Sulfamic acid: An efficient and green catalyst for synthesis of 1,5-benzodiazepines under solvent-free conditions

Article abstract of DOI:10.1002/hc.20305

It is described that sulfamic acid can be utilized as an effective and green catalyst for the synthesis of 1,5-benzodiazepines in high yields from the solvent-free condensation of o-phenylenediamine (1) and ketones (2). 2007 Wiley Periodicals, Inc.

Full text of DOI:10.1002/hc.20305

Heteroatom Chemistry
Volume 18, Number 4, 2007
Sulfamic Acid: An Efficient and Green Catalyst
for Synthesis of 1,5-Benzodiazepines Under
Solvent-Free Conditions
Min Xia and Yue-dong Lu
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, P.R. China
Received 6 February 2006; revised 15 March 2006
densations, the presence of an acidic catalyst is in-
ABSTRACT: It is described that sulfamic acid can
dispensable, like BF3·OEt [9], polyphosphoric acid
be utilized as an effective and green catalyst for the
synthesis of 1,5-benzodiazepines in high yields from
[10], MgO/POCl3 [11], Yb(OTf)3 [12], Me2S+BrBr−
[13], Sc(OTf)3 [14], PVP-supported FeCl3 [15], I2
the solvent-free condensation of o-phenylenediamine
[16], Ag3PW12O40 [17], InBr3 [18], SO24−/ZrO2 [19],
ꢀ
C
(1) and ketones (2).
2007 Wiley Periodicals, Inc.
[(L)proline]2Zn [20], Al2O3/P2O5 [21], etc are reported
to catalyzed the formation of 1,5-benzodiazepines.
Moreover, the approach to these significant species
can also be achieved by microwave irradiation in
the aid of CH3COOH [22] or executed in ionic
liquid medium [23]. Besides, Zhang et al. de-
scribed an alternative strategy [24] for the trans-
formation of o-nitrophenylazide and ketones to 1,5-
benzodiazepines through the reductive cyclization
in the TiCl4/Sm system. However, most of these
methodologies are associated with several draw-
backs, such as prolonged reaction time, harsh re-
action conditions, difficulty recycling catalysts, low
product yields, occurrence of several side reactions,
much expensive catalysts, heavy environment pollu-
tion, and so on.
In the past 3 years, owing to its prominent
physical and chemical property like outstanding
stability, nontoxicity, nonvolatility, odorlessness,
ready availability, and extremely cheap price,∗ sul-
famic acid (SA) has increasingly attracted much
attention as an alternative acidic catalyst in some
heterogeneously catalytic reactions like acetaliza-
tion [25], esterification [26], acetylation of alcohols
and phenols [27], nitrile formation [28], tetrahy-
dropyranylation of alcohols [29], transesterification
Heteroatom Chem 18:354–358, 2007; Published online
in Wiley InterScience (www.interscience.wiley.com). DOI
10.1002/hc.20305
INTRODUCTION
Benzodiazepines and their polycyclic derivatives
are a very important family of bioactive com-
pounds. They are widely used as anticonvulsant, an-
tiinflammatory, analgesic, hypnotic, sedative, and
antidepressive reagents [1,2] and their new ap-
plications have been increasingly found. Besides,
benzodiazepines are also significant intermediates
in the constructions of fused-ring compounds such
as triazolo-, oxadiazolo-, oxazino-, and furanoben-
zodiazepines [3–6]. Owing to their broad spec-
trum of biological activity, these compounds have
received a great deal of attention in connection
with their synthesis. Generally, the routes to them
include the condensation of o-phenylenediamines
with α,β-unsaturated carbonyl compounds [7], β-
haloketones, or with ketones [8]. To drive the con-
Correspondence to: Min Xia; e-mail: xiamin@hzcnc.com.
Contract grant sponsor: Nature Science Foundation of China.
Contract grant number: 20402013.
2007 Wiley Periodicals, Inc.
∗ In China, the price of sulfamic acid is $1 per 100 g.
c
ꢀ
354

Sulfamic Acid 355
of β-ketoesters [30], acetolysis of cyclic ethers
[31], protection of carbonyls [32], Biginelli [33]
and Pechmann condensation [34], Bechmann re-
arrangement [35], imino-Diels-Alder reaction [36],
synthesis of quinolines [37], benzoxanthenes [38],
bis(indolyl)methanes [39], and so on. However, there
is no report in the literature on the utilization of SA
in the synthesis of benzodiazepines via the cycliza-
tion of o-phenylenediamine and ketones. The dis-
tinctive catalytic activity and intrinsic zwitterionic
feature of SA makes it much different from conven-
tional acidic catalysts and encourages us to inves-
tigate its application in the formation of benzodi-
azepines. The use of recyclable SA makes the process
convenient, economic, and environmentally benign
with rapid access to products in good to excellent
yields under mild conditions.
3b: mp 141–143◦C) Lit. [17] 137–139◦C); FT-IR
(KBr) ν: 3332, 2967, 2932, 1639, 1596, 1471, 750
1
cm−1; H NMR (400 MHz, CDCl3) δ: 0.94 (t, J = 7.6
Hz, 3H, CH2 CH3), 1.24 (t, J = 7.6 Hz, 3H, N C CH2
CH3), 1.26 (s, 3H, CH3), 1.56–1.70 (m, 2H, CH2CH3),
2.14 (d, J = 13.2 Hz, 1H, CHa2), 2.23 (d, J = 13.2 Hz,
1H, CHb2), 2.59 (q, J = 7.6 Hz, 2H, N C CH2), 3.01
(br, s, 1H, NH), 6.71–6.74 (m, 1H, Ar H), 6.96–6.98
(m, 2H, Ar Hs), 7.11–7.14 (m, 1H, Ar H); EI-MS (70
eV) m/z (%): 217 (M+ + 1, 100), 187 (95), 145 (22),
133 (20), 119 (7), 92 (6), 77 (10), 65 (11).
3bꢁ: mp 135–136◦C (Lit. [40] 139–141◦C); FT-IR
(KBr) ν: 3381, 2982, 1635, 1601, 1477, 765 cm−1;
1H NMR (400 MHz, CDCl3) δ: 0.98 (t, J = 7.0 Hz,
3H, CH3CH2 ), 1.25 (s, 3H, CH3 ), 1.51–1.64 (m,
2H, CH2CH3), 1.75 (m, 3H, CH CH3), 2.51 (s, 3H,
N C CH3), 2.85 (m, 1H, N C CH), 3.55 (s, br, NH),
6.67–6.70 (m, 1H, Ar H), 6.94 (m, 2H, Ar Hs), 7.06–
7.11 (m, 1H, Ar H); EI-MS (70 eV) m/z (%): 216 (M+,
100), 193 (11), 187 (75), 155 (42), 141 (20), 131 (6),
118 (17), 77 (30).
EXPERIMENTAL
3c: mp 142–144◦C (Lit. [12] 144–145◦C); FT-IR
(KBr) ν: 3323, 2982, 2876, 1654, 1605, 1475, 778
Apparatus and Analysis
All the compounds used were analytical reagents
and some chemicals were further purified by re-
1
cm−1; H NMR (400 MHz, CDCl3) δ: 0.77–1.10 (m,
9H, CH3CH2 ), 1.23–1.41 (m, 4H, CH3 CH2 ), 1.53–
1.67 (m, 3H, CHCH3), 2.41–2.63 (m, 2H, N C
CH2CH3), 2.89 (q, J = 7.2 Hz, 1H, N C CH CH3),
3.91 (br, s, 1H, NH), 6.57 (d, J = 8.0 Hz, 1H, Ar H),
6.65 (t, J = 8.0 Hz, 1H, Ar H), 6.93 (t, J = 8.2 Hz,
1H, Ar H), 7.33 (d, J = 8.2 Hz, 1H, Ar H); EI-MS
(70 eV) m/z (%): 244 (M+, 30), 229 (25), 215 (100),
114 (15), 77 (25), 65 (13).
1
crystallization or distillation. H NMR spectra were
obtained on a Bruker Avance DMX 400 MHz instru-
ment using TMS as internal standard in CDCl3. FT-
IR spectra were recorded on a Nicolet Avatar spec-
trophotometer. EI-MS were carried out on a Varian
GC-MS spectrometer.
3d: mp 134–135◦C (Lit. [12] 138–139◦C); FT-IR
(KBr) ν: 3340, 2966, 2872, 1642, 1605, 1503, 1264,
General Procedure
1
A mixture of o-phenylenediamine 1 (1 mmol,
0.103 g), ketone 2 (2.2 mmol), and SA (0.2 mmol,
0.02 g) was stirred under solvent-free conditions at
appropriate temperature for appropriate time (see
Table 1). After completion of the reaction (deter-
mined by TLC), the mixture was extracted with ace-
tone (2 × 10 mL) and the solid was filtrated. The
combined organic layers were dried over anhydrous
Na2SO4, concentrated in vacuo and purified by sil-
ica gel column chromatography using petroleum
ether/ethyl acetate (4:1) as eluent. The filtrated solid,
which was the recovered SA, was washed with ether
and activated in vacuo at 70◦C for 2 h prior to reuse.
3a: mp 134–136◦C (Lit. [12] 137–139◦C); FT-IR
(KBr) ν: 3294, 2964, 1633, 1594, 1475, 770 cm−1;
1H NMR (400 MHz, CDCl3) δ: 1.34 (s, 6H, 2×CH3),
2.23 (s, 2H, CH2), 2.37 (s, 3H, N C CH3), 2.97 (br,
s, 1H, NH), 6.71–6.74 (m, 1H, Ar H), 6.97–7.00 (m,
2H, Ar Hs), 7.13–7.15 (m, 1H, Ar H); EI-MS (70 eV)
m/z (%): 188 (M+, 100), 173 (44), 132 (21), 104 (64),
77 (32), 65 (27).
739 cm−1; H NMR (400 MHz, CDCl3) δ: 1.51–1.87
(m, 10H, CH2 ), 2.16–2.22 (m, 2H, CH2 ), 2.31–2.52
(m, 2H, N C CH2 ), 2.80–2.90 (m, 1H, N C CH),
6.65 (dd, J = 1.2, 8.0 Hz, 1H, Ar H), 6.82 (dt, J = 1.4,
7.2 Hz, 1H, Ar H), 6.95 (dt, J = 1.4, 7.2 Hz, 1H,
Ar H), 7.95 (dd, J = 1.2, 8.0 Hz, 1H, Ar H); EI-MS
(70 eV) m/z (%): 241 (M+ + 1, 100), 225 (60), 210
(10), 182 (11), 133 (15), 92 (6), 77 (5), 65 (13).
3e: mp 136–137◦C (Lit. [12] 137–139◦C); FT-IR
(KBr) ν: 3394, 3047, 2929, 2854, 1640, 1594, 1476,
1
754 cm−1; H NMR (400 MHz, CDCl3) δ: 1.25–1.84
(m, 16H, CH2 ), 2.31–2.35 (m, 1H, N C CH), 2.57
(t, J = 6.8 Hz, 2H, N C CH2), 3.75 (br, s, 1H, NH),
6.68 (dd, J = 1.4 Hz, J = 7.6 Hz, 1H, Ar H), 6.90–
6.98 (m, 2H, Ar Hs), 7.26 (dd, J = 1.4 Hz, J = 7.6 Hz,
1H, Ar H); EI-MS (70 eV) m/z (%): 267 (M+ – 1, 85),
237 (35), 223 (100), 210 (16), 195 (11), 91 (7), 77 (7),
65 (11).
3f: mp 146–148◦C (Lit. [12] 151–152◦C); FT-IR
(KBr) ν: 3280, 3057, 1633, 1600, 1467, 1329, 762,
1
749, 700, 688 cm−1; H NMR (400 MHz, CDCl3) δ:
Heteroatom Chemistry DOI 10.1002/hc

356 Xia and Lu
1.75 (s, 3H, CH3), 2.97 (d, J = 13.2 Hz, 1H, CHa2),
3.13 (d, J = 13.2 Hz, 1H, CHb2); 3.51 (s, 1H, NH),
6.85 (dd, J = 1.6 Hz, J = 8.0 Hz, 1H, Ar H), 7.05 (dt,
J = 1.6 Hz, J = 8.0 Hz, 2H, Ar Hs), 7.17–7.31 (m, 7H,
Ar Hs), 7.57 (dt, J = 1.6 Hz, J = 8.0 Hz, 4H, Ar Hs);
EI-MS (70 eV) m/z (%): 312 (M+, 10), 295 (100), 235
(25), 194 (30), 103 (20), 77 (60), 40 (80).
TABLE 1 Reaction Conditions in the Formation of Benzodi-
azepine 3a
Catalyst
Amount
(mol%)
Temp
(◦C)
Time
(h)
Yield
(%)
Entry Solvent
1
2
3
4
5
6
7
CH3CN
EtOH
CHCl3
No
No
No
20
20
20
5
10
20
No
Refluxing
Refluxing
Refluxing
r.t.
10
10
10
0.5
0.5
0.5
65
57
44
69
86
96
3g: mp 121–123◦C (Lit. [41] 117◦C); FT-IR (KBr)
ν: 3336, 3056, 2960, 1603, 1510, 1467, 1249, 1176,
1
1032, 832, 756 cm−1; H NMR (400 MHz, CDCl3) δ:
r.t.
r.t.
r.t.
1.73 (s, 3H, CH3), 2.93 (d, J = 13.2 Hz, 1H, CHa2),
3.06 (d, J = 13.2 Hz, 1H, CHb2), 3.45 (br, s, 1H, NH),
3.76 (s, 3H, OCH3), 3.80 (s, 3H, OCH3), 6.76–6.83 (m,
5H, Ar Hs), 7.05 (t, J = 8.8 Hz, 2H, Ar Hs), 7.33 (m,
1H, Ar H), 7.52 (d, J = 8.8 Hz, 2H, Ar Hs), 7.61 (d,
J = 8.8 Hz, 2H, Ar Hs); EI-MS (70 eV) m/z (%): 373
(M+ + 1, 6), 279 (9), 236 (100), 221 (35), 209 (11),
193 (13), 166 (17), 133 (16), 103 (15), 93 (7), 76 (14).
3h: mp 151–153◦C (Lit. [41] 154◦C); FT-IR (KBr)
ν: 3312, 3074, 1597, 1525, 1468, 1348, 855, 750,
694 cm−1; 1H NMR (400 MHz, CDCl3) δ: 1.84 (s,
3H, CH3), 3.01 (d, J = 13.6 Hz, 1H, CHa2), 3.31 (d,
J = 13.6 Hz, 1H, CHb2), 3.64 (br, s, 1H, NH), 6.90 (d,
J = 7.6 Hz, 1H, Ar H), 7.11 (t, J = 7.6 Hz, 1H, Ar H),
7.16 (t, J = 7.6 Hz, 1H, Ar H), 7.34 (d, J = 7.6 Hz,
1H, Ar H), 7.68 (d, J = 8.8 Hz, 2H, Ar Hs), 7.76
(d, J = 8.8 Hz, 2H, Ar Hs), 8.06 (d, J = 8.8 Hz, 4H,
Ar Hs); EI-MS (70 eV) m/z (%): 403 (M+ + 1, 5), 251
(100), 221 (40), 205 (24), 188 (15), 178 (21), 151 (11),
102 (13), 76 (23), 50 (27).
No
Overnight Trace
1 was recovered through column chromatography
when the condensation was carried out for 10 h. The
yield of the reaction increased remarkably, from 69%
to 96%, as the amount of SA was raised from 5 to
20 mol%, respectively. It seemed that 20 mol%
SA was sufficient to promote the reaction; higher
amounts of it could not obviously improve the yield.
However, in the absence of SA, the reaction could
hardly proceed even after long time (overnight).
Moreover, the recovery of the catalyst was also
tested. It is well known that SA is insoluble in many
organic solvents, especially the non-protonic and
low-polar ones. Therefore, in our case, it was ready
to separate SA from the acetone solution of products
by simple filtration. After activation through wash-
ing then heating at 70◦C for 2 h, the refreshed SA
could be reused in reaction with only a gradual de-
crease in its activity, the yields were 96%, 91%, 84%,
and 72%, respectively, over four runs.
RESULTS AND DISCUSSION
To survey the reaction conditions in the formation
of benzodiazepines assisted by SA, the condensation
of o-phenylenediamine (1) with acetone 2a was se-
lected as a model (Scheme 1) and the results were
indicated in Table 1.
Apparently, the efficiency and the yields of the
reaction in organic solution were much less than
those obtained under solvent-free conditions. In or-
ganic solutions, the conversion of 1 could not be
accomplished completely, a substantial amount of
Based on the above results, we extended our in-
vestigation to some other ketones (Scheme 2).
Aliphatic and aromatic ketones as well as cyclic
ones were screened as substrates to carry out the SA-
promoted synthesis of 1,5-benzodiazepine deriva-
tives. It was found that all ketones involved in reac-
tions could successfully undergo the condensations
assisted by 20 mol% SA to offer the expected prod-
ucts 3a–h in 33%–96% yields. Aliphatic and cyclic ke-
tones displayed their high reactivity, condensations
CH3
H
N
NH2
CH3
O
Sulfamic acid (cat.)
+
2
CH3
CH3
NH2
N
CH3
1
2a
3a
SCHEME 1
Heteroatom Chemistry DOI 10.1002/hc

Sulfamic Acid 357
R1
R2
R2
H
N
O
NH2
NH2
R2
20 mol% SA, solvent-free
r.t.–80oC, 0.5–3 h
+
2 R1
N
R1
1
2a–h
3a–h
SCHEME 2
involved with them could smoothly be accomplished
within 1 h in high yields under mild conditions
(Table 2). However, owing to the low activity of car-
bonyl groups, reactions participated with aromatic
ketones should be executed at 50–80◦C and the re-
action time was prolonged to 3 h (Table 2, entry
f, g, and h). The remarkable electron effect existed
in the reactions involving aromatic ketones, since
the one with an electron-withdrawing group like 4-
nitroacetophenone was able to fulfill the condensa-
tion in 81% yield, but the other one with an electron-
donating group like 4-methoxyacetophenone was
sluggish to carry out the condensation, afford-
ing the product 3g only in 33% yield, and the
TABLE 2 SA-promoted Synthesis of 1,5-Benzodiazepines 3a–h
Entry
Ketone
Product
Temp (◦C)
r.t.
Time (h)
0.5
Yield (%)∗
96
H
N
1
Acetone
3a
3b
N
H
N
2
2-Butanone
45
0.5
87
N
H
N
8
3b
N
H
N
3
3-Pentanone
45
0.5
90
3c
N
H
N
4
5
Cyclopentanone
Cyclohexanone
r.t.
r.t.
1
1
86
95
3d
3e
N
H
N
N
Ph
H
N
6
7
Acetophenone
50
80
2
3
86
33
3f
N
Ph
OCH3
H
N
4-Methoxyacetophenone
3g
N
OCH3
NO2
H
N
8
4-Nitroacetophenone
80
1.5
81
3h
N
NO2
∗Yield refers to the isolated pure products after column chromatography.
Heteroatom Chemistry DOI 10.1002/hc

358 Xia and Lu
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CONCLUSION
Herein we described
a
mild and effective
protocol for the solvent-free synthesis of
1,5-benzodiazepine derivatives through the conden-
sation of o-phenylenediamine and ketones using
sulfamic acid as a green and recyclable catalyst.
The simple procedure combined with the ease of
recovery and reuse of this novel catalyst made
our method very simple, convenient, and environ-
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