New and efficient synthesis of 6,11-dihydro-11-ethyl-5H-dibenz[b,e]azepine derivatives starting from N-benzylanilines via amino-Claisen and Friedel-Crafts methodologies

Article abstract of DOI:10.1055/s-2004-836026

New and efficient synthesis of 6,11-dihydro-11-ethyl-5H-dibenz[b,e]azepine derivatives, using the key steps of BF₃·OEt ₂-catalyzed aromatic amino-Claisen rearrangement and the intramolecular alkene Friedel-Crafts alkylation, is reported.

Full text of DOI:10.1055/s-2004-836026

LETTER
2721
New and Efficient Synthesis of 6,11-Dihydro-11-ethyl-5H-dibenz[b,e]azepine
Derivatives Starting from N-Benzylanilines via Amino-Claisen and Friedel–
Crafts Methodologies
S
ynthesis of 6,11-
l
ihydro
i
-11-et
r
H
-d
i
ibenz[
o
,
e
]azepine Derivat
P
ives alma,a Jacqueline Jaimes Barajas,a Vladimir V. Kouznetsov,*a Elena Stashenko,a Ali Bahsas,b
Juan Amaro-Luisb
a
Laboratorio de Síntesis Orgánica Fina, Centro de Investigación en Biomoléculas, Escuela de Química, Universidad Industrial de
Santander, A.A. 678, Bucaramanga, Colombia
Fax +57(76)349069; E-mail: kouznet@uis.edu.co
b
Laboratorio de RMN, Grupo de Productos Naturales, Departamento de Química, Universidad de los Andes, Mérida 5101, Venezuela
Received 4 May 2004
CH3
Abstract: New and efficient synthesis of 6,11-dihydro-11-ethyl-
5H-dibenz[b,e]azepine derivatives, using the key steps of
BF3·OEt2-catalyzed aromatic amino-Claisen rearrangement and the
intramolecular alkene Friedel–Crafts alkylation, is reported.
R
R
R
N
H
N
H
N
Key words: dibenz[b,e]azepine derivatives, amino-Claisen rear-
rangement, N-allylation, intramolecular alkene Friedel–Crafts
alkylation
Scheme 1
The synthesis of the dibenz[b,e]azepine ring has attracted
a wide interest as several derivatives of this heterocyclic
unit have been found to be biologically active as anti-de-
pressive,1,2 anxiolytic,3,4 anti-inflammatory,5–7 and anti-
allergic8 agents.
In the synthesis of dibenz[b,e]azepines, anthranilic acid9
and ortho-aminobenzylic alcohol4,10 derivatives as well as
anthraquinone derivatives11 are the most widely used
precursors. However, to the best of our knowledge, the
possibility to easily prepare this heterocyclic core using
the broad scope of intramolecular alkene Friedel–Crafts
alkylation in the series of N-benzyl-o-allylanilines has not
been explored yet.
by Friedel–Crafts alkylation reaction becomes trouble-
some.21 We wish here to report a new and efficient syn-
thesis of 6,11-dihydro-11-ethyl-5H-dibenz[b,e]azepine
derivatives starting from readily available substituted
anilines and benzaldehyde.
Thus, a wide range of substituted anilines and benzalde-
hyde were subjected to the reductive amination process22
to produce secondary N-benzylanilines 1a–e in high
yields. N-Allylation reaction of anilines 1a–e was per-
formed by the conventional procedure with an excess (2
equiv) of allylbromide in DMF at room temperature or in
acetone in the presence of potassium carbonate (K2CO3)
under reflux to afford the N-allyl-N-benzylanilines 2a–e
in 53–91% yields as clear viscous oils (Scheme 2).
We have been studying for several years the intramo-
lecular Friedel–Crafts alkylation process as the key step in
the construction of diverse N-containing polyhetero-
cycles.12–17
In the second step, a solution of compounds 2 and
equimolar amounts of boron trifluoride–diethyl ether
complex (BF3·OEt2) in sulpholane was heated at 140–
155 °C.23 The reaction mixture was then allowed to react
for 2–3 h (TLC control) to give the desired rearranged
products 3a–d,24 which were isolated by silica gel column
chromatography as viscous oils in good yields, essentially
unaffected by the nature of substituents on the benzene
ring of anilines (Table 1). In the case of the amino-Claisen
rearrangement of compound 2e, the allylic group migrates
to both free ortho positions with formation of two regio-
isomeric products corresponding to 2-allyl-N-benzyl-5-
methylaniline (3e) and 2-allyl-N-benzyl-3-methylaniline
(3e¢) in a 0.8:1 ratio (determined by NMR spectroscopy),
which we could not separate.
In continuation of our research program on the prepara-
tion of new potential CNS-active molecules, we needed a
simple and inexpensive synthesis of 6,11-dihydro-11-eth-
yl-5H-dibenz[b,e]azepine derivatives. Analyzing the retro
synthetic pathway for the dibenz[b,e]azepine structures
depicted in Scheme 1, we inferred that the N-benzyl-o-
allyl-anilines could be useful precursors in its synthesis.
To obtain these key intermediates, we addressed to pow-
erful Claisen rearrangement methodology, taking into
consideration that the amino-Claisen rearrangement in the
aromatic systems has received a great attention in the last
decades due to its potential synthetic utility in organic
synthesis,18–20 and that the ortho-allylation of anilines
Finally, compounds 3a–d were heated at 80–90 °C with
concentrated sulfuric acid for 1.5–2.5 h. Under these
acidic conditions, the allyl moiety of molecules 3 provides
an appropriate handle to generate the necessary and
thermodynamically stable benzyl cation. Therefore the
SYNLETT 2004, No. 15, pp 2721–2724
0
7
.1
2
.2
0
0
4
Advanced online publication: 25.11.2004
DOI: 10.1055/s-2004-836026; Art ID: S03804ST
© Georg Thieme Verlag Stuttgart · New York

2722
A. Palma et al.
LETTER
+
H3C
N
H
H3C
N
H
(0.8:1.0; 73%)
3e
3e′
ii
R2
R1
R2
R1
R2
1. ArCHO/EtOH
2. NaBH4/MeOH
i
R1
N
NH2
N
H
R
R
R
2a–e (53–91%)
1a–e (79–86%)
a) R = R1 = R2 = H
b) R = R1 = H, R2 = Cl
c) R = R1 = H, R2 = F
d) R = CH3, R1 = Cl, R2 = H
e) R = R2 = H, R1 = CH3
13
CH3
ii
12
1
R2
R1
2
R2
R1
11
iii
3
5
N
6
N
H
4
R
R
H
4a–d (78–85%)
3a–d (72–85%)
Scheme 2 Reagents and conditions: (i) BrCH2CH=CH2 (2 equiv), DMF, r.t. or acetone, K2CO3, reflux, 6–7 h; (ii) BF3·OEt2 (1 equiv),
sulpholane (3–5 mL), 140–155 °C, 2–3 h; (iii) concd H2SO4, 80–90 °C, 1.5–2.5 h.
intramolecular Friedel–Crafts alkylation of the second Table 1 Amino-Claisen Rearrangement of 2a–e to 3a–e
benzene ring can be realized. Treatment of the reaction
Entry N-Allylaniline
Condi-
tions
Rearranged
product
Yield
(%)
mixture with 25% ammonia solution, and extraction and
purification by silica gel column chromatography afford-
ed compounds 4a–d in good yields (78–85%). Longer
reaction times and higher temperatures resulted in the de-
composition of key intermediates 3a–d.
1
155 °C
2.5 h
80
N
Ph
N
H
Ph
1
All spectroscopic data (IR, MS and H NMR, 13C NMR)
3a
2a
Cl
of final products 4a–d are in full agreement with the pro-
posed structures.25 These compounds showed absorption
bands at 3446–3405 cm–1 due to amino group (N-H) in the
IR spectra. In the electron impact (EI) MS, molecular ion
peaks were observed at m/z (%) = 223 (14) [M+], 257
(35Cl, 17) [M+], 241 (17) [M+] and 271 (35Cl, 13) [M+]
together with their fragment ion peaks M+ – C2H5 as base
peaks.
2
140 °C
3 h
73
Cl
N
Ph
N
H
Ph
3b
2b
F
3
4
5
140 °C
3 h
72
85
73
F
N
Ph
N
H
Ph
The most clear spectral proof for the structures 4 was the
appearance of two triplets assignable to 11-CH (d = 3.84–
3.63 ppm, J = 7.7–7.3 Hz) and 13-CH3 (d = 0.96–0.91
ppm, J = 7.4–7.0 Hz), and a multiplet assignable to 12-
CH2 protons (d = 2.23–2.14 ppm). The spectra also
showed two doublets (d = 4.95–4.71 and 4.30–4.00 ppm,
J = 14.8–14.4 Hz) attributed to 6-CHAHB protons, while
the corresponding peaks of precursors 3 were singlets
(d = 4.34–4.09 ppm). The signal of NH proton is observed
only in spectrum of compound 4d at d = 4.09 ppm, while
for other compounds this signal is not evident because it
may be overlapped with the signal of proton 6-HB.
3c
2c
140 °C
2 h
Cl
N
Ph
Cl
N
H
Ph
CH3
CH3
3d
2d
155 °C
2.5 h
H3C
N
Ph
H3C
N
Ph
H
3e
2e
This way, we have been demonstrated that BF3·Et2O-cat-
alyzed aromatic amino-Claisen rearrangement and in-
tramolecular alkene Friedel–Crafts alkylation could gain
prominence as a synthetically useful reactions to build the
dibenz[b,e]azepine structural unit, which occurs in a
number of bioactive molecules for a variety of biological
targets, in particular, the tetracyclic antidepressants such
as mianserin and its close relative analogues. The good
yields of intermediates and final products as well as the
H3C
N
H
Ph
3e¢
Synlett 2004, No. 15, 2721–2724 © Thieme Stuttgart · New York

LETTER
Synthesis of 6,11-Dihydro-11-ethyl-5H-dibenz[b,e]azepine Derivatives
2723
(18) Baxter, E. W.; Labaree, D.; Ammon, H. L.; Mariano, P. S. J.
Am. Chem. Soc. 1990, 112, 7682.
(19) Barta, N. S.; Cook, G. R.; Landis, M. S.; Stille, J. R. J. Org.
Chem. 1992, 57, 7188.
(20) Lai, G.; Anderson, W. K. Tetrahedron Lett. 1993, 34, 6849.
(21) Stroh, R.; Ebersberger, J.; Haberland, H.; Hahn, W. Angew.
Chem. 1957, 69, 124.
general applicability accommodating a variety of substi-
tutions on both aromatic rings are the main advantages of
our approach. Further application of these methodologies
in synthesis of other nitrogen containing heterocycles is
currently under way in our laboratory.
(22) Borch, R. F.; Bernstein, M. D.; Durst, H. D. J. Am. Chem.
Soc. 1971, 93, 2897.
Acknowledgment
(23) Anderson, W. K.; Lai, G. Synthesis 1995, 1287.
(24) Spectral Data for Selected Compounds 3.
Compound 3b: 1H NMR (400 MHz, CDCl3): d = 3.29 (2 H,
d, J = 6.0 Hz, -CH2-), 4.10 (1 H, br s, NH), 4.34 (2 H, s, N-
CH2-), 5.15 (2 H, m, =CH2), 5.95 (1 H, m, -CH=), 6.54 (1 H,
d, J = 8.0 Hz, 6-H), 7.06 (1 H, d, J = 2.0 Hz, 3-H), 7.08 (1 H,
The authors are grateful for the financial support by the Colombian
Institute for Science and Research (Colciencias, grant No 1102-05-
13567).
References
dd, J = 8.0, 2.0 Hz, 5-H), 7.30–7.43 (5 H, m, H-phenyl). 13
C
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NMR (100 MHz, CDCl3): d = 36.1 (-CH2-), 48.2 (N-CH2-),
111.8 (6-C), 116.9 (=CH2), 122.0 (4-C), 125.2 (2-C), 127.3
(ortho-C), 127.4 (5-C), 128.7 (3-C), 129.0 (para-C), 129.5
(meta-C), 135.0 (-CH=), 139.0 (1¢-C), 144.6 (1-C). MS (EI):
m/z (%) = 257 (35Cl, 8) [M+], 242 (<1), 228 (1), 180 (11), 166
(26), 152 (11), 131 (40), 91 (100), 77 (10).
(3) Sipido, V. K.; Fernández-Gadea, F. J.; Andrés-Gil, J. I.;
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Yamaguchi, T. U.S. US 5476848, 1995; Chem. Abstr. 1996,
124, 261063k.
Compound 3c: 1H NMR (400 MHz, CDCl3): d = 3.32 (2 H,
d, J = 6.4 Hz, -CH2-), 4.06 (1 H, br s, NH), 4.34 (2 H, s, N-
CH2-), 5.15 (2 H, m, =CH2), 5.97 (1 H, m, -CH=), 6.56 (1 H,
dd, J = 9.0, 5.0 Hz, 6-H), 6.83 (1 H, d, J = 3.0 Hz, 3-H), 6.85
(1 H, dd, J = 9.0, 3.0 Hz, 5-H), 7.30–7.39 (5 H, m, H-
phenyl). 13C NMR (100 MHz, CDCl3): d = 36.2 (-CH2-),
48.7 (N-CH2-), 111.5 (d, J = 10.0 Hz. 6-C), 113.4 (d,
J = 20.0 Hz, 3-C), 116.5 (d, J = 20.0 Hz, 5-C), 116.9
(=CH2), 125.3 (d, J = 10.0 Hz, 2-C), 127.2 (para-C), 127.5
(ortho-C), 128.5 (meta-C), 135.1 (-CH=), 139.3 (1¢-C),
142.3 (1-C), 155.6 (d, J = 206.1 Hz, 4-C). MS (EI):
m/z (%) = 241 (28) [M+], 212 (8), 198 (4), 164 (9), 150 (66),
135 (17), 91 (100), 77 (6), 65 (21).
Compound 3d: 1H NMR (400 MHz, CDCl3): d = 2.44 (3 H,
s, 2-CH3), 3.29 (2 H, dt, J = 6.0, 1.6 Hz, -CH2-), 3.04 (1 H,
br s, NH), 4.09 (2 H, s, N-CH2-), 5.05 (2 H, m, =CH2), 5.93
(1 H, m, -CH=), 6.95 (1 H, d, J = 8.0 Hz, 5-H), 7.07 (1 H, d,
J = 8.0 Hz, 4-H), 7.33–7.40 (5 H, m, H-phenyl). 13C NMR
(100 MHz, CDCl3): d = 15.6 (2-CH3), 36.3 (-CH2-), 53.6 (N-
CH2-), 116.9 (=CH2), 123.4 (4-C), 127.4 (ortho-C), 127.8
(5-C), 128.3 (para-C), 128.6 (meta-C), 129.4 (3-C), 130.4
(6-C), 133.7 (2-C), 136.5 (-CH=), 139.0 (1¢-C), 147.4 (1-C).
MS (EI): m/z (%) = 271 (35Cl, 11) [M+], 256 (2), 242 (4), 194
(7), 180 (33), 166 (18), 145 (46), 130 (14), 115 (8), 91 (100),
77 (8), 65 (22).
(9) Sinha, A. K.; Nizamuddin, S. Ind. J. Chem., Sect. B 1984, 23,
83.
(10) (a) Sasakura, K.; Sugasawa, T. Heterocycles 1981, 15, 421.
(b) Lypacewicz, M. K.; Poslinska-Bucewka, H.; Smolinska,
J.; Wasiak, T.; Sosinska, D.; Mostrak, M.; Trzpil, B.;
Paszkowski, S. Pol. PL 175287, 1998; Chem. Abstr. 1999,
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den Bergh, L.; Agten, J.; Lambrechts, A.; Van den Heurel,
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(11) (a) Moriconi, E. J.; Maniscalco, I. A. J. Org. Chem. 1972,
37, 208. (b) Sinha, A. K.; Nizamuddin, S. Ind. J. Chem.,
Sect. B 1984, 23, 165.
(12) Kouznetsov, V.; Palma, A. R.; Salas, S.; Vargas, L. Y.;
Zubkov, F. I.; Varlamov, A. V.; Martínez, J. R. J.
Heterocycl. Chem. 1997, 34, 1591.
(13) Palma, A. R.; Rozo, W.; Stashenko, E.; Molina, D.;
Kouznetsov, V. J. Heterocycl. Chem. 1998, 35, 183.
(14) Kouznetsov, V.; Palma, A.; Rozo, W.; Stashenko, E.;
Bahsas, A.; Amaro-Luis, J. Tetrahedron Lett. 2000, 41,
6985.
(25) NMR and Analytical Data for Compounds 4.
Compound 4a: IR (KBr): 3405 cm–1. 1H NMR (400 MHz,
CDCl3): d = 0.91 (3 H, t, J = 7.4 Hz, 13-H), 2.17 (2 H, m,
12-H), 3.69 (1 H, t, J = 7.3 Hz, 11-H), 4.00 (1 H, d, J = 14.8
Hz, 6-HB), 4.95 (1 H, d, J = 14.8 Hz, 6-HA), 6.50 (1 H, d,
J = 8.0 Hz, 4-H), 6.67 (1 H, td, J = 8.0, 1.0 Hz, 2-H), 6.96
(1 H, td, J = 8.0, 1.0 Hz, 3-H), 7.12 (1 H, dd, J = 8.0, 1.0 Hz,
1-H), 7.19–7.30 (4 H, m, 7-H-10-H). 13C NMR (100 MHz,
CDCl3): d = 13.0 (13-C), 31.6 (12-C), 51.1 (6-C), 54.8 (11-
C), 117.9 (4-C), 118.2 (2-C), 127.2 (3-C), 127.6-129.5 (7-C-
10-C), 130.2 (11a-C), 130.8 (1-C), 136.5 (6a-C), 142.1 (10a-
C), 146.2 (4a-C). MS (EI): m/z (%) = 223 (14) [M+], 194
(100), 178 (8), 165 (11), 116 (10), 96 (10). Anal. Calcd for
C16H17N: C, 86.06; H, 7.67; N, 6.27. Found: C, 86.13; H,
7.81; N, 6.14.
(15) Varlamov, A.; Kouznetsov, V.; Zubkov, F.; Chernyshev, A.;
Alexandrov, G.; Palma, A.; Vargas, L.; Salas, S. Synthesis
2001, 849.
(16) Palma, A.; Salas, S.; Kouznetsov, V.; Stashenko, E.;
Montenegro, N. G.; Fontela, G. A. J. Heterocycl. Chem.
2001, 38, 837.
Compound 4b: IR (KBr): 3406 cm–1. 1H NMR (400 MHz,
CDCl3): d = 0.91 (3 H, t, J = 7.3 Hz, 13-H), 2.14 (2 H, m,
12-H), 3.63 (1 H, t, J = 7.7 Hz, 11-H), 4.17 (1 H, d, J = 14.4
Hz, 6-HB), 4.77 (1 H, d, J = 14.4 Hz, 6-HA), 6.40 (1 H, d,
J = 8.5 Hz, 4-H), 6.91 (1 H, dd, J = 8.5, 2.3 Hz, 3-H), 7.10
(17) Kouznetsov, V.; Palma, A.; Rozo, W.; Stashenko, E.;
Bahsas, A.; Amaro-Luis, J. Synth. Commun. 2002, 32, 2965.
Synlett 2004, No. 15, 2721–2724 © Thieme Stuttgart · New York

2724
A. Palma et al.
LETTER
(1 H, d, 2.3 Hz, 1-H), 7.12–7.34 (4 H, m, 7-H-10-H). 13
C
(d, J = 230 Hz, 2-C). MS (EI): m/z (%) = 241 (17) [M+], 212
(100), 196 (15), 183 (17), 165(10), 116 (9). Anal. Calcd for
C16H16FN: C, 79.64; H, 6.68; N, 5.80.Found: C, 79.70; H,
6.80; N, 5.65.
NMR (100 MHz, CDCl3): d = 13.3 (13-C), 31.5 (12-C), 49.5
(6-C), 51.5 (11-C), 119.4 (4-C), 122.9 (2-C), 127.4 (3-C),
127.4–128.7 (7-C-10-C), 129.1 (11a-C), 130.7 (1-C), 136.5
(6a-C), 142.0 (10a-C), 145.1 (4a-C). MS (EI): m/z (%) = 257
(35Cl, 17) [M+], 228 (100), 193 (46), 165 (17), 115 (6), 89
(5). Anal. Calcd for C16H16ClN: C, 74.56; H, 6.26; N, 5.43.
Found: C, 74.38; H, 6.49; N, 5.35.
Compound 4d: IR (KBr): 3446 cm–1. 1H NMR (400 MHz,
CDCl3): d = 0.96 (3 H, t, J = 7.4 Hz, 13-H), 2.20 (3 H, s, 4-
CH3), 2.23 (2 H, m, 12-H), 3.84 (1 H, t, J = 7.6 Hz, 11-H),
4.09 (1 H, br s, N-H), 4.3 (1 H, d, J = 14.6 Hz, 6-HB), 4.90
(1 H, d, J = 14.6 Hz, 6-HA), 6.78 (1 H, d, J = 8.3 Hz, 2-H),
6.92 (1 H, d, J = 8.3 Hz, 1-H), 7.18–7.29 (4 H, m, 7-H-10-
H). 13C NMR (100 MHz, CDCl3): d = 11.9 (13-C), 13.3 (4-
CH3), 29.9 (12-C), 48.0 (6-C), 52.5 (11-C), 117.5 (3-C),
120.3 (2-C), 124.9 (4-C), 125.9 (9-C), 126.5 (7-C), 127.0 (8-
C), 127.7 (10-C), 127.8 (1-C), 131.8 (11a-C), 135.3 (6a-C),
140.9 (10a-C), 144.4 (4a-C). MS (EI): m/z (%) = 271 (35Cl,
13) [M+], 242 (100), 227 (6), 207 (31), 191 (10), 178 (11),
165 (8), 152 (6), 139 (2), 89 (4). Anal. Calcd for C17 H18ClN:
C, 75.13; H, 6.68; N, 5.15. Found: C, 75.29; H, 6.83; N, 5.08.
Compound 4c: IR (KBr): 3429 cm–1. 1H NMR (400 MHz,
CDCl3): d = 0.91 (3 H, t, J = 7.1 Hz, 13-H), 2.18 (2 H, m,
12-H), 3.76 (1 H, t, J = 7.6 Hz, 11-H), 4.20 (1 H, d, J = 14.6
Hz, 6-HB), 4.71 (1 H, d, J = 14.6 Hz, 6-HA), 6.49 (1 H, dd,
J = 8.0, 5.0 Hz, 4-H), 6.72 (1 H, ddd, J = 8.0, 3.0 Hz, 3-H),
6.82 (1 H, dd, J = 10.0, 3.0 Hz, 1-H), 7.13–7.22 (4 H, m, 7-
H-10-H). 13C NMR (100 MHz, CDCl3): d = 12.9 (13-C),
30.8 (12-C), 49.7 (6-C), 53.1 (11-C), 113.7 (d, J = 20 Hz, 3-
C), 116.7 (d, J = 20 Hz, 1-C), 119.5 (d, J = 10 Hz, 4-C),
126.8 (8-C), 127.4 (9-C), 128.2 (7-C), 129.1 (10-C), 130.0
(11a-C), 136.5 (6a-C), 141.3 (10a-C), 142.5 (4a-C), 156.4
Synlett 2004, No. 15, 2721–2724 © Thieme Stuttgart · New York