Regioselective ring opening of 2,2-dicyanooxiranes by 1,3-dinucleophiles in the presence of Lewis acids such as bismuth(III) nitrate pentahydrate [Bi(NO3)3·5H2O] and zirconium(IV) chloride (ZrCl4)

Article abstract of DOI:10.1007/s11164-014-1560-6

Bismuth(III) nitrate pentahydrate [Bi(NO₃)₃·5H₂O] or zirconium(IV) chloride (ZrCl₄) has been shown to catalyze nucleophilic ring opening of 2,2-dicyanooxiranes along with ring closure by 1,3-dinucleophiles such

Full text of DOI:10.1007/s11164-014-1560-6

Res Chem Intermed
DOI 10.1007/s11164-014-1560-6
Regioselective ring opening of 2,2-dicyanooxiranes
by 1,3-dinucleophiles in the presence of Lewis acids
such as bismuth(III) nitrate pentahydrate
[Bi(NO3)3Á5H2O] and zirconium(IV) chloride (ZrCl4)
•
Mahboobeh Karbalaei Mohammad Seifi
Hassan Sheibani
•
Received: 29 December 2013 / Accepted: 8 February 2014
Ó The Author(s) 2014. This article is published with open access at Springerlink.com
Abstract Bismuth(III) nitrate pentahydrate [Bi(NO3)3Á5H2O] or zirconium(IV)
chloride (ZrCl4) has been shown to catalyze nucleophilic ring opening of 2,2-
dicyanooxiranes along with ring closure by 1,3-dinucleophiles such as 1H-1,3-
benzimidazole-2-thiol, 5-phenyl-4H-1,2,4-triazole-3-thiol, and thioureas. These
reactions led to efficient synthesis of heterocyclic compounds condensed with
benzimidazole or triazole derivatives. The used catalysts are inexpensive, highly
efficient, and reusable for opening of epoxides with 1,3-dinucleophiles at ambient
temperature, with excellent regioselectivity.
Keywords Bismuth(III) nitrate pentahydrate [Bi(NO3)3Á5H2O] Á
Zirconium(IV) chloride Á 1H-1,3-Benzimidazole-2-thiol Á 5-Phenyl-4H-1,2,4-
triazole-3-thiol Á Thioureas Á 2,2-Dicyanooxiranes
Introduction
2,2-Dicyanooxiranes and their a-haloketone derivatives are known as very effective
bielectrophile reagents for synthesis of a large variety of heterocyclic compounds
such as thiazoles [1], dithioles [2], imidazoles [3], 1,3-oxathioles [4], and condensed
imidazolo and thiazolo derivatives [5]. In general, nucleophilic reagents can react
with these compounds regioselectively: they can attack the oxirane ring, cyano
functional group to give either ring-opened products, new functionalized oxiranes or
different heterocycles. Epoxide ring opening with nucleophilic agents is an
important step in preparation of 1,2-disubstituted products [6]. Heating epoxides in
the presence of nucleophiles, which would occur with poorly nucleophilic addition,
suffers from lack of appreciable regioselectivity [6]. The requirement for high
M. Karbalaei Á M. Seifi Á H. Sheibani (&)
Department of Chemistry, Shahid Bahonar University of Kerman, 76169 Kerman, Iran
e-mail: hsheibani@mail.uk.ac.ir
123

M. Karbalaei et al.
temperature in epoxides sensitive to this condition led to the necessity for activation
of the epoxide rings to increase their susceptibility to nucleophilic attack. The
various methodologies developed for this purpose include the use of Lewis acid
catalysts such as alumina [7], metal triflates [8], transition-metal halides [9], alkali-
metal perchlorates [10], silica under high pressure [11], and montmorillonite clay
under microwave irradiation [12]. The search for new and efficient Lewis acid
catalysts for various useful organic transformations is one of the most important,
interesting, and challenging research topics in catalytic synthesis. On the other hand,
in recent years, economically affordable ecofriendly catalysts have received greater
acceptance for use in organic reactions. In this respect, bismuth(III) and
zirconium(IV) derivatives are known as Lewis acid catalysts in various organic
transformations involving carbon–carbon bond formation, protection-deprotection
chemistry, and conversion of epoxides into vic-acylamino hydroxy compounds [13–
16]. Since zirconium, in its normal quadrivalent state, displays no redox properties
but can attain a maximum covalency up to eight and displays low toxicity [16],
Zr(IV) compounds should be ideal for catalytic applications. Coordination of Bi3?
with the epoxide oxygen renders the epoxide susceptible to nucleophilic attack by
nucleophilic reagents. Considering the widespread applications of 2,2-dicyanoox-
iranes in synthesis of a large variety of heterocyclic compounds and their sensitivity
to high temperature, we planned to employ bismuth(III) nitrate pentahydrate and
zirconium(IV) chloride as Lewis acid catalysts to evaluate their catalytic efficiency
in carrying out ring-opening reactions of these epoxides with 1,3-dinucleophiles.
Results and discussion
We investigated ring opening and condensation reaction of 2,2-dicyanooxiranes
(1a–1d) with 1,3-dinucleophiles such as 1H-1,3-benzimidazole-2-thiol (2),
5-phenyl-4H-1,2,4-triazole-3-thiol (4), and thioureas (6a, 6b) in different conditions
at ambient temperature (Scheme 1). Lewis acid catalysts, namely bismuth(III)
nitrate pentahydrate and zirconium(IV) chloride, were used for activation of the
epoxide rings, rendering them more susceptible to nucleophilic attack under milder
conditions. Selective formation of the regioselective products 3, 5, and 7 arising
from nucleophilic attack at the benzylic carbon (Cb) of 2,2-dicyanooxiranes (1a-1d)
was observed in the course of the reactions with 1,3-dinucleophiles 2, 4, and 6.
Reactions of 2,2-dicyanooxiranes with 1,3-dinucleophiles occur at ambient
temperature in the absence of catalyst in long experimental times [17–19]. These
epoxides are sensitive to high temperature; therefore, we planned to employ Lewis
acid catalysts bismuth(III) nitrate pentahydrate and zirconium(IV) chloride to
decrease the activation energy of the ring-opening reaction of epoxides with 1,3-
dinucleophiles (Table 1).
To determine standard operating conditions for these reactions, we used some
polar and nonpolar solvents in the reaction of 3-phenyloxirane-2,2-dicarbonitrile
(1a) and 1H-benzo[d]imidazole-2-thiol (2) in the presence of Lewis acid catalysts
bismuth(III) nitrate pentahydrate and zirconium(IV) chloride as model reactions to
123

Regioselective ring opening of 2,2-dicyanooxiranes by 1,3-dinucleophiles
Scheme 1 Condensation reaction of 2,2-dicyanooxiranes (1a–1d) with 1,3-dinucleophiles such as 1H-
1,3-benzimidazole-2-thiol (2), 5-phenyl-4H-1,2,4-triazole-3-thiol (4), and thioureas (6a, 6b)
Table 1 Reaction of 1,3-dinucleophiles (2, 4, 6a, 6b) with 2,2-dicyanooxiranes (1a–1d) for synthesis of
3a–3d, 5a, 5b, 7a, and 7b in the presence of Bi(NO3)3Á5H2O (5 mol.%) and ZrCl4 (10 mol.%)
Compd. Oxirane Dinuc. Without catalyst
Bi(NO3)3 (5 mol.%)
ZrCl4 (10 mol.%)
Time (h) Yield (%) Time (min) Yield (%) Time (min) Yield (%)
3a
3b
3c
3d
5a
5b
7a
7b
1a
1b
1c
1d
1b
1d
1d
1d
2
2
7
7
90
93
94
90
90
94
68
70
40
35
35
40
30
35
70
75
90
92
95
93
92
94
83
88
30
25
25
35
25
30
60
70
92
94
95
94
92
94
85
90
2
7
2
7
4
7
4
7
6a
6b
24
24
investigate the effects of solvent for preparing compound 3a. In each case, the
substrates were mixed together with 10 mol.% of these catalysts agitated with
10 mL solvent at room temperature. The results are presented in Table 2. It is
123

M. Karbalaei et al.
noteworthy that polar solvents such as acetonitrile afforded better yields than
nonpolar solvents.
We also optimized the quantity of catalysts. The best results were obtained when
the reactions were carried out in the presence of 5 or 10 mol.% bismuth(III) nitrate
pentahydrate and zirconium(IV) chloride, respectively. The results are presented in
Table 3.
We also attempted to reuse the catalysts by a variety of methods (Table 4). Direct
reuse of the catalysts (Table 4, entry 2, 6) led to a greater than 15 % decrease in
activity, while washing with dichloromethane and ethylacetate prior to reuse also
resulted in lower conversions (Table 4, entry 3, 4, 7, 8). This phenomenon probably
arose because the reactant and product were not completely desorbed from the
catalyst, and therefore the active sites were blocked.
Using this protocol (Scheme 1), we investigated reactions of 2,2-dicyanooxiranes
1, which have three electron-deficient centers, with 1,3-dinucleophiles for synthesis
of heterocyclic compounds in the presence of Lewis acid catalysts Bi(NO3)3Á5H2O
(5 mol.%) and ZrCl4 (10 mol.%). In these reactions, the 1,3-dinucleophiles act
Table 2 Solvent effects on ring-opening reaction of epoxide 1a with 1H-benzo[d]imidazole-2-thiol (2)
Entry
Solvent
Catalyst
Time (min)
Yield (%)
1
2
3
4
5
6
8
9
Toluene
Toluene
THF
Bi(NO3)3Á5H2O
ZrCl4
80
70
48
37
40
30
45
35
75
78
87
89
90
92
88
91
Bi(NO3)3Á5H2O
ZrCl4
THF
CH3CN
CH3CN
Ethanol
Ethanol
Bi(NO3)3Á5H2O
ZrCl4
Bi(NO3)3Á5H2O
ZrCl4
THF tetrahydrofuran
Table 3 Optimized quantity of catalysts for ring-opening reaction of epoxide 1a in synthesis of com-
pound 3a
Entry
Catalyst
Mol.% catalyst
Time (min)
Yield (%)
1
2
Bi(NO3)3Á5H2O
ZrCl4
3
50
38
45
35
40
30
40
30
40
30
85
88
87
89
90
92
90
92
90
92
5
3
Bi(NO3)3Á5H2O
ZrCl4
4
4
7.5
5
5
Bi(NO3)3Á5H2O
ZrCl4
6
10
6
7
Bi(NO3)3Á5H2O
ZrCl4
8
12.5
7
9
Bi(NO3)3Á5H2O
ZrCl4
10
15
123

Regioselective ring opening of 2,2-dicyanooxiranes by 1,3-dinucleophiles
Table 4 Reusability of Bi(NO3)3Á5H2O and ZrCl4 in ring-opening reaction of epoxide 1a for synthesis of
compound 3a
Entry
Catalyst
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
a
Bi(NO3)3Á5H2O (1st use)
Bi(NO3)3Á5H2Oa (2nd use)
Bi(NO3)3Á5H2Ob (2nd use)
Bi(NO3)3Á5H2Oc (2nd use)
ZrCl4 (1st use)
ZrCla4 (2nd use)
ZrClb4 (2nd use)
40
70
55
55
30
55
40
40
90
75
83
81
92
78
85
84
ZrClc4 (2nd use)
Direct reuse of catalysts
b
c
Bi(NO3)3Á5H2O and ZrCl4 were washed with dichloromethane
Bi(NO3)3Á5H2O and ZrCl4 were washed with ethylacetate
Scheme 2 A reasonable mechanism for formation of product 3
regioselectively on Cb and Ca of 2,2-dicyanooxiranes 1, which have three electron-
deficient centers. These processes are highly regioselective, with the products
resulting from initial attack of the nucleophilic sulfur atom of compounds 2, 4 or 6
on Cb of 2,2-dicyanooxiranes 1 followed by ring opening. The intermediate I was
formed by loss of cyano group. The last step is intramolecular nucleophilic addition
of nitrogen on carbonyl group of intermediate I, followed by elimination of HCN to
form a single product. Coordination of the Lewis acids with the epoxide and
carbonyl group oxygen increases the polarity of the C–O bond and makes the
adjacent carbons more susceptible to nucleophilic attack (Scheme 2).
Conclusions
Bismuth(III) nitrate pentahydrate and zirconium(IV) chloride are known as effective
Lewis acid catalysts for synthesis of heterocyclic compounds which condensed
[1,3]thiazole with benzimidazole, triazole or thiazolinone derivatives via nucleo-
philic reaction of 1,3-dinucleophiles with 2,2-dicyanooxiranes at ambient temper-
ature. These catalysts show an environmentally friendly character and are
inexpensive and easily obtained. Moreover, the procedure offers several advantages
including high yield, operational simplicity, clean reaction conditions, and short
123

M. Karbalaei et al.
reaction time, making it a useful and attractive process for synthesis of these
compounds.
Experimental
General procedures
Melting points were measured on an Electrothermal Engineering Ltd. apparatus and
are uncorrected. Infrared (IR) spectra were measured on a Mattson 1000 FT-IR
spectrometer. Proton and carbon nuclear magnetic resonance (NMR) spectra were
recorded with a Bruker DRX-400 AVANCE spectrometer at 400 and 100 MHz,
respectively. Mass spectra were recorded on a MS-QP2000A Shimadzu mass
spectrometer operating at an ionization potential of 70 eV. Elemental analyses were
performed using a Heraeus CHN-O-Rapid analyzer. 2,2-Dicyanooxiranes 1a–1d
were prepared according to a literature procedure [18].
Procedure for preparation of 2-arylidene-[1,3]thiazolo[3,2-a]benzimidazol-3(2H)-
ones (3a–3d), 5-substituted thiazolo[3,2-b][1,2,4]triazol-6-ones (5a, 5b),
and thiazolinones (7a, 7b)
A mixture of 2,2-dicyanooxiranes 1a–1d (2 mmol), 1H-benzo[d]imidazole-2-thiol 2
or 5-mercapto-3-phenyl-s-triazole 4 or thioureas (6a, 6b) (2 mmol), and ZrCl4
(10 mol.%) or Bi(NO3)3Á5H2O (5 mol.%) in CH3CN (20 mL) was stirred for the
appropriate time (Table 1), the progress of the reaction being monitored by thin-
layer chromatography (TLC) using hexane/ethylacetate as eluent. When the reaction
was completed as indicated by TLC, the crude product 3a–3d, 5a, 5b, 7a, and 7b
was precipitated from the reaction mixture, and the solid was filtered and
recrystallized with hexane/ethylacetate to get pure product.
2-Phenyl[1,3]thiazolo[3,2-a]benzimidazol-3(2H)-one (3a) White crystals; m.p.
190–192 °C. IR (KBr, mmax/cm-1): 1,742 (C=O), 1,603 (C=N). 1H NMR
3
(400 MHz, DMSO-d6): 8.81 (d, 1H, JH–H = 8 Hz, CH), 7.71 (d, 1H,
3JH–H = 8 Hz, CH), 7.67–7.39 (m, 7H, Ar), 6.40 (s, 1H). 13C NMR (100 MHz,
DMSO-d6): 153.84 (C=O), 144.75 (C=N), 142.92, 133.21, 132.69, 132.38, 129.45,
129.04, 128.93, 124.63, 122.87, 117.76, 50.10 (C2). MS (m/z): 266 (M?(98), 237
(80), 205 (20), 150 (15), 121 (100), 90 (78), 77 (40). Anal. calcd. for C15H10N2OS:
C, 67.65; H, 3.78; N, 10.52 %. Found: C, 67.42; H, 3.66; N, 10.18 %.
2-(4-Chlorophenyl)[1,3]thiazolo[3,2-a]benzimidazol-3(2H)-one (3b) White crys-
tals; m.p. 136–139 °C. IR (KBr, mmax/cm-1): 1,726 (C=O), 1,609 (C=N). 1H NMR
(400 MHz, DMSO-d6): 7.87 (d, 1H, JH–H = 8 Hz, CH), 7.66 (d, 1H,
3
3
3JH–H = 8 Hz, CH), 7.62 (d, 2H, JH–H = 8.8 Hz, CH), 7.50 (d, 2H,
3
3
3JH–H = 8.8 Hz, CH), 7.42 (t, 1H, JH–H = 8 Hz, CH), 7.35 (d, 1H, JH–H = 8 Hz,
CH), 6.32 (s, 1H). 13C NMR (100 MHz, DMSO-d6): 166.83 (C=O), 156.88 (C=N),
123

Regioselective ring opening of 2,2-dicyanooxiranes by 1,3-dinucleophiles
149.42, 133.61, 133.44, 131.17, 128.72, 128.02, 125.77, 123.74, 123.35, 118.70,
67.32 (C2). MS (m/z): 300 (M?) (100), 27 (70), 237 (50), 156 (80), 124 (20), 89
(73), 63 (40). Anal. calcd. for C15H9ClN2OS: C, 59.90; H, 3.02; N, 9.31 %. Found:
C, 59.83; H, 2.88; N, 9.01 %.
2-(4-Nitrophenyl)[1,3]thiazolo[3,2-a]benzimidazol-3(2H)-one (3c) White crystals;
1
m.p. 193–196 °C. IR (KBr, mmax/cm-1): 1,750 (C=O), 1,609 (C=N). H NMR
(400 MHz, DMSO-d6): 8.49 (d, 2H, 3JH–H = 8 Hz, CH), 7.72 (d, 1H, 3JH–H = 8 Hz,
CH), 7.50–7.26 (m, 5H, Ar), 5.79 (s, 1H). 13C NMR (100 MHz, DMSO-d6): 165.83
(C=O), 153.20 (C=N), 150.3, 145.4, 140.01, 138.5, 129.73, 126.56, 124.55, 124.49,
119.51, 128.9, 57.61 (C2). MS (m/z): 311 (M?) (100), 282 (20), 265 (15), 236 (40), 167
(98), 151 (20), 145 (50), 121 (30), 109 (20), 90 (77), 77 (80), 63 (88). Anal. calcd. for
C15H9N3O3S: C, 57.87; H, 2.91; N, 13.50 %. Found: C, 57.69; H, 2.85; N, 13.21 %.
2-(2,5-Dimethoxyphenyl)[1,3]thiazolo[3,2-a]benzimidazol-3(2H)-one (3d) Yellow
1
crystals; m.p. 140–143 °C. IR (KBr, mmax/cm-1): 1,748 (C=O), 1,611 (C=N). H
3
NMR (400 MHz, DMSO-d6): 7.81 (d, 1H, JH–H = 8 Hz, CH), 7.49 (d, 1H,
3JH–H = 8 Hz, CH), 7.31–7.12 (m, 2H, CH), 7.05 (s, 1H, CH), 7.02 (d, 1H,
3JH–H = 8 Hz, CH), 6.88 (d, 1H, 3JH–H = 8 Hz, CH), 6.01 (s, 1H), 3.65, 3.48 (s, 6H,
2OCH3). 13C NMR (100 MHz, DMSO-d6): 167.91 (C=O), 154.70 (C=N), 152.59,
150.56, 126.40, 124.75, 124.38, 123.38, 119.61, 117.79, 116.30, 56.88, 56.09
(2OCH3) 57.61 (C2). MS (m/z): 326 (M?) (100), 311 (85), 267 (20), 178 (15), 163 (50),
149 (60), 135 (20), 121 (40), 107 (12), 91 (30), 77 (43), 63 (35). Anal. calcd. for
C17H14N2O3S: C, 62.56; H, 4.32; N, 8.58 %. Found: C, 62.44; H, 4.28; N, 8.31 %.
5-(4-Chlorophenyl)-2-phenylthiazolo[3,2-b][1,2,4]triazol-6(5H)-one (5a) White crystals;
1
m.p. 152–155 °C. IR (KBr, mmax/cm-1): 1,744 (C=O), 1,692, 1,611 (C=N). H
NMR (400 MHz, DMSO-d6): 8.13–8.11 (m, 2H, Ar), 7.64 (d, 2H, JH–H = 8 Hz,
3
3
CH), 7.57–7.53 (m, 3H, Ar), 7.50 (d, 2H, JH–H = 8 Hz, CH), 6.41 (s, 1H). 13C
NMR (100 MHz, DMSO-d6): 169.73 (C=O), 165.03, 163.96 (C=N), 134.00,
132.56, 131.35, 131.27, 129.15, 129.04, 128.97, 126.90, 58.17 (C5). MS (m/z): 327
(M?) (80), 301 (12), 281 (12), 264 (55), 177 (20), 152 (60), 125 (40), 103 (100), 89
(85), 77 (30). Anal. calcd. for C16H10ClN3OS: C, 58.63; H, 3.07; N, 12.28 %.
Found: C, 58.44; H, 2.98; N, 11.97 %.
5-(2,5-Dimethoxyphenyl)-2-phenylthiazolo[3,2-b][1,2,4]triazol-6(5H)-one (5b)
Orange crystals; m.p. 204–206 °C. IR (KBr, mmax/cm-1): 1,754 (C=O), 1,606
3
(C=N). 1H NMR (400 MHz, DMSO-d6): 8.13 (d, 2H, JH–H = 8 Hz, CH),
7.70–7.66 (m, 3H, Ar), 7.20 (s, 1H, CH), 7.05–7.00 (m, 2H, CH), 6.31 (s, 1H),
3.76, 3.67 (s, 6H, 2OCH3). 13C NMR (100 MHz, DMSO-d6): 169.09 (C=O),
164.73, 164.32 (C=N), 153.08, 151.17, 131.19, 129.10, 129.05, 126.88, 122.58,
117.28, 115.78, 56.45, 55.84 (2OCH3), 55.67 (C5). MS (m/z): 353 (M?) (12), 294
(7), 178 (30), 163 (95), 147 (20), 135 (23), 121 (15), 103 (100), 92 (18), 77 (28).
Anal. calcd. for C18H15N3O3S: C, 61.18; H, 4.28; N, 11.89 %. Found: C, 60.95; H,
4.15; N, 11.60 %.
123

M. Karbalaei et al.
2-Amino-5-(2,5-dimethoxyphenyl)thiazol-4(5H)-one (7a) Yellow crystals; m.p.
195–196 °C. IR (KBr, mmax/cm-1): 3,316 (NH2), 1,692 (C=O). 1H NMR
(400 MHz, DMSO-d6): 8.92 (s, 2H, NH2), 7.28 (d, 1H, JH–H = 8 Hz, CH), 7.15
3
3
(d, 1H, JH–H = 8 Hz, CH), 6.98 (s, 1H, CH), 5.91 (s, 1H, CH), 3.72, 3.65 (s, 6H,
2OCH3). 13C NMR (100 MHz, DMSO-d6): 176.25 (C=O), 169.24 (C=N), 153.33,
150.28, 127.48, 116.15, 114.36, 113.56, 56.25, 55.68 (2OCH3), 54.94 (C5). MS (m/
z): 252 (M?) (16), 221 (15), 190 (38), 137 (58), 115 (100), 74 (25). Anal. calcd. for
C11H12N2O3S: C, 52.37; H, 4.79; N, 11.10 %. Found: C, 52.18; H, 4.39; N,
10.98 %.
5-(2,5-Dimethoxyphenyl)-2-(phenylamino)thiazol-4(5H)-one (7b) White crystals;
m.p. 218–220 °C. IR (KBr, mmax/cm-1): 3,303 (NH), 1,702 (C=O). 1H NMR
(400 MHz, DMSO-d6): 9.12 (s, 1H, NH), 7.38 (d, 1H, 3JH–H = 8 Hz, CH), 7.27 (d,
1H, 3JH–H = 8 Hz, CH), 7.23–7.02 (m, 5H, Ar), 6.89 (s, 1H, CH), 5.78 (s, 1H, CH),
3.76, 3.69 (s, 6H, 2OCH3). 13C NMR (100 MHz, DMSO-d6): 173.63 (C=O), 168.23
(C=N), 153.03, 151.10, 134.32, 128.69, 128.45, 127.65, 124.85, 116.87, 114.16,
113.24, 56.45, 55.63 (2OCH3), 54.86 (C5). MS (m/z): 328 (M?) (10), 297 (26), 266
(16), 251 (58), 191 (12), 189 (26), 137 (34), 77 (100). Anal. calcd. for
C17H16N2O3S: C, 62.18; H, 4.91; N, 8.53 %. Found: C, 61.97; H, 4.48; N, 8.12 %.
Acknowledgments The authors express appreciation to the Shahid Bahonar University of Kerman
Faculty Research Committee for its support of this investigation.
Open Access This article is distributed under the terms of the Creative Commons Attribution License
which permits any use, distribution, and reproduction in any medium, provided the original author(s) and
the source are credited.
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