Facile synthesis of model 1,4-dihydro-1h-1,3,4-benzotriazepin-5-ones

Article abstract of DOI:10.1002/jhet.5570390508

2-Aminobenzoic acid reacts readily, in the presence of triethylamine, with hydrazonoyl chlorides (5a-c) (precursors of the reactive nitrile imine 1,3-dipolar species) to afford high yields of the corresponding acyclic amidrazone adducts (6a-c). The latter

Full text of DOI:10.1002/jhet.5570390508

Sep-Oct 2002
Facile Synthesis of Model 1,4-Dihydro-
1H-1,3,4-benzotriazepin-5-ones
901
Bassam A. Abu Thaher [a], Jalal A. Zahra [b] and Mustafa M. El-Abadelah* [b]
[a] Chemistry Department, Faculty of Science, Islamic University of Gaza, Gaza Strip.
[b] Chemistry Department, Faculty of Science, University of Jordan, Amman, Jordan.
Received November 19, 2001
2-Aminobenzoic acid reacts readily, in the presence of triethylamine, with hydrazonoyl chlorides (5a-c)
(precursors of the reactive nitrile imine 1,3-dipolar species) to afford high yields of the corresponding
acyclic amidrazone adducts (6a-c). The latter adducts undergo, in THF in presence of 1,1'-carbonyldiimida-
zole, smooth intramolecular cyclization involving the activated carboxyl and the NH- termini to deliver
unequivocally the respective dihydro-1,3,4-benzotriazepin-5-ones (7a-c).
J. Heterocyclic Chem., 39, 901(2002).
Introduction.
It is worth mentioning that considerable confusion has
surrounded these literature methods, which could have
easily generated varying amounts of the isomeric 3-amino-
quinazolin-4-ones and/or 1,3,4-oxadiazoles. In fact, sev-
eral of the earlier reported syntheses of presumed 1,3,4-
benzotriazepines [6] were later proven erroneous, and the
alternate isomeric structures established [2a,4,7]. The for-
mation of those intervening isomeric five- and six-mem-
bered heterocycles was occasionally suppressed by the
proper choice, adjustment of, and monitoring of the reac-
tion conditions [2c], and was excluded by the use of 1-(2-
aminobenzoyl)-1-methylhydrazides [8,9].
In light of these uncertainties, we thought it was worth-
while to explore alternate preparative avenues starting
from easily accessible compounds. Herein we wish to
report on a convenient and versatile synthetic route toward
new 1,3,4-benzotriazepin-5-ones (7), utilizing hydra-
zonoyl chlorides (5) (Scheme 1).
1,4-benzodiazepines, exemplified by chlorbenzdi-
azepoxide (Librium, 1) and diazepam (Valium, 2) (Chart
1), constitute a unique class of CNS drugs that are widely
used as tranquilizers in several anxiety states [1].
Extensive research in the field of benzodiazepines has
stimulated interest in the synthesis and pharmacologic
action of their aza-homologues, the benzotriazepines.
Amongst these, the 1,3,4-benzotriazepin-5-ones (e.g. 3,
Chart 1) [2-7] have been attended to, but research efforts in
this area were comparatively modest. Their preparation
was reported at large via the reaction of 2-aminobenzoyl-
hydrazides with orthoesters (3a-d) [2], or via the reaction
of 3,1-benzoxazin-4-ones with hydrazine (3e,f) [3], and
once from the reaction of isatoic anhydride with 2-pyridyl-
amidrazone and cyclizing the product with acid (3g) [4].
Some 1,3,4-benzotriazepin-6-ones (4) (Chart 1) were
reported as useful antihypertensives, cardiotonics and
fungicides [5].
Results and Discussion.
Synthesis.
2-Aminobenzoic acid, acting as nitrogen nucleophile in
basic medium, adds readily onto nitrile imines (the reactive
1,3-dipolar intermediates, generated in situ from their
hydrazonyl chloride precursors 5a-c in presence of triethy-
lamine) to furnish the corresponding amidrazone adducts 6
(Scheme 1). This mode of nucleophilic addition reaction of
various nucleophiles onto 1,3-dipoles is well-documented,
and several amidrazone adducts, related to 6, were obtained
from the reaction of primary and secondary amines with
hydrazonoyl chlorides (such as 5) [10,11]. The required
hydrazonoyl chlorides 5a [12-14], 5b [12,13] and 5c [12-
14] were previously characterized, and are made accessible
via the Japp-Klingemann reaction [12,15,16] involving
coupling of the appropriate arenediazonium chloride with
3-chloro-2,4-pentanedione in aqueous pyridine.
In a subsequent step, these acyclic adducts 6 in tetrahydro-
furan in presence of the coupling reagent, 1,1'-carbonyldiim-
idazole, underwent smooth cyclocondensation involving the
activated carboxyl group and the hydrazone-NH terminus to
deliver the requisite benzotriazepinones 7 (Scheme 1).

902
B. A. Abu Thaher, J. A. Zahra and M. M. El-Abadelah
Vol. 39
were preformed at the Microanalytical Laboratory-Inorganic
Chemistry Department, Tübingen University, Germany.
Spectral Data.
The ir, ms, and nmr spectral data and microanalyses of
the new compounds 6a-c and 7a-c conform to the suggested
structures, and are given in the experimental section. Thus,
their ms spectra display the correct molecular ions for
which the measured high-resolution data are in good
1-Arylhydrazono-1-chloropropanones (5a-c).
These hydrazonoyl chlorides were prepared via direct coupling
of the appropriate arenediazonium chloride with 3-chloro-2,4-
pentanedione in aqueous pyridine, following standard procedures
[12,16].
1
agreement with the calculated values. H-signal assign-
ments are straightforward, and C-assignments follow
13
2-[(2-Oxo-1-phenylhydrazonopropan-1-yl)amino]benzoic acid (6a).
from DEPT and 2D (COSY, HMQC and HMBC) experi-
ments. Thus, long range correlation is observed between
H-6 and each of C-9a and C-5 in HMBC experiments for
compounds 7a-c. Likewise, H-8 is correlated with C-5a,
while H-3'/H-5' show correlation with C-1'.
In conclusion, a new synthetic route toward 1,3,4-ben-
zotriazepin-5-ones, described in the present work, utilizes
readily available and inexpensive reactants (anthranilic
acid and hydrazonoyl chlorides). This versatile and effi-
cient route involves two-step reactions that are conve-
niently conducted in a short time, at or below room tem-
perature, to give unequivocally the desired benzotri-
azepinones in good overall yield and high purity. In
essence, this viable method competes favorably with
ambiguous reported methods which also suffered from
inherent drawbacks (vide supra).
A homogeneous solution of 2-aminobenzoic acid (1.65 g, 12
mmol) in aqueous methanol (70%, 20 ml) and triethylamine (3
ml) was added dropwise to a stirred and cooled (0 °C) solution of
1-phenylhydrazono-1-chloropropanone (5a) (2.16 g, 11 mmol) in
tetrahydrofuran (30 ml). Additional triethylamine (3 ml) in
tetrahydrofuran (5 ml) was then introduced dropwise into the
reaction mixture, which was further stirred at 0 °C for 15-20 min-
utes, and then at room temperature for 2-3 hours. The organic sol-
vents were then removed in vacuo from the reaction mixture, and
the residual aqueous solution was directly acidified with glacial
acetic acid (3 ml). The resulting crude solid product was col-
lected, dried and recrystallized from hot chloroform/methanol
(5:1 v/v) as fine yellow needles. Yield of 6a = 82%; mp 210-211
°C; ir (potassium bromide): 3480 (OH), 3310 (NH), 3246 (NH),
1690 (CO), 1603, 1584, 1516, 1491, 1232 cm-1; ms: m/z (% rel.
int.): 297 (M+, 100), 279 (8), 236 (18), 208 (4), 174 (18), 148
(49), 118 (60), 108 (87); hrms: Calcd for C 16H15N3O3:
1
297.111316. Found: 297.108719; H nmr (300 MHz, DMSO-
d6): 2.46 (s, 3H, COCH3), 6.10 (dd, 1H, J = 8.3 Hz, 0.7 Hz,
H-3), 6.78 (m, 1H, H-5), 6.89 (m, 1H, H-4'), 7.22-7.33 (m, 5H,
H-2'/ H-6', H-3'/ H-5' and H-4), 7.88 (dd, 1H, J = 7.9 Hz, 1.6 Hz,
H-6), 9.25 (s, 1H, C2-NH), 10.02 (s, 1H, C1'-NH), 13.10 (s, 1H,
CO2H); 13C nmr (75 MHz, DMSO-d6): d 25.1 (COCH3), 114.2
(C-1), 114.7 (C-2'/C-6'), 115.8 (C-3), 118.5 (C-5), 121.9 (C-4'),
129.5 (C-3'/C-5'), 131.9 (C-6), 134.4 (C-4), 134.9 (NH-C=N-),
144.2 (C-1'), 145.7 (C-2), 170.5 (CO2H), 193.3 (CH3C=O).
Anal. Calcd. for C16H15N3O3 ( 297.32): C, 64.64; H, 5.09; N,
14.13. Found: C, 64.35; H, 5.03; N, 14.11.
EXPERIMENTAL
Melting points (uncorrected) were determined on an elec-
trothermal Mel-Temp. Apparatus. 1H- and 13C nmr spectra were
measured on a Bruker DPX-300 instrument with TMS as internal
reference. Electron-impact mass spectra were obtained using a
Finnigan MAT TSQ-70 spectrometer at 70 eV; ion source tem-
perature = 200 °C. Ir spectra were recorded as KBr discs on a
Nicolet Impact-400 FT-IR spectrophotometer. Microanalyses

Sep-Oct 2002
Facile Synthesis of Model 1,4-Dihydro-1H-1,3,4-benzotriazepin-5-ones
903
2-{[2-Oxo-1-(4-methylphenylhydrazonopropan-1-yl)]amino}-
benzoic Acid (6b).
rated and the residual solid product was recrystallized from
CHCl3/petroleum ether (bp 40-60 °C) forming beige fine crys-
tals. Yield of 7a = 78 %; mp 152-153 °C; ir (potassium bromide):
3319 (NH), 1711 (CO), 1590, 1500, 1465, 1366, 1294, 1270,
1166, 1011 cm-1; ms: m/z (% rel. int.): 279 (M+, 100), 250 (10),
236 (44), 220 (10), 174 (9), 146 (22), 132 (64), 130 (17), 105
(24); hrms : Calcd for C16H13N3O2 : 279.1008. Found :
This compound was prepared from 2-aminobenzoic acid
(1.65 g, 12 mmol) and 1-chloro-1-(4'-methylphenylhydrazono)-
propanone (5b) (2.30 g, 11 mmol) by following the same pro-
cedure and experimental conditions described above for obtain-
ing 6a. The product was recrystallized from chloroform/
methanol as pale yellow prisms. Yield of 6b = 86%; mp 214-
215 °C; ir (potassium bromide): 3466 (OH), 3332 (NH), 3305
(NH), 1674 (CO), 1574, 1555, 1524, 1501, 1244 cm-1; ms: m/z
(% rel. int.): 311 (M+, 84), 293 (13), 250 (7), 222 (4), 189 (26),
174 (13), 148 (26), 146 (28), 132 (100), 106 (74); hrms: Calcd
for C17H17N3O3: 311.1270. Found: 311.1250; 1H nmr (300
MHz, DMSO-d6): 2.20 (s, 3H, C4'-CH3), 2.44 (s, 3H,
COCH3), 6.08 (d, 1H, J = 8.3 Hz, H-3), 6.77 (dd, 1H, J = 7.8
Hz, 7.5 Hz, H-5), 7.06 (d, 2H, J = 8.3 Hz, H-3'/H-5'), 7.22 (d,
2H, J = 8.3 Hz, H-2'/H-6'), 7.29 (m, 1H, H-4), 7.87 (dd, 1H, J =
7.8 Hz, 1.3 Hz, H-6), 9.21 (br s, 1H, C2-NH), 9.97 (s, 1H, C1'-
NH), 13.09 (br s, 1H, CO2H); 13C nmr (75 MHz, DMSO-d6):
20.8 (C4'-CH3), 25.0 (COCH3), 114.1 (C-1), 114.8 (C-2'/C-6'),
115.7 (C-3), 118.4 (C-5), 130.0 (C-3'/C-5'), 130.8 (C-6), 131.8
(C-4), 134.3 (C-4'), 134.4 (NH-C=N-), 141.9 (C-1'), 145.8
(C-2), 170.3 (CO2H), 193.1 (CH3-C=O).
1
279.0975; H nmr (300 MHz, CDCl3): 2.53 (s, 3H, COCH3),
6.72 (dd, 2H, J = 8.5 Hz, 1.1 Hz, H-2'/ H-6'), 6.92 (m, 1H, H-4'),
7.16 (m, 2H, H-3'/ H-5'), 7.46 (br s, 1H, N1-H), 7.43 (m, 1H, H-
7), 7.74 (m, 2H, H-8 / H-9), 8.16 (ddd, 1H, J = 7.6 Hz, 1.9Hz,
1.0Hz, H-6); 13C nmr (75 MHz, CDCl3): 28.7 (COCH3), 114.5
(C-2'/C-6'), 122.4 (C-5a), 122.8 (C-4'), 127.0 (C-6), 128.1 (C-7),
128.2 (C-9), 129.4 (C-3'/C-5'), 135.2 (C-8), 145.7 (C-1'), 146.6
(C-9a), 153.7 (C-2), 160.6 (O=C5-N), 194.2 (CH3C=O).
Anal. Calcld. for C16H13N3O2 (279.3): C, 68.81; H, 4.69; N,
15.04. Found: C, 68.63; H, 4.55; N, 14.86.
2-Acetyl-4-(4-methylphenyl)-1,4-dihydro-1H-1,3,4-benzotri-
azepin-5-one (7b).
This compound was prepared from 6b (3.1 g, 10 mmol) and
1,1'-carbonyldiimidazole (2.0 g, 12.5 mmol) by following the
same procedure and experimental conditions described above for
7a. The product was recrystallized from dichloromethane/n-
hexane as yellow prisms. Yield of 7b = 81%; mp 155-156 °C; ir
(potassium bromide): 3268 (NH), 1705 (CO), 1626, 1606, 1523,
1510, 1344, 1286, 1234, 1130 cm-1; ms: m/z (% rel. int.): 293
(M+, 45), 279 (9), 250 (4), 189 (21), 167 (28), 149 (97), 132 (19),
119 (22), 91 (100); hrms: Calcd for C17H15N3O2: 293.1164.
Found: 293.1117; 1H nmr (300 MHz, CDCl3): 2.38 (s, 3H, C4'-
CH3), 2.43 (s, 3H, COCH3), 6.69 (d, 1H, J = 7.9 Hz, H-8), 6.97
(dd, 1H, J = 7.4 Hz, 7.7 Hz, H-7), 7.23 (d, 2H, J = 8.3 Hz, H-3'/
H-5'), 7.36 (d, 2H, J =8.3 Hz, H-2'/ H-6'), 7.33 (m, 1H, H-9, over-
lapped with H-2'/ H-6'), 7.30 (br s, 1H, N1-H), 7.96 (d, 1H, J =
7.7 Hz, H-6); 13C nmr (75 MHz, CDCl3): 21.2 (C4'-CH3), 24.1
(COCH3), 118.3 (C-8), 121.9 (C-5a), 122.7 (C-7), 126.0 (C-2'/C-
6'), 129.4 (C-3'/C-5'), 134.0 (C-6), 134.6 (C-9), 137.5 (C-4'),
141.5 (C-1'), 143.6 (C-9a), 145.8 (C-2), 165.6 (O=C5-N), 194.0
(CH3C=O).
Anal. Calcd. for C17H17N3O3 ( 311.34): C, 65.58; H, 5.50; N,
13.50. Found: C, 65.44; H, 5.52; N, 13.38.
2-{[2-Oxo-1-(4-chlorophenylhydrazonopropan-1-yl)]amino}-
benzoic Acid (6c).
This compound was prepared from 2-aminobenzoic acid (1.65
g, 12 mmol) and 1-chloro-1-(4'-chlorophenylhydrazono)-
propanone (5c) (2.31 g, 11 mmol) by following the same proce-
dure and experimental conditions described above for obtaining
6a. Recrystallization from chloroform/methanol produced light
orange granules. Yield of 6c = 88%; mp 234-235 °C; ir (potas-
sium bromide): 3450 (OH), 3348 (NH), 3244 (NH), 1695 (CO),
1652, 1586, 1567, 1502, 1490, 1360, 1281, 1240, 1088, 1028
cm-1 ; ms: m/z (% rel. int.): 331 (M+, 100), 313 (30), 270 (11),
235 (13), 174 (28), 148 (95), 126 (97), 125 (88); hrms: Calcd for
1
C16H14ClN3O3: 331.0723. Found: 331.0692; H nmr (300 MHz,
Anal. Calcd. for C17H15N3O2(293.33): C, 69.61; H, 5.15; N,
14.33. Found: C, 69.37; H, 5.02; N, 14.15.
DMSO-d6): 2.46 (s, 3H, COCH3), 6.10 (dd, 1H, J = 8.3 Hz, 0.7
Hz, H-3), 6.79 (ddd, 1H, J = 8.1 Hz, 7.2 Hz, 1.0 Hz, H-5), 7.27-
7.34 (m, 5H, H-2'/ H-6', H-3' / H-5', H-4), 7.89 (dd, 1H, J = 7.2
Hz, 1.5 Hz, H-6), 9.29 (s, 1H, C2-NH), 10.10 (s, 1H, C1'-NH),
13.09 (br s, 1H, CO2H); 13C nmr (75 MHz, DMSO-d6): 25.11
(COCH3), 114.3 (C-1), 115.9 (C-3), 116.2 (C-2'/C-6'), 118.6 (C-
5), 125.4 (C-4'), 129.4 (C-3'/C-5'), 131.9 (C-6), 134.4 (C-4),
135.3 (NH-C=N-), 143.2 (C-1'), 145.4 (C-2), 170.3 (CO2H),
193.4 (CH3-C=O).
2-Aetyl-4-(4-chlorophenyl)-1,4-dihydro-1H-1,3,4-benzotri-
azepin-5-one (7c).
This compound was prepared from 6c (3.3 g, 10 mmol) and 1,1'-
carbonyldiimidazole (2.0 g, 12.5 mmol) by following the same
procedure and experimental conditions described above for 7a.
Recrystallization from dichloromethane/n-hexane gave pale yel-
low granules. Yield of 7c = 83 %; mp 181-182 °C; ir (potassium
bromide): 3313 (NH), 1732 (CO), 1701 (CO), 1608, 1595, 1491,
1467, 1413, 1374, 1168, 1097 cm-1; ms: m/z (% rel. int.): 313 (M+,
94), 278 (3), 270 (21), 254 (10), 235 (22), 189 (10), 174 (13), 146
(25), 132 (58), 126 (84), 125 (100), 111 (63); hrms: Calcd for
Anal. Calcd. for C16H14ClN3O3 ( 331.76): C, 57.93; H, 4.25;
Cl, 10.69; N, 12.67. Found: C, 57.68; H, 4.15; Cl, 10.53; N,
12.58.
2-Acetyl-4-phenyl-1,4-dihydro-1H-1,3,4-benzotriazepin-5-one
(7a).
1
C16H12ClN3O2: 313.0618. Found: 313.0592; H nmr (300 MHz,
CDCl3): 2.57 (s, 3H, COCH3), 6.69 (m, 2H, H-2'/ H-6'), 7.16 (m,
2H, H-3'/ H-5'), 7.20 (br s, 1H, N1-H), 7.54 (ddd, 1H, J = 8.0 Hz,
6.3 Hz, 1.5 Hz, H-7), 7.79 (m, 2H, H-8 / H-9), 8.22 (dd, 1H, J = 8.0
Hz, 1.5 Hz, H-6); 13C nmr (75 MHz, CDCl3): 28.6 (COCH3),
116.0 (C-2'/ C-6'), 122.3 (C-5a), 127.2 (C-6), 128.1 (C-4'), 128.3
(C-9), 128.4 (C-7), 129.4 (C-3'/ C-5'), 135.3 (C-8), 144.3 (C-1'),
To a mixture of 1,1'-carbonyldiimidazole (2.0 g, 12.5 mmol)
and compound 6a (3.0 g, 10 mmol) was added dry tetrahydrofu-
ran (50 ml), and the resulting solution was stirred at room tem-
perature for 1-2 hours. The solvent was then removed in vacuo
and the residue was immediately treated with water (40 ml) and
extracted with chloroform (2 x 40 ml). The combined organic
extracts were dried (Na2SO4), the solvent chloroform was evapo-
146.4 (C-9a), 152.9 (C-2), 160.5 (O=C5-N), 193.9 (CH C=O).
3

904
B. A. Abu Thaher, J. A. Zahra and M. M. El-Abadelah
Vol. 39
489 (1969); [c] C. K. Reddy, P.S.N. Reddy and C. V. Ratnam,
Synthesis, 842 (1983); [d] A. M. M. E. Omar, F. A. Ashour and J.
Bourdais, J. Heterocyclic Chem., 16, 1435 (1979); [e] J. S. Davidson,
"Abstracts of the English International Congress of Heterocyclic
Chemistry" p. 214 (1981); [f] A. L. Langis, US 3 542 767 (1970)
Chem. Abstr., 74, 88089x (1971); [g] G. M. Reddy and P. S. N.
Reddy, Indian J. Chem., 36B, 166 (1997).
[7a] N. P. Peet, S. Sunder and D. L. Trepanier, Indian. J.
Chem., 14B, 701 (1976); [b] M. J. Kornet, J. Pharm. Sci., 62, 834
(1973); [c] S. Sunder, N. P. Peet and R. J. Barbuch, J. Heterocyclic
Chem., 18, 1601 (1981); [d] E. Tihanyi, M. Jal and P. Dvorstak,
Heterocycles, 20, 571 (1983); [e] G. M. Reddy and P. S. N. Reddy,
Indian J. Chem., 37B, 207 (1998).
Anal. Calcd. for C16H12ClN3O2 ( 313.75): C, 61.25; H, 3.86;
Cl, 11.30; N, 13.39. Found: C, 61.12; H, 3.81; Cl, 11.18; N,
13.35.
Acknowledgement.
We wish to thank the Advanced Pharmaceutical Industries Co.
Ltd., Amman-Jordan for financial support.
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