Efficient polymeric catalyst for one-pot synthesis of acenaphtho[1,2-b] pyrroles

Article abstract of DOI:10.1007/s11164-012-0939-5

Some new derivatives of acenaphtho[1,2-b]furans have been synthesized efficiently by one-pot reaction of (acenaphthylen-1-yloxy)trimethylsilane, various aldehydes, and isocyanides in the presence of silica-supported ionic liquid.

Full text of DOI:10.1007/s11164-012-0939-5

Res Chem Intermed
DOI 10.1007/s11164-012-0939-5
Efficient polymeric catalyst for one-pot synthesis
of acenaphtho[1,2-b]pyrroles
•
Mohammad Taghi Goldani Reza Sandaroos
Saman Damavandi
•
Received: 16 September 2012 / Accepted: 17 November 2012
Ó Springer Science+Business Media Dordrecht 2013
Abstract Some new derivatives of acenaphtho[1,2-b]furans have been synthesized
efficiently by one-pot reaction of (acenaphthylen-1-yloxy)trimethylsilane, various
aldehydes, and isocyanides in the presence of silica-supported ionic liquid.
Keywords One-pot synthesis Á Acenaphtho[1,2-b]furan Á
Silica-supported ionic liquid
Introduction
Fused furans are among the most important heterocyclic compounds with widespread
occurrence in nature [1, 2]. The pharmacological and biological activities of furan
derivatives have induced and encouraged a large number of research groups to
develop new synthetic approaches with the aim of obtaining more pharmacologically
and biologically effective compounds [3–5]. Among these various strategies,
isocyanide-based multicomponent reactions, introduced in the 1990s by Passerini [6],
have attracted specific attention [7–12]. Furthermore, ionic liquids have recently
become powerful alternatives to conventional molecular organic solvents due to
M. T. Goldani (&)
Department of Chemical Engineering, Birjand Branch, Islamic Azad University, Birjand, Iran
e-mail: mt.goldani@yahoo.com
R. Sandaroos (&)
Department of Chemistry, Faculty of Science, University of Birjand, Birjand, Iran
e-mail: r_sandaroos@yahoo.com
S. Damavandi
Department of Chemistry, Sarvestan Branch, Islamic Azad University, Sarvestan, Iran
123

M. T. Goldani et al.
some of their unique advantages such as undetectable vapor pressures and ability to
dissolve many organic and inorganic substances [13]. Additionally, ionic liquids are
readily recycled and tunable to specific chemical tasks. One type is Brønsted acidic
task-specific ionic liquids. Among ionic liquids, those possessing HSO-4 as a
counteranion have found broad applications in organic synthesis, acting as both
solvents and catalysts. Recently, immobilization processes of acidic ionic liquids
on solid supports have been designed [14–18]. Heterogenization of catalysts
and reagents can offer important advantages in handling, separation, and reuse
procedures.
In previous studies [19, 20], we reported catalyst-free synthesis of acenaph-
tho[1,2-b]furan compounds employing isocyanide, aldehyde, and silyl enol of
acenaphthylen-1(2H)-one. However, chemical yields were not sustainable. Accord-
ingly, in this study, we examined various ionic liquids to improve the efficiency of
our synthetic method. Among the ionic liquids used, supported ionic liquid d was
found to be the best choice and was used for synthesis of compounds 7a–k
(Scheme 1). In all cases, the efficiencies of catalyzed and noncatalyzed reactions
were compared (Table 1).
Experimental
Materials and methods
All products, except compounds 7h–k [19, 20], are new and were characterized by
infrared (IR), 1H nuclear magnetic resonance (NMR), 13C NMR, and elemental micro
1
analysis. H NMR spectra were recorded on a Bruker AQSAVANCE 400-MHz
spectrometer using tetramethylsilane (TMS) as internal standard (CDCl3 solution).
13C NMR spectra were recorded on a Bruker AQSAVANCE 100-MHz spectrometer
(CDCl3 solution). IR spectra were recorded from KBr disk on a Fourier-transform
(FT)-IR Bruker Tensor. Gas chromatography/mass spectroscopy (GC/MS) spectra
were recorded on an Agilent Technologies 6890 network GC system and an Agilent
5973 network mass-selective detector. Elemental analyses were performed using a
Heraeus CHN-O-Rapid analyzer. (Acenaphthylen-1-yloxy)trimethylsilane (1),
supported and unsupported ionic liquids were prepared according to the literature
[21, 22].
General procedure for preparation of acenaphtho[1,2-b]pyrrole derivatives
(7a–k)
To a magnetically stirred mixture of aldehyde (1 mmol) and catalyst (0.01 mmol)
in DMF (40 mL) at 0 °C was dropwise added a solution of (acenaphthylen-1-
yloxy)trimethylsilane (1) (1 mmol) in DMF (10 mL) over a 30-min period. Then,
the mixture was allowed to warm to room temperature and treated with a
solution of isocyanide (1.0 mmol) in DMF (10 mL). The mixture was refluxed for
10 h, cooled to room temperature, and filtered. The filtrate was extracted with
123

Efficient polymeric catalyst for one-pot synthesis
R1
NH
R2
O
O
TMS
DMF
O
catalysts a-d (0.01 eq)
R2CH
R1
+
+
C
N
reflux, 10h
7a-k
1
O
OMe
7c: R1
=
, R2
=
7b: R1
OMe
=
, R2 = p-NO2Ph
7a: R1
7d: R1
=
=
, R2
=
7f: R1
=
, R2 nPr
=
, R2 = H
Cl
7e: R1
=
, R2
=
NO2
OMe
7i: R1 = tBu , R2 = p-NO2Ph
7h: R1 = tBu, R2
=
OMe
7g: R1
=
, R2
=
Me
Me
Me
OMe
Cl
7k: R1
=
,R2 = p-NO2Ph
, R2
=
1
OMe
7j
: R
=
Me
Compounds 7a-k
N
N
HSO4
X
N
N
O
Si
O
OH
Si
O
O
OH
pmim
X
Si
Si
Si
O
O
O
pmim
(d):
HSO4-SiO2
X= (a): Cl; (b): BF3; (c): HSO4
Ionic liquids a-d
Scheme 1 Compounds 7a–k prepared in the presence of ionic liquids a–d
dichloromethane (4 9 15 mL). After evaporation of solvent, the residue was
washed with ether and crystallized from acetonitrile to give analytically pure
product (7a–k).
N-Cyclohexyl-9-(2,4-dimethoxyphenyl)acenaphtho[1,2-b]furan-8-amine (7a)
Brown powder (97 %); m.p. 195–200 °C; FT-IR (KBr) (mmax, cm-1): 3,355 (N–H),
1
1,230 (C–O), 1,200 (C–O); H NMR (400 MHz, CDCl3) dH 1.21–1.97 (10H, m,
5CH2), 3.52 (1H, m, N–CH), 3.75 (3H, s, OCH3), 3.81 (3H, s, –OCH3), 6.43 (1H,
bs, NH), 6.62–7.81 (9H, m, Ar–H); 13C NMR (100 MHz, CDCl3) dC 22.6, 28.7,
31.5, 49.6, 55.9, 56.2, 100.9, 107.1, 109, 117.8, 125.5, 127.3, 127.6, 128, 128.3, 129,
129.5, 133.5, 137.7, 139, 147.2, 158.4, 161.7; GC/MS: 425 (M?); Anal. Calcd. for
C28H27NO3: C, 79.03; H, 6.40; N, 3.29 %. Found: C, 78.84; H, 6.35; N, 3.23 %.
123

M. T. Goldani et al.
Table 1 Catalytic efficiencies of ionic liquids a–d for preparation of compound 7aa
Entry
Catalyst
Time (h)
Yield (%)b
1
2
3
4
5
6
a
–
10
10
10
10
10
10
39
97
76
67
64
51
[pmim]HSO4-SiO2
[pmim]HSO4
[pmim]BF4
[pmim]Cl
Silica support
Reaction conditions: 1.0 equiv. of silyl enol of acenaphthylen-1(2H)-one, 1.0 equiv. of 2,4-dime-
thoxybenzaldehyde, 1.0 equiv. of isocyanocyclohexane, 10 mol % of catalyst, 50 mL of DMF as solvent,
at refluxing condition
b
Isolated yields
N-Cyclohexyl-9-(4-nitrophenyl)acenaphtho[1,2-b]furan-8-amine (7b)
Brown powder (95 %); m.p. 209–214 °C; FT-IR (KBr) (mmax, cm-1): 3,281 (N–H),
1
1,541 (N–O), 1,360 (N–O); H NMR (400 MHz, CDCl3) dH 1.24–2.09 (10H, m,
5CH2), 3.60 (1H, m, N–CH), 4.92 (1H, bs, NH), 7.72–8.35 (10H, m, Ar–H); 13C
NMR (100 MHz, CDCl3) dC 24.5, 26.1, 30.5, 30.8, 33.2, 51.3, 110.7, 121.4, 125.1,
125.7, 127.6, 127.9, 129.1, 129.6, 130.3, 132.7, 135.1, 135.9, 137.4, 139.3, 141.5,
149.3, 154.8, 159.7, 175.4; GC/MS: 410 (M?); Anal. Calcd. for C26H22N2O3: C,
76.08; H, 5.40; N, 6.82 %. Found: C, 75.91; H, 5.34; N, 6.76 %.
(8-(Cyclohexylamino)acenaphtho[1,2-b]furan-9-yl)(phenyl)methanone (7c)
Brown powder (94 %); m.p. 181–184 °C; FT-IR (KBr) (mmax, cm-1): 3,350 (N–H),
1,690 (C=O); 1H NMR (400 MHz, CDCl3) dH 1.20–2.01 (10H, m, 5CH2), 3.53(1H, m,
N–CH), 6.16 (1H, bs, NH), 7.70–8.04 (11H, m, Ar–H); 13C NMR (100 MHz, CDCl3)
dC 20.6, 26.6, 33.9, 47.1, 109.7, 120.2, 124.3, 125.7, 127.2, 127.9, 128.1, 128.5, 129.5,
133.1, 133.7, 135.1, 139.2, 149.3, 151.8, 190.7; GC/MS: 393 (M?); Anal. Calcd. for
C27H23NO2: C, 82.42; H, 5.89; N, 3.56 %. Found: C, 82.30; H, 5.81; N, 3.52 %.
N-Cyclohexylacenaphtho[1,2-b]furan-8-amine (7d)
Brown powder (92 %); m.p. 161–163 °C; FT-IR (KBr) (mmax, cm-1): 3,364 (N–H);
1H NMR (400 MHz, CDCl3) dH 1.22–2.05 (10H, m, 5CH2), 3.51 (1H, m, N–CH),
4.76 (1H, s, =CH–), 6.09 (1H, bs, NH), 7.78–7.93 (6H, m, Ar–H); 13C NMR
(100 MHz, CDCl3) dC 24.3, 29.0, 33.6, 49.3, 104.8, 113.4, 127.3, 129.5, 129.9,
130.4, 131.7, 135.1, 138.9, 145.3, 150.2; GC/MS: 289 (M?); Anal. Calcd. for
C20H19NO: C, 83.01; H, 6.62; N, 4.84 %. Found: C, 82.95; H, 6.60; N, 4.81 %.
9-(2-Nitrostyryl)-N-cyclohexylacenaphtho[1,2-b]furan-8-amine (7e)
Brown powder (91 %); m.p. 189–192 °C; FT-IR (KBr) (mmax, cm-1): 3,363 (N–H),
1
1,535 (N–O), 1,354 (N–O); H NMR (400 MHz, CDCl3) dH 1.29–2.01 (10H, m,
123

Efficient polymeric catalyst for one-pot synthesis
5CH2), 3.53 (1H, m, N–CH), 6.05 (1H, bs, NH), 7.16 (1H, d, J = 12.4 Hz,
ArC=CH), 7.65–8.40 (11H, m, Ar–H and ArCH=C); 13C NMR (100 MHz, CDCl3)
dC 26.2, 31.6, 35.1, 53.3, 111.6, 124.6, 128.6, 129.1, 130.9, 131.6, 131.8, 132.2,
132.5, 133.1, 134.2, 137.6, 137.7, 139.3, 141.9, 143.2, 150.3, 151.7; GC/MS: 436
(M?); Anal. Calcd. for C28H24N2O3: C, 77.04; H, 5.54; N, 6.42 %. Found: C, 76.76;
H, 5.47; N, 6.35 %.
N-Cyclohexyl-9-propylacenaphtho[1,2-b]furan-8-amine (7f)
Brown powder (95 %); m.p. 174–176 °C; FT-IR (KBr) (mmax, cm-1): 3,360 (N–H);
1H NMR (400 MHz, CDCl3) dH 0.92 (3H, t, J = 7.8 Hz, CH3–C–C), 1.25–2.11
(10H, m, 5CH2), 1.85 (2H, m, C–CH2–C), 2.70 (2H, t, J = 7.8 Hz, C–CH2–C), 3.48
(1H, m, N–CH), 5.06 (1H, bs, NH), 7.69–7.92 (6H, m, Ar–H); 13C NMR (100 MHz,
CDCl3) dC 17.1, 20.3, 26.7, 28.6, 30.1, 33.6, 51.7, 113.1, 121.1, 127.6, 129.9, 131.7,
132.4, 132.4, 132.7, 137.3, 141.5, 141.8, 149.7; GC/MS: 331 (M?); Anal. Calcd. for
C23H25NO: C, 83.34; H, 7.60; N, 4.23; %. Found: C, 83.21; H, 7.54; N, 4.12 %.
9-(2,6-Dichlorophenyl)-N-cyclohexylacenaphtho[1,2-b]furan-8-amine (7g)
Brown powder (95 %); m.p. 182–186 °C; FT-IR (KBr) (mmax, cm-1): 3,359 (N–
1
H); H NMR (400 MHz, CDCl3) dH 1.22–2.00 (10H, m, 5CH2), 3.52 (1H, m, N–
CH), 6.22 (1H, bs, NH), 7.23–7.89 (9H, m, Ar–H); 13C NMR (100 MHz, CDCl3)
dC 25.5, 31.3, 34.4, 52.5, 113.9, 129.6, 131.4, 131.6, 131.7, 132.4, 132.4, 133.1,
134.8, 136.7, 136.9, 138.7, 140.9, 142.5; GC/MS: 433 (M?); Anal. Calcd. for
C26H21Cl2NO: C, 71.89; H, 4.87; N, 3.22 %. Found: C, 71.74; H, 4.81; N,
3.17 %.
N-tert-Butyl-9-(2,4-dimethoxyphenyl)acenaphtho[1,2-b]furan-8-amine (7h)
Brown powder (93 %); m.p. 135–138 °C; FT-IR (KBr) (mmax, cm-1): 3,364 (N–H),
1,210 (C–O), 1,200 (C–O); 1H NMR (400 MHz, CDCl3) dH 1.18 (9H, s, C(CH3)3),
3.70 (3H, s, OCH3), 3.74 (3H, s, –OCH3), 5.41 (1H, bs, NH), 6.59–7.71 (9H, m, Ar–
H); 13C NMR (100 MHz, CDCl3) dC 30.7, 51.3, 57.6, 57.9, 102.6, 108.8, 10.7,
119.5, 127.2, 129, 129.3, 129.7, 130.0, 130.7, 131.2, 135.2, 139.4, 140.7, 148.9,
160.1, 163.4; GC/MS: 399 (M?); Anal. Calcd. for C26H25NO3: C, 78.17; H, 6.31; N,
3.51 %. Found: C, 78.01; H, 6.24; N, 3.45 %.
N-tert-Butyl-9-(4-nitrophenyl)acenaphtho[1,2-b]furan-8-amine (7i)
Brown powder (78 %); m.p. 146–148 °C; FT-IR (KBr) (mmax, cm-1): 3,364 (N–H),
1,550 (N–O), 1,343 (N–O); 1H NMR (400 MHz, CDCl3) dH 1.17 (9H, s, C(CH3)3),
6.43 (1H, bs, NH), 7.76–8.30 (10H, m, Ar–H); 13C NMR (100 MHz, CDCl3) dC
31.8, 53.9, 113.1, 123.7, 127.5, 128.1, 130.0, 130.3, 131.5, 132, 132.7, 135.1, 137.5,
138.3, 139.8, 141.7, 143.9, 151.7, 157.2, 162.1, 177.8; GC/MS: 384 (M?); Anal.
Calcd. for C24H20N2O3: C, 74.98; H, 5.24; N, 7.29 %. Found: C, 74.71; H, 5.16; N,
7.19 %.
123

M. T. Goldani et al.
9-(2,4-Dimethoxyphenyl)-N-(2,6-dimethylphenyl)acenaphtho[1,2-b]furan-8-amine
(7j)
Brown powder (96 %); m.p. 163–167 °C; FT-IR (KBr) (mmax, cm-1): 3,451 (N–H),
1,130 (C–O), 1,200 (C–O); 1H NMR (400 MHz, CDCl3) dH 2.36 (6H, s, 2Me), 3.57
(3H, s, OCH3), 3.62 (3H, s, –OCH3), 6.74 (1H, bs, NH), 6.43–7.84 (12H, m, Ar–H);
13C NMR (100 MHz, CDCl3) dC 18.4, 58.7, 59.5, 104.7, 110.9, 112.8, 121.5, 121.6,
128.4, 129.8, 130.2, 130.5, 130.9, 131.2, 131.8, 133.9, 134.4, 138.4, 142.6, 142.6,
144.8, 152.1, 163.3, 166.6; GC/MS: 447 (M?); Anal. Calcd. for C30H25NO3: C,
80.51; H, 5.63; N, 3.13 %. Found: C, 80.46; H, 5.58; N, 3.02 %.
N-(2,6-Dimethylphenyl)-9-(4-nitrophenyl)acenaphtho[1,2-b]furan-8-amine (7k)
Brown powder (94 %); m.p. 142–144 °C; FT-IR (KBr) (mmax, cm-1): 3,237 (N–H),
1,501 (N–O), 1,418 (N–O); 1H NMR (400 MHz, CDCl3) dH 2.21 (6H, s, 2Me), 6.86
(1H, bs, NH), 7.52–8.27 (13H, m, Ar–H); 13C NMR (100 MHz, CDCl3) dC 22.4,
113.1, 122.7, 125.7, 129.6, 129.7, 130.5, 130.4, 130.7, 130.8, 131.9, 134.0, 134.1,
138.6, 142.2, 142.8, 145.2, 147.6, 152.3, 153.5; GC/MS: 432 (M?); Anal. Calcd. for
C28H20N2O3: C, 77.76; H, 4.66; N, 6.48 %. Found: C, 77.58; H, 4.43; N, 6.41 %.
Results and discussion
An equal stoichiometric ratio of silyl enol of acenaphthylen-1(2H)-one (1),
2,4-dimethoxybenzaldehyde, and isocyanocyclohexane and 10 mol % of ionic
liquid catalyst was used for the model reaction. To find the most efficient catalyst,
three ionic liquids: [pmim]Cl (1-propyl-3-methylimidazolium–Cl) (a), [pmim]BF4
(1-propyl-3-methylimidazolium–BF4) (b), and [pmim]HSO4 (1-propyl-3-methyli-
midazolium–HSO4) (c), possessing different counteranions (Scheme 1), were
comparatively used to catalyze the model reaction. As seen in Table 1, among the
ionic liquid catalysts (a–c) employed, [pmim]HSO4 showed the best catalytic
efficiency.
To investigate the effect of heterogenization on the catalytic behavior, the most
active catalyst, [pmim]HSO4 (c), was supported on modified silica to obtain the
immobilized catalyst [pmim]HSO4–SiO2 (d). Immobilization on silica support
enhanced the activity of the corresponding catalyst significantly (Table 1, entry 2).
The higher activity of the immobilized catalyst [pmim]HSO4–SiO2 (d) could be
attributed to the participation of SiO2 in the catalytic process. To support this
hypothesis, we used the silica support as catalyst under the same reaction conditions
and showed that it could improve the efficiencies of the reactions compared with the
noncatalyzed system (Table 1, compare entries 1 and 6). So, supported ionic liquid
d was used to assess the generality and scope of the reaction with respect to the
aldehyde and isocyanide components (Table 2). We examined various aliphatic
aldehydes, such as a,b-unsaturated aldehydes as well as substituted aromatic
aldehydes containing electron-withdrawing and electron-donating groups, and it
was determined that all of them were well tolerated, affording expected products in
123

Efficient polymeric catalyst for one-pot synthesis
good yields. In addition, we applied aliphatic and aromatic isocyanides, and found
that the reaction proceeded efficiently even with hindered aliphatic and aromatic
isocyanides (Table 2, entries 8–11). As can be seen, all chemical yields were
considerably improved in the presence of ionic liquid d, compared with those we
obtained under noncatalyzed conditions.
Table 2 Comparison of
Entry Compound Time (h)/yield (%)a,
catalyzed by catalyst d
Time (h)/yield
(%)a, not catalyzed
ionic-liquid-catalyzed and
noncatalyzed routes for
preparation of compounds
7a–k
1
7a
7b
7c
7d
7e
7f
10/97
10/95
10/94
10/92
10/91
10/95
10/92
10/95
10/93
10/96
10/94
10/44
10/50
10/40
10/39
10/37
10/40
10/40
10/42
10/44
10/34
10/36
2
3
4
5
6
7
7g
7h
7i
8
9
10
11
7j
7k
a
Isolated yields
C
N R
OTMS
C
N R
Me3SiC
N R
O
O
TMS
O
R'
H
R'CHO
(1)
NH
(3)
(2)
R
R
- TMSOH
R
N
N
C
4+1
Cycloaddition
R'
R'
O
O
H
O
R'
(6)
(7a-k)
(4)
R
N
Michael addition
R'
O
(5)
Scheme 2 Proposed mechanism for the one-pot three-component synthesis of compounds 7a–k
123

M. T. Goldani et al.
The effect of temperature was evaluated by carrying out the reaction at various
temperatures. The chemical yields increased as the reaction temperature was raised.
Hence, refluxing temperature was chosen as optimum temperature and applied for
all reactions. Various solvents such as CH2Cl2, CHCl3, ethanol, CH3CN, and
toluene were screened for the reaction, but DMF was found to be the best choice.
As established in our previous studies [19, 20], the first step of the mechanism
involves nucleophilic attack of the isocyanide onto silyl enol ether (1), breaking the
O–SiMe3 bond to generate an active enol ion pair complex (2). Reaction of the enol
with an aldehyde produces the aldol adduct (3), which, in turn, eliminates
(CH3)3SiOH to afford a,b-unsaturated ketone (4). Formation of the key iminolac-
tone intermediate (6) is achieved either via [4 ? 1] cycloaddition reaction or
Michael-type addition of the isocyanide with concomitant intermolecular cycliza-
tion. Benefiting from delocalization stability, the iminolactone (6) isomerizes to
form aminofuran heteroaromatic moiety (7) (Scheme 2).
Conclusions
One-pot three-component synthesis of some new derivatives of acenaphtho[1,2-b]
furans efficiently proceeded in the presence of supported ionic liquid catalyst
d. High chemical yields and short reaction times compared with those obtained in
our previous work establish the very important role of the supported ionic liquid
catalyst for one-pot synthesis of acenaphtho[1,2-b]furans.
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