A versatile synthesis of 4,5-dihydropyrrolo[1,2-a]quinoxalines

Article abstract of DOI:10.1002/jhet.5570380321

The reaction of 1-(2-aminophenyl)pyrrole with aromatic or heteroaromatic aldehydes in ethanol and catalytic amounts of acetic acid leads to 4,5-dihydropyrrolo[1,2-a]quinoxalines in high yields. When aliphatic aldehydes were used under the same conditions, a slow oxidation to the corresponding pyrrolo[1,2-a]quinoxalines can occur; the oxidation can be avoided by preparing in situ the 5-acetyl derivatives of the 4,5-dihydropyrrolo[1,2-a]quinoxalines.

Full text of DOI:10.1002/jhet.5570380321

May-Jun 2001
A Versatile Synthesis of 4,5-Dihydropyrrolo[1,2-a]quinoxalines
671
Rodrigo Abonia*, Braulio Insuasty and Jairo Quiroga
Departamento de Química, Universidad del Valle, A.A. 25360, Cali, Colombia
Heinz Kolshorn and Herbert Meier
Institute of Organic Chemistry, University of Mainz, Duesbergweg 10-14, D-55099 Mainz, Germany
Received October 2, 2000
The reaction of 1-(2-aminophenyl)pyrrole with aromatic or heteroaromatic aldehydes in ethanol and
catalytic amounts of acetic acid leads to 4,5-dihydropyrrolo[1,2-a]quinoxalines in high yields. When
aliphatic aldehydes were used under the same conditions, a slow oxidation to the corresponding
pyrrolo[1,2-a]quinoxalines can occur; the oxidation can be avoided by preparing in situ the 5-acetyl
derivatives of the 4,5-dihydropyrrolo[1,2-a]quinoxalines.
J. Heterocyclic Chem., 38, 671 (2001).
Pyrrolo[1,2-a]quinoxalines and their 4,5-dihydro
in ethanol were heated for 5 to 10 minutes at 50 °C in the
presence of catalytic amount of acetic acid, the products
5a-i were generated in excellent yields. Terephthalal-
dehyde (4j) reacts with two equivalents of 3 to give 84% of
1,4-bis(4,5-dihydropyrrolo[1,2-a]quinoxalin-4-yl)benzene
5j. Carbon atom C-4 in 5 is a chiral center. Therefore 5a-i
were obtained as racemates; however, compound 5j has
two chiral centers and should be generated in the chiral
form (RR and SS) and in the achiral meso form. Although
the two chiral centers are relatively far apart, some of the
derivatives exhibit interesting biological and pharma-
cological properties [1-6]. Particularly the compounds
1 proved to be useful materials for pharmaceutical
preparations [5]; the commercially available maleate of
compound 2 (CGS 12066B) is recognized as a potent and
selective serotonin-1B agonist [6].
13
C nmr signals are doubled, which is a proof for
diastereomers. The statistical ratio RR/SS: meso would be
13
1:1; however, the C nmr spectrum of the raw product
reveals that one component predominates strongly.
When aliphatic aldehydes like 4k and 4l were applied,
the products 5k and 5l showed a slow oxidation to the
corresponding pyrrolo[1,2-a]quinoxalines. The oxidation
could be avoided by the in situ subsequently performed
acetylation with acetic anhydride; thus, the amides 6k and
6l were obtained.
The mild reaction conditions (50 °C, catalytic amounts
of acetic acid) guaranteed a broad application of this
procedure. The only failure was observed when we used
2,4-dinitrobenzaldehyde (4m). A hardly soluble orange
Although the obtention of 4,5-dihydropyrrolo[1,2-a]-
quinoxalines from o-phenylenediamine and 2-hydroxy-
1,5-diketones has been previously reported [8], 1-(2-
aminophenyl)pyrrole (3) has been recognized as an
excellent precursor for the preparation of these and
related compounds [9-11]. However, the feasibility of
the latter method is strongly dependent on the carbonyl
compound and the reaction conditions. It has been
reported for example that the hydrochloride of
compound 3 in contrast to the free base does not react
with benzaldehyde [10].
The formation of 4,5-dihydropyrrolo[1,2-a]quinoxalines
involves a Mannich type reaction for which a primary or
secondary amine, an aldehyde (formaldehyde generally)
and a nucleophilic carbon are necessary. Besides
formaldehyde, other reactive aldehydes have been applied
in this process, some of them unsuccessfully [12,13]. For
that reason, we tried to explore the scope and the limita-
tions of this reaction starting from 1-(2-aminophenyl)-
pyrrole (3), which serves simultaneously as amine and
nucleophilic carbon. When 3 and aldehydes 4a-i dissolved
1
13
Figure 1. H and C nmr data of 5d in deuteriochloroform (chemical
shifts δ related to TMS as internal standard; the arrows indicate the most
important nuclear Overhauser effects).

672
R. Abonia, B. Insuasty, J. Quiroga, H. Kolshorn and H. Meier
Vol. 38
product precipitated immediately. It turned out that the
primarily formed Schiff base 7 does not undergo
cyclization, even when subjected to higher temperatures
and longer reaction times.
13
and C signals for 5d are shown in Figure 1. The various
substituents on C-4 have only a small influence on the
chemical shifts of the tricyclic scaffold.
The mass spectra of compounds 5 showed that the
molecular ions M are preferentially cleaved to [M – R]
EXPERIMENTAL
+•
+
where R represents the substituent on C-4; additionally the
The melting points were determined on a Kofler apparatus and
acetyl groups in 6k,l are split off, so that the ion
1
13
are uncorrected. The H and C nmr spectra were recorded with
Varian Gemini 200 and Bruker AM 400 instruments; chemical
shifts (δ) are reported in ppm relative to tetramethylsilane as
+
[C H N ] with m/z = 169 is formed in all cases 5a-j and
11
9 2
6k,l. The compounds were extensively characterized by
1
13
internal standard. Silica gel plates (Merck F ) were used for
their H and C nmr spectra including 2D-techniques like
254
1
analytical tlc. The mass spectra were run on a Varian Model MAT
MS-311 spectrometer at 70 eV. Microanalyses were performed
with a Perkin Elmer Model 240 C Elemental Analyser.
COSY, HMBC, NOESY [14]. The assignments of the H
General Procedure for the Preparation of the 4,5-Dihydro-
propyrrolo[1,2-a]quinoxalines 5a-l.
A solution of 1-(2-aminophenyl)pyrrole 3 (0.20 g,
1.26 mmoles) and the corresponding aldehyde 4 (1.26 mmoles of
4a-i,k,l and 0.63 mmoles of 4j), in ethanol (2 ml) and acetic acid
(5 drops) was heated to 50 °C during 5 to 10 minutes, following
the reaction by tlc on silica gel plates with chloroform as the

May-Jun 2001
A Versatile Synthesis of 4,5-Dihydropyrrolo[1,2-a]quinoxalines
673
eluent. After cooling, the resulting precipitate of 5a-i was filtered
off and recrystallized from ethanol. As soon as the starting
compounds for 5k,l were consumed, 194 mg (1.9 mmoles) of
acetic anhydride was added, and the reaction mixture was heated
at 50 °C for 2 minutes more. The solvent was removed under
Anal. Calcd for C H N O : C, 71.41; H, 5.99; N, 8.33.
20 20 2 2
Found: C, 71.37; H, 5.99; N, 8.26.
4-(3,5-Dichloro-2-hydroxyphenyl)-4,5-dihydropyrrolo[1,2-a]-
quinoxaline (5e).
3
reduced pressure (1.5 x 10 Pa) and the residue was purified by
This compound was obtained from 3,5-dichloro-2-hydroxy-
column chromatography (3 x 20 cm silica gel, chloroform).
4,5-Dihydro-4-phenylpyrrolo[1,2-a]quinoxaline (5a).
The compound was obtained from benzaldehyde (4a) as
benzaldehyde (4e) as pale yellow crystals in 96% yield, mp
1
194-195 °C. The H nmr spectrum in dimethyl sulfoxide-d
6
3
showed signals at δ 5.72 (d, J = 2.9 Hz, 1H, 3-H), 5.91 (s, 1H,
3
4-H), 6.19 (t, 1H, J = 2.9 Hz), 6.51 (br s, 1H, N-H), 6.74 (td, 1H,
1
colorless crystals in 94% yield, mp 90-91 °C. The H nmr spectrum
8-H), 6.86-6.94 (m, 2H, 6-H and 7-H), 7.01 (d, 1H, aryl),
in deuteriochloroform showed signals at δ 4.13 (br s, 1H, N-H),
13
7.42-7.46 (m, 2H, 1-H and aryl), 7.52 (d, 1H, 9-H); C nmr
3
4
5.53 (s, 1H, 4-H), 5.60 (dd, J = 2.9 Hz, J = 1.5 Hz, 1H, 3-H), 6.26
(hexadeuteriodimethyl sulfoxide): δ 48.5 (C-4), 105.2 (C-3),
110.0 (C-2), 114.6/ 114.8 (C-1, C-9), 115.2 (C-6), 118.2 (C-8),
121.9/ 123.2/ 124.1/ 124.8/ 126.0/ 126.9/ 127.7/ 135.9/ 149.1
3
(t, 1H, 2-H, J = 3.0 Hz), 6.73 (dd, 1H, 6-H), 6.86 (td, 1H, 8-H),
6.98 (td, 1 H, 7-H), 7.20 (dd, J = 3.0 Hz, J = 1.5 Hz, 1H, 1-H),
7.32-7.46 ppm (m, 6H, 9-H and phenyl protons); C nmr (deuterio-
3
4
13
(C-3a, C-7, C-9a and aryl-C), 133.8 (C-5a); ms: m/z (%) 330 (7)
chloroform): δ = 56.2 (C-4), 106.0 (C-3), 110.2 (C-2), 114.4 (C-1),
114.8 (C-9), 115.5 (C-6), 119.5 (C-8), 124.7 (C-7), 125.6 (C-9a),
+•
[M , Cl pattern], 169 (100).
2
Anal. Calcd for C H N OCl : C, 61.65; H, 3.65; N, 8.46.
17 12
2
2
127.8, 128.3, 128.7 (CH, Phenyl), 129.8 (C-3a), 136.0 (C-5a), 141.3
Found: C, 61.71; H, 3.71; N, 8.31.
+•
(C , Phenyl); ms: m/z (%) 246 (44) [M ], 169 (100).
i
4,5-Dihydro-4-(pentafluorophenyl)pyrrolo[1,2-a]quinoxalines
(5f).
Anal. Calcd. for C
Found: C, 82.86; H, 5.57; N, 11.36.
H N : C, 82.90; H, 5.73; N, 11.37.
17 14 2
This compound was obtained from pentafluorobenzaldehyde
(4f) as colorless crystals in 89% yield, mp 154-155 °C. The H
4,5-Dihydro-4-(4-trifluoromethoxyphenyl)pyrrolo[1,2-a]quinox-
aline (5b).
1
nmr spectrum in deuteriochloroform showed signals at δ 4.06
This compound was obtained from p-trifluoromethoxy-
benzaldehyde (4b) as colorless crystals in 81% yield, mp 80°.
3
(br s, 1H, N-H), 5.86 (br d, J = 3.4 Hz, 1H, 3-H), 6.26 (s, 1H,
3
4-H), 6.30 (t, J = 3.4 Hz, 1H, 2-H), 6.68 (dd, 1H, 6-H), 6.85
1
The H nmr spectrum in deuteriochloroform showed signals at δ
3
4
(td, 1H, 8-H), 6.97 (td, 1H, 7-H), 7.22 (dd, J = 3.0 Hz, J = 1.5
3
3
4.18 (br s, 1H, N-H), 5.54 (s, 1H, 4-H), 5.57 (dd, J = 3.4, J = 1.5
13
Hz, 1H, 1-H), 7.34 (dd, 1H, 9-H); C nmr (deuteriochloroform):
3
Hz, 1H, 3-H), 6.26 (t, J = 3.4 Hz, 1H, 2-H), 6.74 (dd, 1H, 6-H),
δ 45.8 (C-4), 105.6 (C-3), 110.1 (C-2), 114.4/ 114.6 (C-1, C-9),
115.1 (C-6), 119.6 (C-8), 124.8 (C-7), 126.4 (C-9a), 129.7
(C-3a), 133.8 (C-5a), 134.2-147.8 (aryl-C, superimposed); ms:
6.87 (td, 1H, 8-H), 6.99 (td, 1H, 7-H), 7.22 (m, 3H, 1-H and two
aromat. protons), 7.34 (dd, 1H, 9-H), 7.52 (br d, 2 H, aromat.
13
protons); C nmr (deuteriochloroform): δ 55.5 (C-4), 106.0
+•
m/z (%) 336 (35) [M ], 169 (100).
(C-3), 110.3 (C-2), 114.6/ 114.8 (C-1, C-9), 115.4 (C-6), 119.7
Anal. Calcd for C H N F : C, 60.72; H, 2.70; N, 8.33. Found:
1
17
9 2 5
(C-8), 120.5 (OCF , J = 384.2 Hz), 121.1/ 129.4 (CH, Aryl),
3
C, 60.75; H, 2.69; N, 8.33.
124.8 (C-7), 125.4 (C-9a), 129.4 (C-3a), 135.8 (C-5a), 140.2/
+•
149.1 (C , Aryl); ms: m/z (%) 330 (36) [M ], 169 (100).
q
4,5-Dihydro-4-(3-pyridyl)pyrrolo[1,2-a]quinoxaline (5g).
Anal. Calcd for C H N OF : C, 65.45; H, 3.97; N, 8.48.
18 13
2
3
This compound was obtained from 3-pyridinecarboxaldehyde
Found: C, 65.38; H, 3.79; N, 8.45.
1
(4g) as colorless crystals in 86% yield, mp 130-131 °C. The H
4-(2,3-Dihydroxyphenyl)-4,5-dihydropyrrolo[1,2-a]quinoxaline
(5c).
nmr spectrum in deuteriochloroform showed signals at δ 4.41 (br s,
3
1H, N-H), 5.56 (m, 2H, 3-H and 4-H), 6.24 (t, J = 2.9 Hz, 1H,
2-H), 6.76 (dd, 1H, 6-H), 6.85 (td, 1H, 8-H), 6.97 (td, 1H, 7-H),
This compound was obtained from 2,3-dihydroxybenzalde-
hyde (4c) as colorless crystals in 85% yield, mp 154-155 °C. The
3
4
7.19 (dd, J = 2.9 Hz, J = 1.5 Hz, 1H, 1-H), 7.24-7.34 (m, 2H, 9-H
and pyridine-H), 7.81 (dt, 1H, pyridine H), 8.56 (dd, 1H, pyri-
1
H nmr spectrum in deuteriochloroform showed signals at δ 5.52
13
dine H), 8.66 (d, 1H, pyridine-H); C nmr (deuteriochloroform): δ
3
4
(s, 1H, 4-H), 5.56 (dd, J = 3.4, J = 1.5 Hz, 1H, 3-H), 6.03 (br s,
3
53.9 (C-4), 106.1 (C-3), 110.3 (C-2), 114.6/ 114.8 (C-1, C-9), 115.5
(C-6), 119.8 (C-8), 123.8/ 135.7/ 137.1/ 149.4/ 149.8/ (pyridine C),
124.8 (C-7), 125.4 (C-9a), 128.8 (C-3a), 135.6 (C-5a); ms: m/z (%)
1H, N-H), 6.24 (t, J = 3.4 Hz, 1H, 2-H), 6.69 (dd, 1H, 6-H),
6.77-7.06 (m, 5H, 7-H, 8-H and aryl protons), 7.19 (m, 1H, 1-H),
13
7.35 (dd, 1H, 9-H); C nmr (deuteriochloroform): δ 56.3 (C-4),
+•
247 (34) [M ], 169 (100).
106.7 (C-3), 110.7 (C-2), 115.2/ 115.3/ 115.4 (C-1, C-6, C-9),
117.3, 120.7, 122.3 (CH, aryl), 120.1 (C-8), 122.9/ 143.4/ 145.6
Anal. Calcd for C H N : C, 77.71; H, 5.30; N, 16.99. Found:
16 13
3
77.68; H, 5.34; N, 17.04.
(C , aryl), 124.7 (C-7), 127.1 (C-9a), 128.1 (C-3a), 134.5 (C-5);
q
+•
ms: m/z (%) 278 (46) [M ], 169 (100).
4-(3-Chromonyl)-4,5-dihydropyrrolo[1,2-a]quinoxaline (5h).
This compound was obtained from 3-chromonaldehyde (4h) as
Anal. Calcd for C H N O : C, 73.37; H, 5.07; N, 10.07.
17 14
2 2
Found: C, 73.38; H, 5.13; N, 10.06.
1
yellow crystals in 86% yield, mp 172-173 °C. The H nmr
4,5-Dihydro-4-(3,4,5-trimethoxyphenyl)pyrrolo[1,2-a]quinoxa-
line (5d).
spectrum in deuteriochloroform showed signals at δ 5.28 (br s,
3
4
1H, N-H), 5.90 (s, 1H, 4-H), 6.10 (dd, J = 3.4 Hz, J = 1.5 Hz,
3
1H, 3-H), 6.37 (t, J = 3.4 Hz, 1H, 2-H), 6.67 (dd, 1H, 6-H), 6.77
This compound was obtained from 3,4,5-trimethoxybenzalde-
(td, 1H, 8-H), 6.88 (td, 1H, 7-H), 7.12 (s, 1H, CH-O), 7.25
(dd, J = 3.2 Hz, J = 1.5 Hz, 1H, 1-H), 7.28-7.42 (m, 3H, 9-H
and two aromatic H), 7.62 (td, 1H, aromatic H), 8.21 (dd, 1H,
hyde (4d) as colorless crystals in 96% yield, mp 127-128 °C. The
3
4
1
13
H nmr and the C nmr data are shown in Figure 1; ms: m/z (%)
+•
336 (31) [M ], 169 (100).

674
R. Abonia, B. Insuasty, J. Quiroga, H. Kolshorn and H. Meier
Vol. 38
13
3
3
aromatic H); C nmr (deuteriochloroform): δ 47.7 (C-4), 106.1
(C-3), 110.3 (C-2), 113.7/ 118.2/ 123.8/ 124.1/ 124.6/ 125.0/
125.2/ 125.7/ 133.9, 154.2, 156.4 (C-3a, C-7, C-9a and chrom.
C), 114.6/ 114.9 (C-1, C-9), 116.4 (C-6), 119.3 (C-8), 134.5
(s, 3H, COCH ), 5.95 (d, J = 7.3 Hz, 1H, 4-H), 6.03 (dd, J = 3.4
3
4
3
Hz, J = 1.0 Hz, 1H, 3-H), 6.27 (t, J = 3.4 Hz, 1H, 2-H), 7.11 (dd,
J = 2.9 Hz, J = 1.5 Hz, 1H, 1-H), 7.13-7.30 (m, 3H, 6-H, 7-H, 8-H),
7.39 (d, 1H, 9-H); C nmr (deuteriochloroform): δ 14.1 (CH ),
22.6/ 22.7/ 25.9/ 29.1/ 29.3/ 29.4/ 29.5/ 29.6/ 31.9/ 33.7 (CH ), 49.5
3
4
13
3
+•
(C-5a), 177.7 (C=O); ms: m/z (%) 314 (100) [M ], 169 (50).
2
Anal. Calcd for C
Found: C, 76.21; H, 4.55; N, 8.77.
H
N O : C, 76.42; H, 4.49; N, 8.91.
(C-4), 105.6 (C-3), 110.4 (C-2), 114.0/ 115.9 (C-1, C-9), 123.9 (C-7),
126.2 (C-6), 126.6 (C-8), 127.7 (C-9a), 129.7 (C-3a), 129.7 (C-5a),
169.2 (C=O); ms: m/z (%) 366 (23) [M ], 169 (100).
20 14
2 2
+•
4,5-Dihydro-4-styrylpyrrolo[1,2-a]quinoxaline (5i).
This compound was obtained from cinnamaldehyde (4i) as yellow
Anal. Calcd for C
H N O: C, 78.64; H, 9.35; N, 7.64.
24 34 2
Found: C, 78.39; H, 9.54; N, 7.74.
1
crystals in 87% yield, mp 125-126 °C. The H nmr spectrum in
N-[(E)-2,4-Dinitrophenylmethylidene]-2-(1H-pyrrol-1-yl)-
aniline (7).
deuteriochloroform showed signals at δ 4.07 (br s, 1H, N-H), 5.13
3
3
4
(d, J = 7.8 Hz, 1H, 4-H), 5.99 (dd, J = 2.9 Hz, J = 1.4 Hz, 1H,
3
3
3
The compound was obtained in a quantitative yield in the
3-H), 6.31 (t, J = 3.0 Hz, 1H, 2-H), 6.41 (dd, J = 7.8 Hz, J
=
trans
3
reaction of 3 and 2,4-dinitrobenzaldehyde (4m); it is a yellow-
15.6 Hz, 1H, olefin. H), 6.64 (d, J
= 15.6 Hz, 1H, olefin. H),
trans
1
brown solid with mp 151–152 °C. The H nmr spectrum in hexa-
6.76 (dd, 1H, 6-H), 6.83 (td, 1H, 8-H), 6.97 (td, 1H, 7-H), 7.19
3
4
deuteriodimethyl sulfoxide contains the following signals: δ 6.12
(m, 2H, pyrrole), 7.06 (m, 2H, pyrrol), 7.28 (dd, 1H, aromatic H),
7.33-7.53 (m, 3H, aromatic H), 8.24 (d, 1H, aromatic H), 8.64
(dd, 1H, aromatic H), 8.82 (d, 1H, aromatic H), 8.99 (s, 1H,
(dd, J = 2.9 Hz, J = 1.5 Hz, 1H, 1-H), 7.23-7.48 ppm (m, 6H, 9-H
13
and other aromatic H); C nmr (deuteriochloroform): δ 56.8 (C-4),
106.5 (C-3), 110.3 (C-2), 113.7, 127.9, 128.5, 128.9, 137.4, 141.6
(aromatic and olefinic C), 114.3/ 114.5 (C-1, C-9), 115.8 (C-6),
119.2 (C-8), 124.6 (C-7), 125.5 (C-9a), 129.6 (C-3a), 136.1 (C-5a);
13
CH=N); C nmr (hexadeuteriodimethyl sulfoxide): δ 109.5,
+•
119.9, 120.2, 122.7, 124.9, 127.4, 128.0, 131.0, 134.3, 135.0,
143.5, 148.3, 148.9 (aromatic C), 158.6 (HC=N).
ms: m/z (%) 272 (100) [M ], 169 (55).
Anal. Calcd for C H N : C, 83.79; H, 5.92; N, 10.29. Found:
19 16
2
Anal. Calcd for C H N O : C, 60.67; H, 3.59; N, 16. 72.
C, 83.72; H, 5.97; N, 10.02.
17 12
4 4
Found: C, 60.67; H, 3.59; N, 16.72.
1,4-Bis(4,5-dihydropyrrolo[1,2-a]quinoxalin-4-yl)benzene (5j).
This compound was obtained from terephthaldehyde (4j) as pale
Acknowledgements.
1
The authors thank COLCIENCIAS and the Universidad del
Valle for financial support. We also thank the DAAD which
granted R. A. for a study visit to the Institute of Organic
Chemistry at the University of Mainz (Germany).
yellow crystals in 84% yield, mp 219-220 °C. The H nmr spectrum
in deuteriochloroform showed signals at δ 4.17 (br s, 2H, N-H) 5.54
3
3
(s, 2H, 4-H), 5.59 (d, J = 3.4 Hz, 2H, 3-H), 6.25 (t, J = 3.4 Hz, 2H,
2-H), 6.71 (d, 2H, 6-H), 6.84 (td, 2H, 8-H), 6.97 (t, 2H, 7-H), 7.19
3
4
(dd, J = 2.9 Hz, J = 1.5 Hz, 2H, 1-H), 7.32 (dd, 2H, 9-H), 7.45
13
(s, 4H, aromatic H); C nmr (deuteriochloroform): δ 55.9 (C-4),
105.9 (C-3), 110.2 (C-2), 114.4/ 114.7 (C-1, C-9), 115.4 (C-6),
119.4 (C-8), 124.7 (C-7), 125.5 (C-9a), 128.4 (aromatic CH), 129.7
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13, 711 (1976).
(C-3a), 136.0 (C-5a), 141.6 (aromatic C ); further small signals at
106.2, 110.3, 115.5, 119.5, 127.6, 129.0 and 134.0 are due to a
diastereomer; ms: m/z (%) 414 (37) [M ], 169 (91).
q
+•
Anal. Calcd for C H N : C, 81.13; H, 5.35; N, 13.52. Found:
28 22
4
C, 80.93; H, 5.42; N, 13.26.
5-Acetyl-4,5-dihydro-4-isopropylpyrrolo[1,2-a]quinoxaline (6k).
This compound was obtained from isobutyraldehyde (4k) as
1
colorless crystals in 70% yield, mp 93-94 °C. The H nmr
spectrum in deuteriochloroform showed signals at δ 0.87 (m, 6H,
CH ), 1.46 (m, 1H, CH, isopropyl), 2.17 (s, 3H, COCH ), 5.56
3
3
3
3
4
(d, J = 10.3 Hz, 1H, 4-H), 6.04 (dd, J = 3.4 Hz, J = 1.0 Hz, 1H,
3
3
4
3-H), 6.27 (t, J = 3.4 Hz, 1H, 2-H), 7.11 (dd, J = 3.4 Hz, J = 1.5
Hz, 1H, 1-H), 7.14-7.30 (m, 3H, 6-H, 7-H, 8-H), 7.39 (d, 1H, 9-
13
H); C nmr (deuteriochloroform): δ 19.0/ 19.3 (CH ), 22.5
3
(COCH ), 30.7 (CH), 55.6 (C-4), 107.2 (C-3), 110.3 (C-2),
3
114.0/ 116.0 (C-1, C-9), 123.9 (C-7), 126.1 (C-6), 126.6 (C-8),
128.3 (C-3a), 129.7 (C-9a), 131.0 (C-5a), 169.4 (C=O); ms: m/z
+•
(%) 254 (16) [M ], 169 (100).
Anal. Calcd for C
H N O: C, 75.56; H, 7.13; N, 11.01.
16 18 2
[11] M. Artico, S. Massa, A. Mai, R. Silvestri and G. Stefancich, J.
Heterocyclic Chem., 29, 241 (1992).
Found: C, 75.37; H, 7.17; N, 10.98.
[12] F. Blicke, Org. Reactions, 1, 303 (1942).
[13] M. Tramontini, Synthesis, 703 (1973).
[14] For these methods see for example: T. D. W. Claridge, High-
Resolution NMR Techniques in Organic Chemistry, Pergamon,
Amsterdam 1999.
5-Acetyl-4,5-dihydro-4-undecylpyrrolo[1,2-a]quinoxaline (6l).
This compound was obtained from dodecanal (4l) as colorless oil
1
in 96% yield. The H nmr spectrum in deuteriochloroform showed
signals at δ 0.85 (t, 3H, CH ), 1.18-1.24 (br m, 20H, CH ), 2.18
3
2