Montmorillonite K10: An efficient catalyst for solvent-free synthesis of 1,5-benzodiazepine derivatives

Article abstract of DOI:10.1080/00397910701873243

2,3-Dihydro-1H-1,5-benzodiazepines have been synthesized under solvent-free conditions in good yields from o-phenylenediamine and ketones catalyzed by montmorillonite K10. This method has advantages of mild reaction conditions, simple operation, and envir

Full text of DOI:10.1080/00397910701873243

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Montmorillonite K10: An Efficient Catalyst for
Solvent‐Free Synthesis of 1,5‐Benzodiazepine
Derivatives
Li‐Tao An a , Fei‐Qing Ding a , Jian‐Ping Zou a & Xiao‐Hua Lu a
a Key Laboratory of Organic Synthesis of Jiangsu Province , College of
Chemistry and Chemical Engineering, Suzhou University , Suzhou, Jiangsu,
China
Published online: 17 Apr 2008.
To cite this article: Li‐Tao An , Fei‐Qing Ding , Jian‐Ping Zou & Xiao‐Hua Lu (2008) Montmorillonite K10: An
Efficient Catalyst for Solvent‐Free Synthesis of 1,5‐Benzodiazepine Derivatives, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 38:8, 1259-1267, DOI:
10.1080/00397910701873243
To link to this article: http://dx.doi.org/10.1080/00397910701873243
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Synthetic Communicationsw, 38: 1259–1267, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701873243
Montmorillonite K10: An Efficient Catalyst
for Solvent-Free Synthesis
of 1,5-Benzodiazepine Derivatives
Li-Tao An, Fei-Qing Ding, Jian-Ping Zou, and Xiao-Hua Lu
Key Laboratory of Organic Synthesis of Jiangsu Province, College of
Chemistry and Chemical Engineering, Suzhou University, Suzhou,
Jiangsu, China
Abstract: 2,3-Dihydro-1H-1,5-benzodiazepines have been synthesized under solvent-
free conditions in good yields from o-phenylenediamine and ketones catalyzed by
montmorillonite K10. This method has advantages of mild reaction conditions,
simple operation, and environmental friendliness.
Keywords: 1,5-Benzodiazepine, montmorillonite K10, neat reaction, solid acid,
solvent-free reaction
INTRODUCTION
1,5-Benzodiazepine derivatives have received significant attention because of
their accessibility, easy functionalization, and potential pharmacological prop-
erties including anti-inflammatory, antianxiety, anticonvulsant, and hypnotic
activities.[1] It represents a “privileged scaffold” found in compounds active
against a variety of target types including peptide hormones,[2a] interleukin
converting enzymes,[2b] and inhibitors of mitochondrial F1F0 adenosine tri-
phosphate (ATP) hydrolase.[2c] More recently, the area of biological interest
in 1,5-benzodiazepines has been extended to various diseases such as
Received February 13, 2007
Address correspondence to Jian-Ping Zou, Key Laboratory of Organic Synthesis of
Jiangsu Province, College of Chemistry and Chemical Engineering, Suzhou Univer-
sity, Hengyi Street, Suzhou 215123, Jiangsu, China. E-mail: wuyanhong@pub.sz.
jsinfo.net
1259

1260
L.-T. An et al.
cancer,[3a] viral infection,[3b] and cardiovascular disorders.[3c,d] These deriva-
tives are also used as dyes for acrylic fibers in the photography industry.[4]
Because of their wide range of pharmacological activity and industrial and
synthetic applications, the synthesis of 1,5-benzodiazepines has received
increasing attention. Usually, they are prepared from the condensation of
o-phenylenediamines with a,b-unsaturated carbonyl compounds, b-haloke-
tones, or ketones catalyzed by BF3-OEt2,[5] polyphosphoric acid,[6] CeCl3-
NaI/SiO2,[7] I2,[8] ZnCl2,[9] SmI2,[10] YbCl3,[11] and cerium ammonium
nitrate (CAN).[12] However, many of them suffer from the drawbacks such
as high temperature, drastic conditions, relatively expensive reagents, and
nonenvironmental friendliness except for some methods,[13] so there is
scope to explore a new, mild, efficient, and green procedure for the
synthesis of 1,5-benzodiazepines. We report here a solvent-free and facile
method for the synthesis of 1,5-benzodiazepines in the presence of montmor-
illonite K10 at room temperature.
Recently, considerable attention has been devoted to heterogeneous
organic transformations utilizing inorganic solid acids.[14a,b] The most
obvious merit of heterogeneous catalysis is reducing the use of organic
solvent.[14c] Meanwhile, organic synthesis under solvent-free conditions is
of great interest in view of growing environmental awareness.[14d,e] Clay is
a class of inorganic solid acids, which are cheap and have special catalytic
activities for organic reactions under heterogeneous reaction conditions.[15a,b]
Montmorillonite K10 is one of the most important inorganic solid acids, which
has been extensively reported to promote acid-dependent reactions[15c–f] and
as carrier of catalyst.[16] However, to our knowledge, there is no report on the
synthesis of 1,5-benzodiazepines catalyzed by montmorillonite K10.
RESULTS AND DISCUSSION
At the initial step, o-phenylenediamine (1.0 mmol), acetone (2.5 mmol), and
montmorillonite K10 (0.30 g) were mixed at ambient temperature; the corre-
sponding 1,5-benzodiazepine was produced in good yield in 6 h (Scheme 1)
without any by-product detected by thin-layer chromatography (TLC)
analysis. Encouraged by the result, the reaction was extended to other
ketones (Scheme 2), and the expected 1,5-benzodiazepines were obtained in
good to excellent yields (Table 1). As shown in Table 1, the acetophenones
Scheme 1.

Montmorillonite K10
1261
Scheme 2. 3a, R1 ¼ C6H5, R2 ¼ H; 3b, R1 ¼ CH3, R2 ¼ H; 3c, R1 ¼ p-Cl-C6H4,
R2 ¼ H; 3d, R1 ¼ p-NO2-C6H4, R2 ¼ H; 3e, R1 ¼ p-CH3-C6H4, R2 ¼ H; 3f,
R1 ¼ m-NO2-C6H4; 3g, R1 ¼ CH3CH2, R2 ¼ H; and 3h, R1 þ R2 ¼ C4H8.
gave good yields (83–90%), whereas 3-pentanone and cyclohexanone gave
moderate yields (75% and 64%, respectively). The structures of all products
were confirmed by comparison of their spectral data and the literature
reported. Furthermore, X-ray analysis of compound 3c was carried out
(Fig. 1). From the packing diagram, it is obvious that there is a hydrogen
bond -N-H. . .N- between molecules, which formed a chain in the cell unit.
To our knowledge, this is the first report of the single-crystal structure of 3c.
In conclusion, we have developed a practical, clean procedure for the
synthesis of 2,3-dihydro-1H-1,5-benzodiazepines at room temperature in the
presence of montmorillonite K10. The advantages of the present protocol
are mild conditions and easy workup. Furthermore, the catalyst is environmen-
tally friendly and inexpensive.
EXPERIMENTAL
Melting points are uncorrected. 1H NMR and 13C NMR spectra were recorded
on a Varian Inova-400 spectrometer, and trimethyl silane (TMS) was used as
internal standard. Mass spectra were taken on a Micromass spectrometer.
Elemental analyses were carried out on a Carlo Erba EA 1110-CHNOS
instrument.
General Procedure for the Synthesis of 1,5-Benzodiazepine
Acetone (0.15 g, 2.5 mmol) was added to a mixture of phenylenediamine
(0.11 g, 1.0 mmol) and montmorillonite K10 (0.30 g). They stood still for
the appropriate time. When the reaction was complete (monitored by TLC,
ethyl acetate–petroleum ether (1:4, v/v) as eluent), 5 mL of acetone was
added and filtered; the filtrate was evaporated to dryness. The residue was
subjected to column chromatography over silica gel using petroleum ether–
acetone (4:1) as eluent to afford pure 3b (0.17 g). The recovered catalyst
was washed by acetone (3 ꢀ 5 mL), activated by keeping in the oven for
2 h at 120 8C, and directly used in the next experiments.

1262
L.-T. An et al.
Table 1. Synthesis of 1,5-benzodiazepines catalyzed by K10
Time Yielda
Entry
1
Ketone
Product
Number
(h)
(%)
3a
24
90
2
3
3b
3c
6
90
87
24
4
3d
24
85
5
3e
24
90
6
7
3f
24
24
83
75
3g
(continued)

Montmorillonite K10
1263
Table 1. Continued
Time Yielda
Entry
8
Ketone
Product
Number
(h)
(%)
3h
10
64
aIsolated yield.
Spectral Data of Products
2,2-Dimethyl-4-phenyl-2,3-dihydro-1H-1,5-benzodiazepine (3a): Mp 150–
152 8C (lit.[9] 150–152 8C). 1H NMR (CDCl3, 400 MHz): d 6.83–7.60
(m, 14H, ArH), 3.52 (s, 1H, NH), 2.96–3.15 (d, 2H, J ¼ 13.2 Hz), 1.76
(s, 3H, CH3). 13C NMR (CDCl3, 100 MHz): d 168.2 (C55N), 148.0, 140.5,
139.9, 130.2, 128.8, 128.5, 127.5, 126.7, 125.9, 122.1, 121.9, 74.2, 43.5, 30.3.
2,2,4-Trimethyl-2,3-dihydro-1H-1,5-benzodiazepine (3b): Mp 136–138 8C
(lit.[9] 137–138 8C). 1H NMR (CDCl3, 400 MHz): d 7.12–7.14 (m, 1H, ArH),
6.96–7.01 (m, 2H, ArH), 6.72–6.74 (m, 1H, ArH), 2.97 (s, 1H, NH), 2.37
(s, 3H, CH3), 2.22 (s, 2H, CH2), 1.34 (s, 6H, 2CH3). 13C NMR (CDCl3,
100 MHz): d 173.1 (C55N), 141.1, 138.3, 127.1, 125.9, 122.5, 122.2, 68.9,
45.4, 30.8, 30.2.
4-(4-Chlorophenyl)-2,2-dimethyl-2,3-dihydro-1H-1,5-benzodiazepine (3c):
Mp 147–149 8C (lit.[17] 143–144 8C). 1H NMR (CDCl3, 400 MHz): d 6.84–7.53
Figure 1. X-ray analysis of compound 3c.

1264
L.-T. An et al.
(m, 12H, ArH), 3.43 (s, 1H, NH), 2.87–3.09 (dd, 2H, J1 ¼ 12 Hz, J2 ¼ 12.8 Hz),
1.74 (s, 3H, CH3).
2,2-Dimethyl-4-(4-nitrophenyl)-2,3-dihydro-1H-1,5-benzodiazepine (3d):
Mp 154–155 8C (lit.[12] 156–158 8C). 1H NMR (CDCl3, 400 MHz): d
6.90–8.08 (m, 12H, ArH), 3.64 (s, 1H, NH), 2.99–3.32 (m, 2H, CH2), 1.85
(s, 3H, CH3). C22H18N4O4 (402.13) calcd.: C, 65.66; H, 4.51; N, 13.92.
Found: C, 65.37; H, 4.47; N, 14.01.
2,2-Dimethyl-4-p-tolyl-2,3-dihydro-1H-1,5-benzodiazepine (3e): Mp 99–
101 8C (lit.[12] 98–99 8C). 1H NMR (CDCl3, 400 MHz): d 6.81–7.59
(m, 12H, ArH), 3.52 (s, 1H, NH), 2.96–3.11 (m, 2H, CH2), 2.34 (s, 3H,
CH3), 2.31 (s, 3H, CH3), 1.74 (s, 3H, CH3). 13C NMR (CDCl3, 100 MHz):
d 168.1 (C55N), 145.5, 140.8, 140.5, 138.7, 137.4, 137.2, 129.5, 129.3,
129.0, 127.6, 126.6, 125.7, 122.1, 122.0, 73.9, 43.3, 30.3, 21.8, 21.4.
2,2-Dimethyl-4-(3-nitrophenyl)-2,3-dihydro-1H-1,5-benzodiazepine (3f):
Mp 164–166 8C (lit.[17] 151–153 8C). 1H NMR (CDCl3, 400 MHz): d
6.92–8.48 (m, 12H, ArH), 3.56 (s, 1H, NH), 2.99–3.28 (m, 2H, CH2), 1.87
(s, 3H, CH3). 13C NMR (CDCl3, 100 MHz): d 164.6 (C55N), 149.6, 148.7,
141.0, 139.8, 137.6, 133.0, 132.4, 130.0, 129.7, 129.4, 127.9, 124.9, 122.9,
122.7, 122.0, 121.3, 104.0, 74.6, 43.3, 37.6, 30.4. HRMS (m/z): calcd. for
C22H18N4O4 402.1328; found 402.1295.
2,2,4-Triethyl-3-methyl-2,3-dihydro-1H-1,5-benzodiazepine (3g): Mp
1
140–141 8C (lit.[8b] 142–144 8C). H NMR (CDCl3, 400 MHz): d 6.59–
7.34 (m, 4H, ArH), 3.85 (s, 1H, NH), 2.81–2.83 (m, 1H), 2.49–2.57
(m, 2H), 1.52–1.56 (m, 2H), 1.20–1.37 (m, 4H), 0.68–0.96 (m, 10H).
10-Spirocyclohexane-2,3,4,10,11,11a-hexahydro-1H-dibenzo[b,e][1,4]
1
diazepine (3h): Mp 134–136 8C. (lit.[8b] 137–139 8C). H NMR (CDCl3,
400 MHz): d 6.99–7.33 (m, 4H, ArH), 3.80 (br, 1H, NH), 2.87–3.24
(m, 3H), 1.55–2.75 (m, 16H). HRMS (m/z): calcd. C18H24N2 268.1939,
found 268.1929.
Crystallographic Data for 3c
Crystals from acetone-petroleum, C22H18Cl2N2, Mr ¼ 381.28, monoclinic, space
˚
group P21/c, a ¼ 14.095(3), b ¼ 9.9845(15), c ¼ 14.859(3) A, b ¼ 116.728(3)8,
3
V ¼ 1867.7(6) A , Z ¼ 4, Dc ¼ 1.356 g cm23, m(MoKa) ¼ 0.355 mm21
.
˚
F(000) ¼ 792, T ¼ 213(2) K, crystal dimensions: 0.48 ꢀ 0.38 ꢀ 0.20 mm3,
˚
Rigaku Mercury CCD, MoKa radiation, l ¼ 0.71070 A, umax ¼ 25.358, 17639
measured reflections: 3404 unique, 3103 with I . 2s(I). The final refinement
converged to R ¼ 0.0432 and wR ¼ 0.0940. X-ray data has been deposited at
the Cambridge Crystallographic Data Center, deposition number CCDC
621740. Copies of the data can be obtained free of charge on application to

Montmorillonite K10
1265
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: (þ44) 1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk).
ACKNOWLEDGMENTS
We thank the Key Laboratory of Organic Synthesis of Jiangsu Province and
Suzhou Scientific Committee for financial support (JSK016 and SG 0219).
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