Three-component passerini-smiles coupling reaction of aldehydes and isocyanides with tropolone catalyzed by silica nanoparticles

Article abstract of DOI:10.3906/kim-1111-20

The use of Smiles rearrangement in Passerini-type couplings with tropolone allows very straightforward multicomponent formation of a-aryloxy amide derivatives. The 3-component addition of isocyanide to tropolone (2-hydroxy-2,4,6-cycloheptatrien-1-one) and aldehyde in the presence of silica nanoparticles (silica NP, ca. 70 nm) proceeds easily in methanol to form the title compounds in a new Passerini-Smiles-type reaction. TUeBITAK.

Full text of DOI:10.3906/kim-1111-20

Turk J Chem
36 (2012) , 537 – 544.
¨
˙
c
ꢀ TUBITAK
doi:10.3906/kim-1111-20
Three-component Passerini-Smiles coupling reaction of
aldehydes and isocyanides with tropolone catalyzed by
silica nanoparticles
Abdolhossain MASSOUDI1, Issa AMINI1, Ali RAMAZANI2,∗ and
Fatemeh ZEINALI NASRABADI3
1Department of Chemistry, Payame Noor University, P.O. Box 19395-3697, Tehran-IRAN
2Department of Chemistry, Zanjan Branch, Islamic Azad University,
P.O. Box 49195-467, Zanjan-IRAN
e-mail: aliramazani@gmail.com
3Department of Chemistry, University of Zanjan, P. O. Box 45195-313, Zanjan-IRAN
Received: 10.11.2011
The use of Smiles rearrangement in Passerini-type couplings with tropolone allows very straightforward
multicomponent formation of α-aryloxy amide derivatives. The 3-component addition of isocyanide to
tropolone (2-hydroxy-2,4,6-cycloheptatrien-1-one) and aldehyde in the presence of silica nanoparticles (silica
NP, ca. 70 nm) proceeds easily in methanol to form the title compounds in a new Passerini-Smiles-type
reaction.
Key Words: Smiles rearrangement, Passerini-type coupling, tropolone, isocyanide, silica nanoparticles,
Passerini-Smiles-type reaction
Introduction
Multicomponent reactions allow more than 2 facile and flexible building blocks to be combined in practical,
timesaving 1-pot operations. Due to their valued features such as atom economy, various starting materials
and products, inherent simple experimental procedures, and their 1-pot character, they are perfectly suited for
automated synthesis.1 Therefore, MCRs have attracted much attention because of their exceptional synthetic
applications.2−7 Since all the organic reactants employed are used and moved toward the target compound
the purification of products resulting from MCRs is simple.8,9 Isocyanide-based multicomponent reactions
∗Corresponding author
537

Three-component Passerini-Smiles coupling reaction of aldehydes and..., A. MASSOUDI, et al.
(abbreviated to IMCRs by Ugi and D¨omling) have an interesting position. The special features of IMCRs,
including unique synthetic potential, convergent nature, high atom economy, ease of implementation, and
the generation of molecular diversity, are considered as acceptable factors in the relative efficiency of the
reactions.9−17
In recent years, nanoparticles (NPs) have attracted tremendous attention in catalysis because of their
improved efficiency under mild and environmentally benign conditions in the context of ecological (green)
synthesis.18,19 Due to their enormously large and highly reactive surface area, NPs have potential to exhibit
superior catalytic activity in comparison to their bulk counterparts.20,21
Recently, we have established a 1-pot method for the preparation of organic compounds.22−25 As part
of our ongoing program to develop efficient and robust methods for the synthesis of heteroatom-containing
compounds,26−34 we report the preparation of a new class of α-aryloxy amide derivatives 4a-g by a novel
3-component condensation reaction of aldehydes 1, isocyanides 2, and tropolone 3 in the presence of silica NPs
in excellent yields (Scheme 1).
OH
O
O
H
O
o
MeOH
60 C
HN
R2
R2 NC
+
+
R1
SiO2 NP, 24 h
R1
O
O
4
1
2
3
Scheme 1. Three-component synthesis of α-aryloxy amide derivatives 4 in the presence of silica nanoparticles (see
Table 1).
Table 1. SiO2 nanoparticle (NP)-promoted synthesis of α-aryloxy amide derivatives 4.a
4
a
b
c
d
e
f
R1
H
R2
Yield (%)b
Cyclohexyl
tert-Butyl
Cyclohexyl
tert-Butyl
Cyclohexyl
82
79
81
78
8
H
n-Butyl
Ethyl
3-Nitrophenyl
3-Formylphenyl Cyclohexyl
Ethyl Cyclohexyl
78
8
g
a See Scheme 1; 0.3 g SiO2 NP/mmol reactants were applied. b Yield of isolated 4.
Experimental
Starting materials and solvents were obtained from Merck (Germany) and Fluka (Switzerland) and were used
without further purification. The methods were used to follow the reactions were TLC and NMR. TLC and NMR
538

Three-component Passerini-Smiles coupling reaction of aldehydes and..., A. MASSOUDI, et al.
indicated that there was no side product. IR spectra were measured on a Jasco 6300 FTIR spectrometer. 1 H-
and 13 C-NMR spectra (CDCl3) were recorded on a BRUKER DRX-250 AVANCE spectrometer at 400.22 and
100.63 MHz, respectively. Elemental analyses were performed using a Heraeus CHN-O-Rapid analyzer. Mass
spectra were recorded on a FINNIGAN-MATT 8430 mass spectrometer operating at an ionization potential of
70 eV. Preparative thin layer chromatography was prepared from Merck silica gel powder.
General procedure for the preparation of compounds 4
Silica NPs (0.3 g) were added to a mixture of aldehyde (1 mmol), tropolone (1 mmol), and isocyanide (1 mmol)
in 7 mL of CH3 OH at 60 ◦ C, followed by reflux for 24 h. Silica NPs were isolated from the reaction mixture by
simple filtration and washed with methanol (3 mL). The solvent was removed under reduced pressure and the
viscous residue was purified by preparative thin layer chromatography (silica gel; petroleum ether–ethyl acetate
(2:1)). The solvent was removed under reduced pressure and the products (4a-g) were obtained.
N1 -cyclohexyl-2-[(7-oxo-1,3,5-cycloheptatrienyl) oxy]acetamide (4a)
White crystal, (yield: 82%), Rf = 0.20 (petroleum ether/ethyl acetate 2:1), mp 96-98 ◦ C. IR (neat): v = 3479,
.
2939, 1635, 1620, 1595, 1289, 1194, 1091, 773 cm−1 1 H-NMR (400 MHz, CDCl3) δ (ppm): 1.10-2.20 (m, 10H,
5 CH2 of cyclohexyl), 3.80-4.00 (m, 1H, CH–N), 4.54 (s, 2H, OCH2), 6.80 (d, 1H, CH of tropone, J = 9.6 Hz),
6.98 (t, 1H, CH of tropone, J = 9.0 Hz), 7.10 (t, 1H, CH of tropone, J = 10.2 Hz), 7.25-7.50 (m, 3H, CH of
tropone and NH). 13 C-NMR (100 MHz, CDCl3) δ (ppm): 24.75, 25.44, 32.75 (3 CH2 of cyclohexyl), 48.04 (CH
of cyclohexyl), 68.63 (OCH2), 116.27, 129.78, 132.55, 137.15, 137.91 (5 CH of tropone), 163.57 (C of tropone),
165.96 (C=O of amide), 180.61 (C=O of tropone). Analysis of C15 H19 NO3 (261.32). (% calculation/found):
C: 68.94/68.91, H: 7.33/7.38, N: 5.36/5.32. MS, m/z(%): 261(2), 163 (46), 140 (9), 136 (100), 135 (95), 123
(15), 107 (44), 106 (28), 105 (38), 90 (10), 83 (28), 77 (44), 65 (15), 58 (20), 55 (31), 41 (27).
N1 -(tert-butyl)-2-[(7-oxo-1,3,5-cycloheptatrienyl) oxy]acetamide (4b)
White crystal, (yield: 79%). Rf = 0.23 (petroleum ether/ethyl acetate 2:1), mp 75-76 ◦ C. IR (neat): v =
.
3420, 2982, 1670, 1621, 1594, 1282, 1198, 1089, 775 cm−1 1 H-NMR (400 MHz, CDCl3) δ (ppm): 1.44 (s, 9H,
CMe3), 4.45 (s, 2H, OCH2), 6.79 (d, 1H, CH of tropone, J = 9.6 Hz), 6.98 (t, 1H, CH of tropone, J = 9.0 Hz),
7.10 (t, 1H, CH of tropone, J = 10.2 Hz), 7.20-7.40 (m, 3H, CH of tropone and NH). 13 C-NMR (100 MHz,
CDCl3) δ (ppm): 28.68 (CMe3), 51.41 (CMe3), 68.73 (CH2), 116.06, 129.65, 132.51, 137.07, 137.86 (5 CH of
tropone), 163.53 (C of tropone), 166.03 (C=O of amide), 180.54 (C=O of tropone). Analysis of C13 H17 NO3
(235.28). (% calculation/found): C: 66.36/66.39, H: 7.28/7.26, N: 5.95/5.94. MS, m/z(%): 235 (4), 163 (62),
136 (100), 135 (91), 123 (21), 113 (15) 107 (55), 106 (29), 105 (48), 90 (15), 77 (46), 65 (20), 58 (49), 57 (57),
41 (37).
N1 -cyclohexyl-2-[(7-oxo-1,3,5-cycloheptatrienyl) oxy]hexanamide (4c)
Yellow oil, (yield: 81%). Rf = 0.26 (petroleum ether/ethyl acetate 2:1), IR (neat): v = 3480, 2935, 1657, 1639,
1595, 1283, 1192, 1080, 778 cm−1
.
1 H-NMR (400 MHz, CDCl3) δ (ppm): 0.92 (t, 3H, CH3 , J = 7.2 Hz),
539

Three-component Passerini-Smiles coupling reaction of aldehydes and..., A. MASSOUDI, et al.
1.10-2.20 (m, 16H, 5 CH2 of cyclohexyl and 3 CH2 of acyclic), 3.70-3.80 (m,1H, CH–N), 4.61 (t, 1H, H-C, J =
5.8 Hz), 6.81 (d, 1H, CH of tropone, J = 9.6 Hz), 6.88 (t, 1H, CH of tropone, J = 10.0 Hz), 7.06 (t, 1H, CH
of tropone, J = 10.0 Hz), 6.90-7.60 (m, 3H, CH of tropone and NH). 13 C-NMR (100 MHz, CDCl3) δ (ppm):
13.94 (CH3), 22.48 (CH2 of acyclic), 24.77, 25.42, 27.82, 32.60, 32.84 (5 C H2 of cyclohexyl and acyclic), 47.98
(CH of cyclohexyl), 82.39 (CH); 118.28, 130.03, 132.62, 137.09, 138.03 (5CH of tropone), 164.47 (C of tropone),
169.50 (C=O of amide), 181.42 (C=O of tropone). Analysis of C19 H27 NO3 (317.42). (% calculation/found):
C: 71.89/71.84, H: 8.57/8.59, N: 4.41/4.44. MS, m/z(%): 318 (100), 317 (13), 219 (94), 196 (52), 191 (36), 122
(31), 114 (27), 107 (44), 106 (30), 105 (20), 94 (23), 83 (37), 77 (18), 65 (18), 55 (66), 41 (53).
N1 -(tert-butyl)-2-[(7-oxo-1,3,5-cycloheptatrienyl)oxy]butanamide (4d)
Yellow oil, (yield: 78%). Rf = 0.27 (petroleum ether/ethyl acetate 2:1), IR (neat): v = 3483, 2937, 1673, 1648,
.
1594, 1281, 1194, 1083, 780 cm−1 1 H-NMR (400 MHz, CDCl3) δ (ppm): 1.08 (t, 3H, CH3 , J = 7.2 Hz), 1.37
(s, 9H, CMe3), 2.00-2.20 (m, 2H, CH2), 4.40 (t, 1H, H-C, J = 5.4 Hz), 6.88 (d, 1H, CH of tropone, J = 9.6
Hz), 7.08 (t, 1H, CH of tropone, J = 10.0 Hz), 6.94-7.50 (m, 4H, CH of tropone and NH). 13 C-NMR (100 MHz,
CDCl3) δ (ppm): 9.26 (CH3), 25.77 (CH2); 28.61 (CMe3), 51.17 (CMe3), 82.98 (C H), 117.90, 129.86, 132.57,
136.99, 137.96 (5 CH of tropone), 164.37 (C of tropone), 169.41 (C=O of amide), 181.30 (C=O of tropone).
Analysis of C15 H21 NO3 (263.33). (% calculation/found): C: 68.42/68.40, H: 8.04/8.01, N: 5.32/5.37.
N1 -cyclohexyl-2-(3-nitrophenyl)-2-[(7-oxo-1,3,5-cycloheptatrienyl) oxy]acetamide
(4e)
White crystal, (yield: 80 %). Rf = 0.26 (petroleum ether/ethyl acetate 2:1), mp 125-126 ◦ C. IR (neat): v =
3265, 2927, 1660, 1657, 1627, 1595, 1592, 1530, 1284, 1193, 1082, 774 cm−1
.
1 H-NMR (400 MHz, CDCl3)
δ (ppm): 1.20-2.10 (m, 10H, 5 CH2 of cyclohexyl), 3.70-3.80 (m, 1H, CH–N), 5.58 (s, 1H, OCH), 6.78 (d,
1H, CH of tropone, J = 10.0 Hz), 6.94-7.35 (m, 4H, CH of tropone), 7.60 (t, 1H, CH of arom, J = 8.0 Hz),
7.93-8.30 (m, 3H, CH of arom and NH), 8.45 (s, 1H, CH of arom). 13 C-NMR (100 MHz, CDCl3) δ (ppm):
24.65, 25.43, 32.67 (3 CH2 of cyclohexyl), 48.44 (CH of cyclohexyl), 81.08 (CH), 119.43, 121.74, 123.75, 129.77,
130.93, 132.25, 132.74, 137.28, 138.61 (9 CH of tropone and arom), 138.00 (C, arom), 148.43 (C, C-NO2),
163.10 (C of tropone), 166.65 (C=O of amide), 181.03 (C=O of tropone). Analysis of C21 H22 N2 O5 (382.41).
(% calculation/found): C: 65.96/65.91, H: 5.80/5.82, N: 7.33/7.36.
N1 -cyclohexyl-2-(3-formylphenyl)-2-[(7-oxo-1,3,5-cycloheptatrienyl)oxy]acetamide
(4f)
Yellow oil, (yield: 78%). Rf = 0.36 (petroleum ether/ethyl acetate 2:1), IR (neat): v = 3267, 2930, 2851,
1710, 1661, 1650,1621, 1594, 1282, 1191, 1080, 777 cm−1
.
1 H-NMR (400 MHz, CDCl3) δ (ppm): 1.20-2.10
(m, 10H, 5 CH2 of cyclohexyl), 3.70-3.80 (m, 1H, CH–N of cyclohexyl), 5.57 (s, 1H, OCH), 6.76 (d, 1H, CH of
tropone, J = 10.4 Hz), 7.76-7.35 (m, 4H, CH of tropone), 7.60 (t, 1H, CH of arom, J = 7.60 Hz), 7.85-7.97
(m, 3H, CH of arom and NH), 8.04 (s, 1H, CH of arom), 10.06 (s, 1H, CH of ArCOH). 13 C-NMR (100 MHz,
CDCl3) δ (ppm): 24.66, 25.46, 32.65 (3 CH2 of cyclohexyl), 48.32 (CH of cyclohexyl), 81.38 (CH); 118.73,
128.13, 129.57, 129.76, 130.47, 132.33, 132.51, 137.17, 138.39 (9 CH of tropone and arom), 136.77 (C, arom),
540

Three-component Passerini-Smiles coupling reaction of aldehydes and..., A. MASSOUDI, et al.
137.03 (C, C-NO2), 163.17 (C of tropone), 167.06 (C=O of amide), 181.01 (C=O of tropone), 191.90 (C=O of
ArCOH). Analysis of C22 H23 NO4 (365.42). (% calculation/found): C: 72.31/72.35, H: 6.34/6.36, N: 3.83/3.85.
N1 -cyclohexyl-2-[(7-oxo-1,3,5-cycloheptatrienyl)oxy]butanamide (4g)
White crystal, (yield: 80%), Rf = 0.37 (petroleum ether/ethyl acetate 2:1), mp 94-95 ◦ C. IR (neat): v = 3491,
.
2933, 1655, 1642, 1597, 1280, 1193, 1082, 767 cm−1 1 H-NMR (400 MHz, CDCl3) δ (ppm): 9.41 (t, 3H, CH3 ,
J = 7.4 Hz), 1.10-2.20 (m, 12H, 5 CH2 of cyclohexyl and CH2 of acyclic), 3.70-3.80 (m, 1H, CH–N); 4.59 (t,
1H, H-C, J = 5.4 Hz), 6.88 (d, 1H, CH of tropone, J = 9.6 Hz), 7.06 (t, 1H, CH of tropone, J = 10.0 Hz),
6.90-7.60 (m, 4H, CH of tropone and NH). 13 C-NMR (100 MHz, CDCl3) δ (ppm): 9.41 (CH3), 24.75, 25.43,
25.99, 32.64, (4 CH2 of cyclohexyl and acyclic), 47.98 (CH of cyclohexyl), 83.12 (CH), 118.33, 130.03, 132.57,
137.04, 138.06 (5 CH of tropone), 164.48 (C of tropone), 169.25 (C=O of amide), 181.42 (C=O of tropone).
Analysis of C17 H23 NO3 (289.37). (% calculation/found): C: 70.56/70.53, H: 8.01/8.02, N: 4.84/4.86.
Results and discussion
The aldehyde 1 was trapped by the isocyanide 2 and tropolone 3 in the presence of silica NPs in methanol at 60
◦ C over 24 h, leading to the formation of α-aryloxy amide derivatives 4 (Scheme 1 and Table 1). The reaction
proceeded smoothly and cleanly under mild and neutral conditions and no side reactions were observed.
Silica NPs were prepared from silica gel HF254 residues. The morphology and grain size of the silica NPs
were investigated by SEM (Figure 1).33
Figure 1. SEM of the synthesized silica nanoparticles.
Silica NPs were found to catalyze the synthesis of α-aryloxy amide derivatives from aldehydes 1, iso-
cyanides 2, and tropolone 3 in methanol at 60◦ C with high efficiency (Scheme 1 and Table 1). We also used
silica gel powder (Merck) instead of silica NPs in this reaction, but increasing reaction times and decreasing
α-aryloxy amide yields were observed (Scheme 1 and Table 1). The use of just 0.3 g of silica NPs per mmol of
reactants is sufficient to push the reaction forward. Higher amounts of silica NP (0.4 g) did not improve the
result to a great extent (Table 2, entries 4-7).
541

Three-component Passerini-Smiles coupling reaction of aldehydes and..., A. MASSOUDI, et al.
Table 2. Synthesis of α-aryloxy amide 4a from the reaction of formaldehyde, cyclohexylisocyanide, and tropolone
under various conditions.
Entry Catalysta or solvent
Temp (◦C) Time (h) Yield (%)b
1
2
3
4
5
6
7
MeOH
60
90
90
60
60
60
60
72
72
72
48
24
24
24
35
27
25
67
70
82
82
H2O
neat
MeOH/Silica gel powder (Merck) (1 g)
MeOH/SiO2 NP (0.1 g)
MeOH/SiO2 NP (0.3 g)
MeOH/SiO2 NP (0.4 g)
a Amount of SiO2 catalyst per mmol of reactants. b Yields of isolated 4a.
In order to investigate the effects of other reaction media in this reaction, we carried out the described
condensation in MeOH, H2 O, and solvent-free (neat) systems (Table 2, entries 1-3).
The structures of the products were deduced from their IR, 1 H-NMR, and 13 C-NMR spectra, and mass
spectrometry. The characterization data of the compounds are given below.
The 1 H-NMR spectrum of 4a consisted of several multiplets for the cyclohexyl (δ = 1.10-2.20 ppm)
moieties, a multiplet for the NCH (δ = 3.80-4.00 ppm) of cyclohexyl moiety, a singlet for the OCH2 (δ =
4.54 ppm) of the acyclic part, a doublet for the tropolone hydrogen (δ = 6.80 ppm,J = 9.6 Hz), a triplet for
the tropolone hydrogen (δ = 6.98 ppm, J = 9.0 Hz), a triplet for the tropolone hydrogen (δ = 7.10 ppm, J
= 10.2 Hz), and a multiplet for a tropolone hydrogen and NH (δ = 7.25-7.50 ppm). The 1 H-decoupled 13 C-
NMR spectrum of 4a showed 13 distinct signals. Partial assignment of these signals is given in the experimental
section. The 1 H- and 13 C-NMR spectra of compounds 4b-g were similar to those of 4a, except for the aromatic
or aliphatic moieties, which exhibited characteristic signals with appropriate chemical shifts.
A mechanistic pathway for this reaction is provided in Scheme 2. On the basis of the chemistry of
isocyanides, it is reasonable to assume that the first step may involve nucleophilic addition of the isocyanide
2 to aldehyde 1, which is facilitated by its protonation with the tropolone 3, leading to nitrilium intermediate
6. This intermediate may be attacked by the conjugate base of the tropolone 3 to form 1:1:1 adduct 7. The
intermediate 7 may undergo Smiles rearrangement to afford the isolated α-aryloxy amide derivatives 4 via
intermediate 8.
It may be speculated that the polar amphoteric surface (hydroxyl groups of the silica NP) facilitates the
interaction of adsorbed weak acidic and basic components due to stabilization of the corresponding transition
states and intermediates by H-bonding. This interaction with the neighboring silanol groups is shown in Scheme
2 for the first reaction step. Participation of 2 proximate silanol groups (one as a H-bond donor and the other
as a H-bond acceptor) in the reaction mechanism also seems plausible.
542

Three-component Passerini-Smiles coupling reaction of aldehydes and..., A. MASSOUDI, et al.
R2
N+ C–
H
OH
O
H
H
O
R1
1
2
3
+
+
O
OH
O
5
H
R1
H
R2
N
R1
R2
N+
O
C
H
O
R1
HO
R2
HO
HO
N
6
O
4
O
O
O
7
8
Scheme 2. Proposed mechanism for the formation of α-aryloxy amide derivatives 4 in the presence of silica nanopar-
ticles.
Conclusions
The reported method offers a mild, simple, and efficient route for the preparation of α-aryloxy amide derivatives
4 from aldehydes 1, isocyanides 2, and tropolone 3 in the presence of silica NPs. Its ease of work-up, high
yields, and fairly mild reaction conditions make it a useful addition to modern synthetic methodologies. Other
aspects of this process are under investigation.
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