles 6a±I were achieved from the salts
with XˆCN, CO2Et (5c,f±i). In the case of XˆAc the yields
were mediocre and the amount of by-products increased as a
probable result of acyl group condensation.
Variation of aryl substituent in the 4-position did not
in¯uence signi®cantly the process except for the case of
the salt 5e with strongly electron withdrawing 2-CF3C6H4
group which produced consistent low yields of indole. In this
case, furan 7 was detected by chromato-mass spectrometry
Scheme 6.

O. D. Mitkin et al. / Tetrahedron 57 (2001) 1827±1831
1829
Scheme 7.
of NMR spectra completely correspond to proposed
structures.
Table 2. Yield of pyridinium salts and indoles
4,5,6
X
Ar
Yield (%) of 5 Yield (%) of 6
4.2. Oxidation of dihydropyridines 3a±j to pyridines
4a±j
A
B
C
D
E
F
G
H
I
Cl
SPh
CN
Ac
COOEt
COOEt
COOEt
COOEt
COOEt
Ph
Ph
Ph
96
80
79
89
76
81
94
77
68
51
64
42
15
10
88
92
61
68
Chromium trioxide (1.5 mmol) was dissolved in the
minimum quantity of water and acetic acid (3 mL) was
added. The resulting solution was added to a stirred mixture
of dihydropyridine 3a±j (1.0 mmol) and acetic acid
(10 mL). The mixture was stirred and heated gradually to
about 60±1008C until dihydropyridine had disappeared
(TLC), then diluted with water (50 mL), and extracted
3-NO2C6H4
2-CF3C6H4
4-BrC6H4
3,4-(MeO)2C6H3
2-Furyl
2-Thienyl
Scheme 8.
as a by-product of the reaction. Formation of such
unexpected product presumably resulted from opening of
the pyridinium ring, followed by deacylation and
subsequent oxidative cyclisation (Scheme 8).
with toluene (3£20 mL). The organic layer was washed
with water, dried (Na2SO4), ®ltered through a thin layer of
silica gel and evaporated in vacuo.
1
4a. White powder, mp 96±988C from hexane; H NMR: d
7.22±7.50 (m, 5H, aromatic), 2.95 (s, 3H, 2-CH3), 2.69 (s,
3H, 6-CH3). Anal. Calcd for C13H11ClN2O2: C, 59.44; H,
4.22; N, 10.66. Found: C, 59.38; H, 4.27; N, 10.49.
3. Conclusions
Thus the process of transformation of 3-nitropyridinium
salts, obtaining indoles was expended to allow some func-
tional groups in the 5-position. Such a process proved to
depend on the acidity of the reaction conditions in most
cases.
1
4b. White powder, mp 104±1058C from hexane; H NMR:
d 6.91±7.40 (m, 10H, aromatic), 2.61 (s, 3H, 2-CH3), 2.55
(s, 3H, 6-CH3). Anal. Calcd for C19H16N2O2S: C, 67.84; H,
4.79; N, 8.33. Found: C, 67.28; H, 4.69; N, 7.85.
4c. White powder, mp 125±1268C from hexane; 1H NMR: d
7.36±7.56 (m, 5H, aromatic), 2.81 (s, 3H, 2-CH3), 2.61 (s,
3H, 6-CH3). Anal. Calcd for C14H11N3O2: C, 66.40; H, 4.38;
N, 16.59. Found: C, 66.22; H, 4.26; N, 16.59.
4. Experimental
4.1. General
4d. White powder, mp 127±1288C from EtOH; 1H NMR: d
7.68±8.39 (m, 4H, aromatic), 2.60 (s, 3H, 2-CH3), 2.56 (s,
3H, 6-CH3), 2.13 (s, 3H, CH3CO). Anal. Calcd for
C15H13N3O5: C, 57.14; H, 4.16; N, 13.33. Found: C,
57.52; H, 3.93; N, 13.36.
1
Melting points are uncorrected. All H NMR spectra were
recorded on Bruker AC-200 NMR spectrometer in DMSO-
d6 or in CDCl3. Mass spectra were recorded on a Finnigan
MAT-90 mass spectrometer at an ionizing voltage 70 eV.
Compounds 3a±l were prepared according to literature
procedure.6 Unfortunately, in some cases (salts 5e,f,h,i)
we could not select suitable solvents for their crystallisation,
so the data of elementary analysis are not given, but the data
1
4e. White powder, mp 68±698C from hexane; H NMR: d
7.28±7.81 (m, 4H, aromatic), 3.97 (q, Jˆ7 Hz, 2H,
CH2CH3), 2.67 (s, 3H, 2-CH3), 2.62 (s, 3H, 6-CH3), 0.87

1830
O. D. Mitkin et al. / Tetrahedron 57 (2001) 1827±1831
(t, Jˆ7 Hz, 3H, CH2CH3). Anal. Calcd for C17H15F3N2O4:
C, 55.44; H, 4.10; N, 7.61. Found: C, 55.23; H, 4.03; N,
7.49.
1-CH3), 4.09 (d q, Jˆ7, 2 Hz, 2H, CH2CH3), 2.96 (s, 3H, 2-
CH3), 2.90 (s, 3H, 6-CH3), 0.91 (t, Jˆ7 Hz, 3H, CH2CH3).
5f. White plats, mp 143±1458C; 1H NMR: d 7.27 and 7.84
(AA0BB0, 4H, aromatic), 4.26 (s, 3H, 1-CH3), 4.17 (q,
Jˆ7 Hz, 2H, CH2CH3), 3.31 (s, 3H, 2-CH3), 2.91 (s, 3H,
6-CH3), 0.98 (t, Jˆ7 Hz, 3H, CH2CH3).
5g. White plats, mp 202±2038C; 1H NMR: d 6.81±7.19 (m,
3H, aromatic), 4.23 (s, 3H, 1-CH3), 4.19 (q, Jˆ7 Hz, 2H,
CH2CH3), 3.75 and 3.85 (2s, 6H, 2£OCH3), 2.88 (s, 3H; 2-
CH3), 2.83 (s, 3H, 6-CH3), 1.00 (t, Jˆ7 Hz, 3H, CH2CH3).
Anal. Calcd for C20H23F3N2O9S: C, 45.80; H, 4.42; N, 5.34.
Found: C, 46.08; H, 4.45; N, 5.16.
4f. White powder, mp 102±1038C from hexane; 1H NMR: d
7.20 and 7.69 (AA0BB0, 4H, aromatic), 4.05 (q, Jˆ7 Hz,
2H, CH2CH3), 2.58 (s, 3H, 2-CH3), 2.55 (s, 3H, 6-CH3),
0.94 (t, Jˆ7 Hz, 3H, CH2CH3). Anal. Calcd for
C16H15BrN2O4: C, 50.68; H, 3.99; N, 7.39. Found: C,
50.40; H, 3.84; N, 7.21.
4g. White powder, mp 121±1238C from hexane; 1H NMR: d
6.73±7.01 (m, 3H, aromatic), 4.07 (q, Jˆ7 Hz, 2H,
CH2CH3), 3.77 and 3.84 (2s, 6H, 2£OCH3), 2.56 (s, 3H,
2-CH3), 2.52 (s, 3H, 6-CH3), 1.00 (t, Jˆ7 Hz, 3H,
CH2CH3). Anal. Calcd for C18H20N2O6: C, 60.00; H, 5.56;
N, 7.78. Found: C, 60.17; H, 5.66; N, 7.66.
1
5h. White plats, mp 115±1188C; H NMR; d 6.86, 7.15,
8.16 (m, 3H, aromatic), 4.48 (q, Jˆ7 Hz, 2H, CH2CH3),
4.17 (s, 3H, 1-CH3), 2.83 (s, 3H, 2-CH3), 2.78 (s, 3H, 6-
CH3), 1.32 (t, Jˆ7 Hz, 3H, CH2CH3).
1
4h. White powder, mp 73±758C from hexane; H NMR: d
6.52, 7.25, 7.55 (m, 3H, aromatic), 4.33 (q, Jˆ7 Hz, 2H,
CH2CH3), 2.62 (s, 3H, 2-CH3), 2.57 (s, 3H, 6-CH3), 1.27 (t,
Jˆ7 Hz, 3H, CH2CH3). Anal. Calcd for C14H14N2O5: C,
57.93; H, 4.86; N, 9.65. Found: C, 58.10; H, 4.81; N, 9.43.
1
5i. H NMR: d 7.31 and 8.09 (m, 3H, aromatic), 4.28 (q,
Jˆ7 Hz, 2H, CH2CH3), 4.22 (s, 3H, 1-CH3), 2.87 (s, 3H, 2-
CH3), 2.83 (s, 3H, 6-CH3), 1.00 (t, Jˆ7 Hz, 3H, CH2CH3).
1
4i. White powder, mp 69±708C from hexane; H NMR: d
4.4. Reaction of salt 5d with N-methylacetoneimine
7.07±7.50 (m, 3H, aromatic), 4.17 (q, Jˆ7 Hz, 2H,
CH2CH3), 2.64 (s, 3H, 2-CH3), 2.60 (s, 3H, 6-CH3), 1.10
(t, Jˆ7 Hz, 3H, CH2CH3). Anal. Calcd for C14H14N2O4S: C,
54.89; H, 4.61; N, 9.14. Found: C, 54.99; H, 4.37; N, 9.13.
N-Methylacetonimine (5 mmol) was added to solution of 5d
(1 mmol) in DMF (5 mL). The reaction mixture was
allowed to stand for 4 days then diluted with water
(50 mL), extracted with toluene (2£15 mL), washed with
water (3£20 mL), dried (Na2SO4) and evaporated in
vacuo. The residue was ¯ash chromatographed on silica
gel (Merck 0.015±0.040 mm) using at ®rst pure toluene
then suitable ratio of EtOAc/toluene (1:9, 2:9, 1:3) as eluent.
4.3. Preparation of 1-methylpyridinium tri¯uoro-
methanesulfonates
A solution of 3-nitropyridine 4a±i (1 mmol) and methyl
tri¯uoromethanesulfonate (1.3 mmol) in dichloroethane
(5 mL) was re¯uxed (in the case of 4a,b) or heated at
108C in a sealed tube (in the case of 4c±i) for 30 h. After
cooling and evaporation in vacuo the residue was treated
with diethyl ether and the salt was collected by ®ltration.
4.4.1. 4-Acetyl-6-methyl-2-nitro-3-(3-nitrophenyl)-N-
methylaniline. Yield 10%, orange solid, mp 1448C from
1
toluene; H NMR: d 7.60±8.27 (m, 4H, aromatic), 6.81 (s,
1H, 5-H), 6.78 (m, 1H, NH), 2.94 (d, Jˆ4.4 Hz, 3H, NCH3),
2.29 (s, 3H, 6-CH3), 1.85 (s, 3H, CH3CO); m/z (%): 329(M1,
59), 314 (100). Anal. Calcd for C16H15N3O5: C, 58.36; H,
4.56; N, 12.77. Found: C, 58.10; H, 4.30; N, 12.58.
5a. White plats, mp 192±1938C; 1H NMR: d 7.31±7.61 (m,
5H, aromatic), 4.32 (s, 3H, 1-CH3), 3.08 (s, 3H, 2-CH3),
2.83 (s, 3H, 6-CH3). Anal. Calcd for C15H14ClF3N2O5S: C,
42.21; H, 3.31; N, 6.56. Found: C, 42.06; H, 3.03; N, 6.23.
4.4.2. 2-Acetyl-6-methyl-4-nitro-3-(3-nitrophenyl)-N-
methylaniline. Yield 2%, pale yellow solid, mp 1838C
5b. White plats, mp 121±1238C; 1H NMR: d 7.01±7.52 (m,
10H, aromatic), 4.29 (s, 3H, 1-CH3), 3.07 (s, 3H, 2-CH3),
2.86 (s, 3H, 6-CH3). Anal. Calcd for C21H19F3N2O5S2: C,
50.40; H, 3.83; N, 5.60. Found: C, 50.25; H, 3.75; N, 5.80.
1
from EtOH; H NMR: d 7.64±8.34 (m, 4H, aromatic),
7.01 (s 1H, NH), 6.60 (s, 1H, 5-H), 2.94 (s, 3H, NCH3),
2.40 (s, 3H, 6-CH3), 1.65 (s, 3H, CH3CO); m/z (%): 329
(M1, 100), 314 (95).
1
5c. White plats, mp 232±2338C from MeCN/EtOAc; H
NMR: d 7.51±7.74 (m, 5H, aromatic), 4.34 (s, 3H,
1-CH3), 3.19 (s, 3H, 2-CH3), 2.96 (s, 3H, 6-CH3). Anal.
Calcd for C16H14F3N3O5S: C, 46.05; H, 3.38; N, 10.07.
Found: C, 45.92; H, 3.21; N, 10.22.
4.5. Indolisation of 5a±j
A solution of N-methylacetonimine (5 mmol) and acetic
acid (10 mmol, not required in the cases of 5a,b) was
added to solution of 5a±j (1 mmol), in DMF (5 mL), in
the case of 5h the quantities of all reagents were decreased
10 times. The reaction mixture was allowed to stand for
5 days then diluted with water (50 mL), extracted with
toluene (2£15 mL), washed with water (5£20 mL), dried
(Na2SO4), ®ltered through thin layer of silica gel and evapo-
rated in vacuo. For all indoles obtained with low yields
(6d,e) and in the case of microquantities of reagents (5h)
5d. White plats, mp 213±2148C; 1H NMR: d 7.76±8.19 (m,
4H, aromatic), 4.30 (s, 3H, 1-CH3), 2.89 (s, 3H, 2-CH3),
2.86 (s, 3H, 6-CH3), 2.25 (s, 3H, CH3CO). Anal. Calcd for
C17H16F3N3O8S: C, 42.59; H, 3.34; N, 8.77. Found: C,
42.31; H, 3.29; N, 8.82.
1
5e. H NMR: d 7.33±7.89 (m, 4H, aromatic), 4.31 (s, 3H,

O. D. Mitkin et al. / Tetrahedron 57 (2001) 1827±1831
1831
1
only the data of mass-spectrometry and NMR spectroscopy
are reported.
6g. White needles, mp 106±1078C from hexane; H NMR:
d 6.86 and 7.23 (m, 4H, aromatic), 6.02 (s, 1H, 3-H), 4.00
(q, Jˆ7 Hz, 2H, CH2CH3), 3.75 and 3.81 (2s, 6H, 2£OCH3),
3.67 (s, 3H, 1-CH3), 2.41 (s, 3H, 6-CH3), 2.37 (s, 3H, 2-
CH3), 0.97 (t, Jˆ7 Hz, 3H, CH2CH3). Anal. Calcd for
C22H25NO4: C, 71.91; H, 6.86; N, 3.81. Found: C, 71.67;
H, 6.80; N, 3.66.
1
6a. White needles, mp 112±1138C from hexane; H NMR:
d 7.48±7.50 (m, 5H, aromatic), 7.13 (s, 1H, 7-H), 5.91 (s,
1H, 3-H), 3.66 (s, 3H, 1-CH3), 2.58 (s, 3H, 6-CH3), 2.37 (s,
3H, 2-CH3). Anal. Calcd for C17H16ClN: C, 75.69; H, 5.98;
N, 5.19. Found: C, 75.97; H, 5.78; N, 5.00.
6h. Oil; 1H NMR: d 6.42, 6.62, 7.28, 7.72 (m, 5H,
aromatic), 4.22 (q, Jˆ7 Hz, 2H, CH2CH3), 3.69 (s, 3H,
1-CH3), 2.43 (s, 3H, 6-CH3), 2.39 (s, 3H, 2-CH3), 1.18 (t,
Jˆ7 Hz, 3H, CH2CH3); m/z (%): 297(M1, 100), 269 (12),
268 (40), 252 (15), 240 (27), 224 (5).
1
6b. White needles, mp 166±1678C from hexane; H NMR:
d 6.88±7.32 (m, 11H, aromatic), 5.93 (s, 1H, 3-H), 3.71 (s,
3H, 1-CH3), 2.56 (s, 3H, 6-CH3), 2.38 (s, 3H, 2-CH3). Anal.
Calcd for C23H21NS: C, 80.43; H, 6.16; N, 4.08. Found: C,
80.78; H, 6.13; N, 3.98.
6i. White needles, mp 122±1238C from hexane; 1H NMR: d
7.05±7.61 (m, 4H, aromatic), 6.20 (s, 1H, 3-H), 4.08 (q,
Jˆ7 Hz, 2H, CH2CH3), 3.68 (s, 3H, 1-CH3), 2.39±2.40
(2s, 6H, 2,6-CH3), 1.06 (t, Jˆ7 Hz, 3H, CH2CH3). Anal.
Calcd for C18H19NO2S: C, 68.98; H, 6.11; N, 4.47. Found:
C, 69.37; H, 6.19; N, 4.14.
6c. White needles, mp 193±1958C from hexane: 1H NMR: d
7.50±7.56 (m, 5H, aromatic), 7.46 (s, 1H, 7-H), 6.06 (s, 1H,
3-H), 3.71 (s, 3H, 1-CH3), 2.62 (s, 3H, 6-CH3), 2.39 (s, 3H,
2-CH3). Anal. Calcd for C18H16N2: C, 83.07; H, 6.15; N,
10.77. Found: C, 82.96; H, 6.27; N, 10.73.
6d. White needles, mp 176±1778C from EtOH; 1H NMR: d
7.57±8.41 (m, 4H, aromatic), 7.16 (s, 1H, 7-H), 6.05 (s, 1H,
3-H), 3.71 (s, 3H, 1-CH3), 2.44 (s, 3H, 6-CH3), 2.42 (s, 3H,
2-CH3), 2.05 (s, 1H, CH3CO); m/z (%): 322(M1, 92), 307
(100).
References
1. For Part 11 see: Karchava, A. V.; Yurovskaya, M. A.; Wagner,
T. R.; Zybailov, B. L.; Bundel, Y. G. Tetrahedron: Asymmetry
1995, 6, 2895±2898.
6e. m/z (%): 375(M1, 100), 347 (7), 330 (22).
2. Yurovskaya, M. A.; Afanasyev, A. Z.; Maximova, F. V.;
Bundel, Yu. G. Tetrahedron 1993, 40, 4945±4954.
3. Stradin, J.; Gavars, R.; Baumane, L.; Vigante, B.; Dubur, G.
Khim. Geterotsikl. Soedin. 1993, 8, 1079±1087 (in Russian).
4. Sagitullin, R. S.; Gromov, S. P.; Kost, A. N. Dokl. Akad. Nauk
USSR 1977, 236, 634±636 (in Russian).
7. m/z (%): 343(M1, 100), 315 (11), 313 (4), 298 (19), 274
(41).
6f. White needles, mp 117±1188C from i-PrOH; 1H NMR: d
7.27 and 7.63 (AA0BB0, 4H, aromatic), 7.29 (s, 1H, 7-H),
5.94 (s, 1H, 3-H), 3.99 (q, Jˆ7 Hz, 2H, CH2CH3), 3.68
(s, 3H, 1-CH3), 2.43 (s, 3H, 6-CH3), 2.36 (s, 3H, 2-CH3),
0.95 (t, Jˆ7 Hz, 3H, CH2CH3). Anal. Calcd for
C20H20BrNO2: C, 62.17; H, 5.18; N, 3.63. Found: C,
62.10; H, 5.04; N, 7.64.
5. Yurovskaya, M. A.; Afanasyev, A. Z.; Chertkov, V. A.; Bundel,
Yu. G. Khim. Geterotsikl. Soedin. 1990, 9, 1214±1216 (in
Russian).
6. Bossert, F.; Franckoviak, G.; Heise, A.; Kazda, S.; Meyer, H.;
Stoepel, K.; Towart, R.; Wehinger, E. (Bayer, A.-G.) Ger. Offen
2,752,820. (Cl. C07D211/84); Chem. Abstr. 1979, 91, 107,898