An efficient and green method for the synthesis of Betti base employing nano-SiO2–H3BO3 as a novel recyclable heterogeneous catalyst

Article abstract of DOI:10.1007/s11164-017-3024-2

Abstract: In this research, nano-SiO₂–H₃BO₃ is introduced as a novel environmentally benign and recyclable heterogeneous catalyst for the synthesis of aminonaphthols under solvent-free conditions without an additional co-catalyst or additive in air. This synthesis method offers several advantages, such as a green and eco-friendly protocol, operational simplicity, mild reaction conditions, short reaction times, higher yields and easy work-up procedures. The work-up of these very clean reactions involves only recrystallization of the product from ethanol and recovery of the catalyst by filtration. The catalyst can be reused several times without losing activity.

Full text of DOI:10.1007/s11164-017-3024-2

Res Chem Intermed
DOI 10.1007/s11164-017-3024-2
An efficient and green method for the synthesis of Betti
base employing nano-SiO2–H3BO3 as a novel recyclable
heterogeneous catalyst
Reza Teimuri-Mofrad1 Mahdi Gholamhosseini-Nazari1
•
•
Somayeh Esmati1 Aziz Shahrisa1
•
Received: 12 December 2016 / Accepted: 26 June 2017
Ó Springer Science+Business Media B.V. 2017
Abstract In this research, nano-SiO2–H3BO3 is introduced as a novel environmentally
benign and recyclable heterogeneous catalyst for the synthesis of aminonaphthols under
solvent-free conditions without an additional co-catalyst or additive in air. This synthesis
method offers several advantages, such as a green and eco-friendly protocol, operational
simplicity, mild reaction conditions, short reaction times, higher yields and easy work-up
procedures. The work-up of these very clean reactions involves only recrystallization of
the product from ethanol and recovery of the catalyst by filtration. The catalyst can be
reused several times without losing activity.
Graphical Abstract
Keywords Betti reaction Á Nanocatalyst Á Boric acid Á Recyclability Á Solvent-free
Electronic supplementary material The online version of this article (doi:10.1007/s11164-017-3024-2)
contains supplementary material, which is available to authorized users.
&
Reza Teimuri-Mofrad
teymouri@tabrizu.ac.ir
1
Department of Organic and Biochemistry, Faculty of Chemistry, University of Tabriz,
P.O. Box 51666-16471, Tabriz, Iran
123

R. Teimuri-Mofrad et al.
Introduction
One of the important reactions in the field of multicomponent synthesis is the Betti
reaction which was discovered at the beginning of the twentieth century by Mario
Betti [1]. This reaction is an important aminoalkylation reaction with a carbon–
carbon bond and a carbon–nitrogen bond which are formed at the same time. In fact,
Betti’s reaction, which synthesized a-aminobenzilnaphthol, is a modified Mannich
reaction, in which 2-naphthol, benzaldehyde and amine derivatives react together
[2]. Compounds which are synthesized by the Betti reaction, are known as Betti
bases. Due to the several interesting biological [3–5], synthetic [6–12] and catalytic
[8, 13, 14] applications of Betti bases, synthesis of substituted Betti base derivatives
have become an important area of synthetic chemistry. After a long gap since Betti’s
report, Katritzky et al. [15] reported the synthesis of aminoalkylphenols by
benzotriazole methodology using phase-transfer catalysis.
Generally, there are two synthetic strategies for the preparation of aminonaph-
thols. In the direct and convenient method, the aminonaphthol derivatives have been
synthesized by the reaction of aldehyde, 2-naphthol and aliphatic amines in organic
solvents such as EtOH, MeOH, and Et2O (Scheme 1, path I). Another approach is
the hydrolysis of preformed amidoalkylnaphthols (Scheme 1, path II). For this
reason, the syntheses of amidoalkyl naphthols have attracted growing interest. It is
noticeable that the direct path of this method is unsuccessful for the synthesis of
aminonaphthols.
Recently, the use of Lewis acids as a catalyst has gained special attention because
of their ready availability, inexpensiveness, and unique reactivity under mild
conditions. Several examples of Brønsted and Lewis acids, such as boric acid [16],
deep eutectic solvents [17], acidic ionic liquids [18, 19], InCl3 [20], Fe(HSO4)3 [21],
BiCl3 [22] and LiClO4 [23] have been used as a catalyst for the synthesis of amido-
and aminonaphthols.
The heterogenization of the existing homogeneous catalysts can potentially
provide novel recyclable and reusable solid catalysts that have uniform and
precisely engineered active sites similar to their homogeneous counterparts, and
therefore preserve the desirable attributes of both systems. This strategy not only
Scheme 1 Two convenient synthetic strategies for the preparation of aminonaphthols
123

An efficient and green method for the synthesis of Betti…
Scheme 2 One-pot synthesis of aminonaphthols, using nano-SiO2–H3BO3 as a catalyst, under solvent-
free conditions
reduces the loss of catalyst but also enhances reusability, making the catalyst cost–
effective and promising for wide industrial applications. There are some reports for
the use of heterogeneous catalytic systems such as non-ionic surfactant [24],
nanocrystalline MgO [25], supported copper triflate [26] and nano-Fe3O4 [27] based
on the first method and zeolite [28], HClO4–SiO2 [29], FeCl3/SiO2 [30], and MoO3/
SiO2 [31] based on second method for the synthesis of Betti bases.
Boric acid (H3BO3) is a very weak acid, with an ionization constant of about
pKa = 9.2 [32]. It is a very stable compound and relatively benign to humans [33].
Therefore, this reagent has been utilized in various reactions such as the aza-
Michael reaction [34], Biginelli reaction [35] and Mannich reaction [36].
Furthermore, it has also been used for the preparation of compounds such as 1,5-
benzodiazepine derivatives [37], nitro-aromatic compounds [38], dibenzoxanthenes
[39], a-aminophosphonates [40], a-hydroxyamides [41] and 1-amidoalkyl-2-naph-
thols [16]. As mentioned, boric acid successfully catalyzed the synthesis of
amidoalkylnaphthols as Betti base precursors (Scheme 1, path II) [16], but this
catalyst is inefficient for the direct synthesis of alkylaminonaphthols as Betti bases
[24, 27]. The use of a nano-structured support allowing the boric acid to be
dispersed over a large surface may result in an increase of its catalytic activity.
As a part of our ongoing interest in the efficient synthesis of Betti bases
[22, 42, 43], here, we have demonstrated a facile route for the synthesis of nano-
SiO2–H3BO3 as a novel recyclable heterogeneous catalyst which can be utilized as
an ideal promoter for the direct and efficient synthesis of aminonaphthol derivatives
via three-component condensation of b-naphthol, aldehydes and amines under mild,
one-pot and solvent-free conditions (Scheme 2). The novel synthesized catalyst was
characterized with the help of powder FE-SEM, EDX, FT-IR spectra and TGA
analyses.
Experimental
All chemicals were purchased from Merck or Aldrich and were used without further
purification. Melting points were determined on a MEL-TEMP model 1202D and
are uncorrected. FT-IR spectra were recorded on a Bruker Tensor 27 spectrometer
as KBr disks. The 1H NMR spectra were recorded with a Bruker Spectrospin
Avance 400 spectrometer. 13C NMR spectra were determined on the same
123

R. Teimuri-Mofrad et al.
instrument at 100 MHz. Field emission scanning electron microscopy (FE-SEM)
used a Tescan MIRA3 instrument). All chemical shifts were reported as d (ppm)
relative to solvent peaks as internal standards, and coupling constants (J) are given
in Hz.
Synthesis of nano-SiO2–H3BO3
¨
Silica nanoparticles were prepared via an improved Stober method [44]. In a typical
procedure, a solution containing 100 mL of methanol, 10 mL of 28 wt% ammonia,
1 mL of deionized water and 8.32 g of TEOS was completely mixed and was
continually stirred at 60 °C for 2 h. The condensation progress of TEOS was easily
observed by the color change in the solution, from colorless to opalescent, during
the formation of silica suspension. The silica suspension was centrifuged to obtain
the precipitate of silica nano-particles (SNPs). The precipitates of the SNPs were
collected and dried under vacuum at 70 °C for 4 h. The synthesized SNPs (1 g)
were dispersed in absolute ethanol (50 mL) and boric acid (0.5 g) was added to a
suspension. The mixture was stirred at 80 °C till the evaporation of the solvent. The
solid was repeatedly washed with ethanol to remove any unadsorbed boric acid,
filtered off and dried under vacuum at 80 °C for 6 h to furnish the catalyst as a white
powder. The synthesis procedure of the SNPs is shown in ‘‘Synthesis and
characterization of nano-SiO2–H3BO3’’
General procedure for the synthesis of aminonaphthols
To a mixture of 2-naphthol (1 mmol), aldehyde (1 mmol) and amine (1.2 mmol)
was added nano-SiO2–H3BO3 (15 mg). The mixture was stirred at 40 °C under
solvent-free conditions in an oil bath for certain periods as indicated in Table 2.
After completion of the reaction, indicated by TLC (acetone/chloroform/n-hexane:
1/2/5), the reaction mixture was dissolved in hot ethanol, the catalyst was recovered
by filtration and the product was recrystallized from ethanol to give the
corresponding aminonaphthols as a pure solid. The characterized data of the known
compounds were in good agreement with those in the literature. The recovered
catalyst was washed with EtOH, dried and reused for the next run. The catalyst was
recovered and reused for five times without any significant changes in the yield or
the reaction time. All new compounds were characterized by mp, IR, 1H NMR, 13
NMR and elemental analysis (C, H, and N).
C
Spectral data of new compounds
1-[(2-Bromo-5-fluorophenyl)(piperidin-1-yl)methyl]naphthalen-2-ol
(4g) Light
brown solid; mp: 159–161 °C; FT-IR (KBr) m 3445, 3062, 2932, 2853, 1592,
1
1461, 1205, 1070 cm-1; H NMR (400 MHz, CDCl3): d 1.22–1.34 (1H, m, CH2),
1.46–1.57 (1H, m, CH2), 1.68–1.77 (4H, m, CH2), 2.29–2.36 (1H, m, –NCH),
2.41–2.47 (1H, m, –NCH), 2.61–2.64 (1H, m, –NCH), 3.29–3.32 (1H, m, –NCH),
5.75 (1H, s, methine-H), 6.77–6.82 (1H, m, Ar–H), 7.15 (1H, d, J = 8.6 Hz, Ar–H),
7.21–7.25 (1H, m, Ar–H), 7.35–7.39 (2H, m, Ar–H), 7.51–7.55 (1H, m, Ar–H),
123

An efficient and green method for the synthesis of Betti…
7.68–7.71 (2H, m, Ar–H), 7.80 (1H, d, J = 8.6 Hz, Ar–H), 14.13 (1H, s, OH) ppm;
13C NMR (100 MHz, CDCl3): d 22.9, 24.9, 25.4, 48.4, 53.7, 68.0, 114.5, 115.9,
116.2, 116.9, 117.2, 119.2, 120.3, 121.6, 125.7, 125.9, 127.5, 127.7, 127.8, 128.8,
129.3, 132.8, 132.9, 139.7, 139.8, 155.5, 160.3, 162.8 ppm; Anal. Calcd. For
C22H21BrFNO: C, 63.78; H, 5.11; N, 3.38; Found: C, 63.55; H, 5.14; N, 3.35%.
1-[Morpholino(thiophen-2-yl)methyl]naphthalen-2-ol (4q) Light brown solid; mp:
1
197–199 °C; FT-IR (KBr) m 3336, 3061, 2925, 2856, 1599, 1476, 1229 cm-1; H
NMR (400 MHz, CDCl3): d 2.30–2.35 (2H, m, –NCH), 2.68 (1H, m, –NCH), 3.05
(1H, m, –NCH), 3.63–3.81 (4H, m, –OCH), 5.44 (1H, s, methine-H), 6.86–6.88 (1H,
m, Ar–H), 7.13–7.17 (2H, m, Ar–H), 7.20 (1H, d, J = 3.1 Hz, Ar–H), 7.26 (1H, t,
J = 7.4 Hz, Ar–H), 7.42 (1H, t, J = 7.4 Hz, Ar–H), 7.67–7.73 (2H, m, Ar–H), 7.89
(1H, d, J = 8.6 Hz, Ar–H), 12.64 (1H, s, OH) ppm; 13C NMR (100 MHz, CDCl3):
d 50.4, 52.2, 64.6, 65.8, 114.2, 118.6, 119.7, 121.7, 125.1, 125.5, 125.7, 126.4,
127.7, 127.9, 128.9, 130.9, 140.3, 153.2 ppm; Anal. Calcd. For C19H19NO2S: C,
70.13; H, 5.89; N, 4.30; S, 9.85; Found: C, 69.89; H, 5.92; N, 4.28; S, 9.73%.
1-[(5-Methylmfuran-2-yl) (Morpholino) methyl] naphthalen-2-ol (4r) White
solid; mp: 193–195 °C; FT-IR (KBr) m 3449, 3060, 2960, 2922, 1621, 1516,
1116 cm-1; 1H NMR (400 MHz, CDCl3): d 2.23 (1H, s, –CH3), 2.35–2.47 (4H, m,
–NCH), 3.67–3.75 (4H, m, –OCH), 5.23 (1H, s, methine-H), 5.82 (1H, d,
J = 2.2 Hz, Ar–H), 6.20 (1H, d, J = 3.0 Hz, Ar–H), 7.12 (1H, d, J = 8.8 Hz, Ar–
H), 7.24–7.27 (1H, m, Ar–H), 7.41 (1H, t, J = 7.6 Hz, Ar–H), 7.68 (1H, d,
J = 8.8 Hz, Ar–H), 7.72 (1H, d, J = 8.1 Hz, Ar–H), 7.80 (1H, d, J = 8.6 Hz, Ar–
H), 12.51 (1H, s, OH) ppm; 13C NMR (100 MHz, CDCl3): d 12.7, 50.8, 62.6, 65.8,
105.6, 109.6, 111.4, 118.6, 119.8, 121.5, 125.6, 127.6, 127.8, 128.8, 131.3, 148.5,
151.2, 154.4 ppm; Anal. Calcd. For C20H21NO3: C, 74.28; H, 6.55; N, 4.33; Found:
C, 74.03; H, 6.58; N, 4.30%.
Results and discussion
This research was performed in two stages. Initially, nano-silica was prepared by
mixing nano-silica and H3BO3 in ethanol, and boric acid-functionalized SNPs
(BSNPs/nano-SiO2–H3BO3) were synthesized. In the second stage, aminonaphthol
derivatives were successfully synthesized in the presence of nano-SiO2–H3BO3 at
room temperature.
Synthesis and characterization of nano-SiO2–H3BO3
Boric acid-functionalized silica nanoparticles (BSNPs) as a nanocatalyst were
synthesized in two steps (Fig. 1). First, SNP shells were made by a liquid chemical
¨
approach based on the well-known Stober process, which involves the hydrolysis
and condensation of a TEOS in methanol in the presence of water with ammonia as
the catalyst [43]. Subsequently, synthesized SNPs reacted with boric acid in ethanol
to obtain the desired BSNPs.
123

R. Teimuri-Mofrad et al.
Fig. 1 Schematic diagram for synthesis of boric acid-functionalized silica nanoparticles (BSNPs)
FT-IR spectra were performed to study the structures and identify the functional
group of the BSNPs (Fig. 2). The intense and broad band appearing at 1102 cm-1 is
related to Si–O–Si asymmetric stretching and the band at 800 cm-1 is related to Si–O–
Si symmetric stretching. The band at 470 cm-1 is assigned to the bending vibration of
Si–O–Si. The broad band at 3421 cm-1 is due to the stretching vibration of O–H. The
characteristic bands located at 947 and 566 cm-1 were assigned to the stretching and
bending vibrations of the B–O–Si groups and a band located at 1398 cm-1 is due to the
B–O stretching vibrations [44, 45]. These results indicate the loading of H3BO3 on the
nano-SiO2 surface and the formation of the BSNPs.
The TGA profiles of the BSNPs exhibit two steps of weight loss (Fig. 3). The
first weight loss occurs below 120 °C and is attributed to the evaporation of
physically adsorbed water. The further weight loss occurs between 120 and 500 °C
and is related to the dehydroxylation of the remaining silanol groups in the BSNPs.
The surface morphology and spherical structure of the catalyst was investigated
by FE-SEM. The images show that the particle size (mean particle diameter of about
100 nm) and sphere shape of nano-SiO2 were retained after adsorption of H3BO3
(Fig. 4). The presence of elements Si, O and B in nano-SiO2–H3BO3 was confirmed
by EDX analysis (Fig. 5).
Catalytic investigations
In the search of best catalytic system for the synthesis of aminonaphthols, the
reaction of 2-naphthol (1a) with benzaldehyde (2a) and piperidine (3a) was chosen
123

An efficient and green method for the synthesis of Betti…
Fig. 2 FTIR spectra of the boric acid-functionalized silica nanoparticles
101
100
99
98
97
96
95
94
93
92
0
100
200
300
400
500
600
Temperature (oC)
Fig. 3 TGA of the boric acid-functionalized silica nanoparticles
as a model reaction to investigate the feasibility of the strategy and to optimize the
reaction conditions. For this purpose, the efficiency of SiO2–H3BO3 in different
conditions was compared with a variety of reported catalysts/processes. The results
are summarized in Table 1.
The results show that only a trace amount of aminonaphthols were obtained in
the absence of a catalyst even after 12 h (Table 1, entries 1–3). It was found that the
use of a catalyst was essential for the synthesis of aminonaphthols. Even with a
temperature increase to 100 °C for this reaction, there was no appreciable
improvement in yield (Table 1, entry 4). To obtain an efficient, eco-friendly and
reusable catalytic system for the synthesis of aminonaphthols, different Bronsted
acid and supported metal Lewis acid catalysts such as TsOH, TiO2, SiO2, TiO2–
SiO2, BF3–SiO2, ZnCl2–SiO2, Zn(OTf)2–SiO2 were investigated (Table 1, entries
5–16).
123

R. Teimuri-Mofrad et al.
Fig. 4 FE-SEM image of the boric acid-functionalized silica nanoparticles
Fig. 5 EDX analysis of the boric acid-functionalized silica nanoparticles
To study the role of SiO2, the reaction was tested in the presence of SiO2 (10 mg)
and the observed relativity increased as compared to the catalyst-free reaction
(Table 1, entries 4, 6). In the same way, the presence of metal Lewis acid as a
catalyst increased the yield of the reaction (Table 1, entry 8). It is also observed that
with catalyst support on SiO2, as compared to only SiO2 and metal Lewis acid, the
yield increased (Table 1, entries 8, 9, 14, 15). Among all screened catalysts, nano-
SiO2–H3BO3 gave the best result in terms of yield and reaction time (Table 1, entry
123

An efficient and green method for the synthesis of Betti…
Table 1 Reported catalysts/processes for the synthesis of aminonaphthols and optimization catalytic
activity of SiO2–H3BO3 in this reaction
Entry Catalyst (mol%–mg)
Solvent Temp (°C) Time (h) Yield (%)b Lit references
1
Nonea
Nonea
Nonea
Nonea
Neat
rt
rt
12
12
12
12
4
Trace
Trace
Trace
30B
35
This work
This work
[26]
2
EtOH
3
Toluene rt
4
Toluene 100
[26]
5
TsOH (5 mol%)c
SiO2 (10 mol%)a
SiO2 (10 mol%)a
TiO2 (5 mol%)a
TiO2–SiO2 (10 mol%)a
BF3–SiO2 (10 mol%)a
ZnCl2–SiO2 (10 mol%)a
Zn(OTf)2–SiO2 (10 mol%)a
H3BO3 (5 mol%)c
H3BO3 (5 mol%)a
SiO2–H3BO3 (5 mg)a
water
rt
[24]
6
Toluene 100
12
12
4
62
[26]
7
Water
Neat
rt
rt
30B
25
This work
[27]
8
9
Toluene rt
Toluene rt
Toluene rt
Toluene rt
12
12
12
12
4.5
12
12
12
8
54
[26]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
a
37
[26]
56
[26]
74
[26]
Water
Water
Water
rt
rt
rt
rt
rt
rt
rt
15
[24]
20B
57
This work
This work
Our catalyst
Our catalyst
Our catalyst
Our catalyst
Our catalyst
Our catalyst
Our catalyst
Our catalyst
Nano-SiO2–H3BO3 (10 mg)a Water
Nano-SiO2–H3BO3 (15 mg)a Water
Nano-SiO2–H3BO3 (20 mg)a Water
Nano-SiO2–H3BO3 (15 mg)a EtOH
76
82
12
12
12
1
80
72
Nano-SiO2–H3BO3 (15 mg)a Toluene rt
78
Nano-SiO2–H3BO3 (15 mg)a Neat
Nano-SiO2–H3BO3 (15 mg)a Neat
Nano-SiO2–H3BO3 (15 mg)a Neat
rt
89
40
60
40 min
1
94
94
Reaction conditions: 2-naphthol/Benzaldehyde/piperidine/= 1:1:1.2
b
c
Isolated yield
Reaction conditions: 2-naphthol/Benzaldehyde/pyrrolidine/= 1:1:1.2
16). In contrast, TiO2–SiO2, BF3–SiO2, ZnCl2–SiO2 and Zn(OTf)2–SiO2 did not
afford the desired product in good yields. In order to optimize the reaction
conditions, the model reaction was catalyzed with different quantities (5, 7.5 and
10 mol%) of nano-SiO2–H3BO3 as the catalyst, with different solvents and
temperatures. As Table 1 shows, the best result (entry 22, 94% yield) was obtained
123

R. Teimuri-Mofrad et al.
Table 2 The synthesis of aminonaphthols with nano SiO2–H3BO3
Time
(min)
Yield
(%)b
Obs.mp
(oC)
Lit.mp
(oC)
Entry
R
Aldehyde
Amine
Product
193–
1
H
40
94
192–194
195[26]
150–
2
3
4
H
H
H
35
92
151–153
152[42]
177–
30
95
178–179
179[42]
169–
40
92
169–170
171[42]
240°C
(dec.)
240°C
5
H
45
88
(dec.) [42]
170–
6
H
40
92
171–173
172[22]
123

An efficient and green method for the synthesis of Betti…
Table 2 continued
Time
(min)
Yield
(%)b
Obs.mp
(oC)
Lit.mp
(oC)
Entry
R
Aldehyde
Amine
Product
7
H
35
94
159–161
–
182–
8
Br
35
92
181–183
184[22]
174–
9
H
40
94
174–175
176[42]
163–
10
H
35
92
163–164
165[42]
160–
11
12
13
H
H
H
35
35
45
93
94
88
161–163
156–157
134–136
162[42]
155–
157[42]
135–
137[42]
123

R. Teimuri-Mofrad et al.
Table 2 continued
Time
(min)
Yield
(%)b
Obs.mp
(oC)
Lit.mp
(oC)
Entry
R
Aldehyde
Amine
Product
164–
14
H
40
92
163–165
166[22]
179–
15
Br
40
92
180–182
181[22]
163–
16
Br
35
94
164–165
165[22]
17
H
40
91
197–199
–
18
H
40
92
193–195
–
177–
19
Br
35
93
177–179
179[22]
123

An efficient and green method for the synthesis of Betti…
Table 2 continued
Time
(min)
Yield
(%)b
Obs.mp
(oC)
Lit.mp
(oC)
Entry
R
Aldehyde
Amine
Product
134–
20
H
45
88
90
90
133–135
136[26]
107–
22
H
CH2O
35
108–110
109[46]
Gummy
solid
Gummy
23
H
CH2O
40
solid [46]
Reaction conditions: 2-naphthol/aldehyde/amine = 1:1:1.2 and nano SiO2–H3BO3 (7.5 mg) at 40 °C
under solvent free condition
a
Isolated yield
when the reaction was performed using 7.5 mol% of H3BO3–nano-SiO2 under
solvent-free conditions at 40 °C.
After optimization of the reaction conditions, to explore the scope and generality
of this procedure, condensation reactions of 2-naphthols with a variety of aromatic
aldehydes and aliphatic amines were examined in the presence of nano-SiO2–
H3BO3 (15 mg) at 40 °C under solvent-free conditions (Table 2).
A plausible mechanistic rationalization of the nano-SiO2–H3BO3, catalyzed
reaction is shown in Scheme 3. We assume that the Lewis acid–base interaction
between the catalyst and the oxygen of the aldehyde carbonyl group leads to an
electrophilic carbon atom. Condensation of the amine with activated aldehyde
followed by dehydration generates an imine intermediate. Consequently, the
nucleophilic attack of the 2-naphthol to imine gives the desired product as depicted
in Scheme 3.
123

R. Teimuri-Mofrad et al.
−
δ
δ+
Scheme 3 Proposed mechanism for the BSNPs catalyzed synthesis of aminonaphthols via a one-pot,
three-component reaction
Recyclability of the catalyst
We also investigated the recycling of the catalyst under solvent-free conditions
using a model reaction in the presence of nano-SiO2–H3BO3 (15 mg) at 40 °C.
After completion of the reaction, the reaction mixture was dissolved in hot ethanol
and the catalyst was recovered by filtration and the crude solid product was obtained
by recrystallization from ethanol. The catalyst was washed twice with hot ethanol
and dried in vacuum. The recovered catalyst was reused for 4 runs without any loss
of its weight or activities (Fig. 6).
To highlight the quality, applicability and efficiency of the present work in
comparison to other reported results in the literature, we compared the results of the
nano-SiO2–H3BO3 catalyzed reactions with those of the recently reported method-
ologies for the synthesis of aminonaphthol derivatives. As shown in Table 3, the
123

An efficient and green method for the synthesis of Betti…
Catalyst Recyclability
Product Yield (%)
Catalyst Yield (%)
Time (min)
120
100
80
60
40
20
0
98
95
94
94
93
92
91
90
89
88
50
45
45
40
40
1
2
3
4
5
Run of use
Fig. 6 Recovery and reusability of the BSNPs for the synthesis of 4a
Table 3 Comparison of the present method with the recently reported green methods
Aminonaphthols
Catalyst/solvent/condition
Time
Yield (%) References
18-crown-6/PhCH3/refluxa
LiClO4/Et2O/rt
12 h
87
[15]
[23]
[24]
[25]
[26]
[27]
[42]
60 min 70
Non-ionic surfactant/water/rt
Nanocrystalline MgO/water/rt
Cu(OTf)2–SiO2 water/40 °C
Nanoparticle Fe3O4/solvent free/rt
DMEA/solvent free/50 °C
2.5 h
2 h
90
90
45 min 92
1.5 h 92
40 min 87
94
b
_
nano-SiO2–H3BO3/solvent free/40 °C 40
a
One of the most valuable methodologies reported by Katritzky et al. and the benzotriazole moiety from
N-[a-(dialkylamino)alkyl]benzotriazoles were used instead of preformed iminium salts and the reaction
was carried out in two steps under refluxing toluene
b
Our work
nano-SiO2–H3BO3 acts as an effective catalyst with respect to the solvent-free
conditions, short reaction times and high yields of the obtained products.
Conclusions
In conclusion, we have designed and synthesized H3BO3– nano-SiO2 for the first
time and used it as a highly efficient heterogeneous catalyst for the direct synthesis
of aminonaphthols. A series of aminonaphthols were synthesized via a one-pot
three-component reaction of aldehydes, amines and 2-naphthol in the presence of
the catalyst under solvent-free conditions. The operational simplicity of the
123

R. Teimuri-Mofrad et al.
procedure, short reaction times, easy work-up, extremely mild reaction conditions
and environmental friendliness make this method more attractive. Furthermore, a
wide range of synthesized aminonaphthols show the universality of this method. In
addition, the catalyst can be recovered and easily recycled for at least five times
without loss of efficacy.
Supporting information
Supplementary data (full experimental procedures and characterization data)
associated with this article can be found via the ‘‘Supplementary Content’’ section
of this article’s webpage.
Acknowledgements The authors would like to acknowledge the financial support from the Iran National
Science Foundation (INSF) and the University of Tabriz.
References
1. C. Cardellicchio, M.A.M. Capozzi, F. Naso, Tetrahedron 21, 507–517 (2010)
´
¨
2. I. Szatmari, F. Fu¨lop, Tetrahedron 69, 1255–1278 (2013)
3. M. Gerlach, C. Maul, US Patent 7,202,242 B2 (2007)
4. N. Gyemant, H. Engi, Z. Schelz, I. Szatmari, D. Toth, F. Fulop, J. Molnar, P. de Witte, Br. J. Cancer
103, 178–185 (2010)
5. A.Y. Shen, C.T. Tsai, C.L. Chen, Eur. J. Med. Chem. 34, 877–882 (1999)
6. I. Szatmari, A. Heteny, L. Lazar, F. Fulop, J. Heterocycl. Chem. 41, 367–373 (2004)
7. V.D. Dhakane, S.S. Gholap, U.P. Deshmukh, H.V. Chavan, B.P. Bandgar, C. R. Chim. 17, 431–436
(2014)
8. M. Heydenreich, A. Koch, S. Klod, I. Szatmari, F. Fulop, E. Kleinpeter, Tetrahedron 62,
11081–11089 (2006)
9. M. Ghandi, A. Olyaei, S. Raoufmoghaddam, J. Heterocycl. Chem. 46, 914–919 (2009)
10. I. Szatmari, T.A. Martinek, L. Lazar, A. Koch, E. Kleinpeter, K. Neuvonen, F. Fulop, J. Org. Chem.
69, 3645–3653 (2004)
11. H.V. Poel, G. Guilaumet, V.M. Massuard, Tetrahedron Lett. 43, 1205–1208 (2002)
12. P. Zang, E.A. Terefenko, A. Fensome, J. Wrobel, R. Winneker, Z. Zang, Bioorg. Med. Chem. Lett.
13, 1313–1316 (2003)
13. X. Xu, C. Wang, J. He, Y. Hu, H. Hu, Tetrahedron Lett. 43, 8367–8369 (2002)
14. M. Marinova, K. Kostova, P. Tzvetkova, M. Tavlinova-Kirilova, R. Nikolova, B. Shivachev,
Tetrahedron Asymmetry 24, 1453–1466 (2013)
15. A.R. Katritzky, A.A.A. Abdel-Fattah, D.O. Tymoshenko, S.A. Belyakov, I. Ghiviriga, P.J. Steel, J.
Org. Chem. 64, 6071–6075 (1999)
16. A. Shahrisa, S. Esmati, M. Gholomhosseini, Nazari. J. Chem. Sci. 124, 927–931 (2012)
17. N. Azizi, M. Edrisi, Res. Chem. Intermed. (2016). doi:10.1007/s11164-016-2628-2
18. H.R. Shaterian, A. Hosseinian, Res. Chem. Intermed. 40, 3011–3019 (2014)
19. H.R. Shaterian, A. Hosseinian, Res. Chem. Intermed. 41, 793–801 (2015)
20. N.L. Chavan, P.N. Naik, S.K. Nayak, R.S. Kusurkar, Synth. Commun. 40, 2941–2947 (2010)
21. H.R. Shaterian, H. Yarahmadi, M. Ghashang, Bioorg. Med. Chem. Lett. 18, 788–792 (2008)
22. A. Shahrisa, R. Teimuri-Mofrad, M. Gholamhosseini-Nazari, Synlett 26, 1031–1038 (2015)
23. M.R. Saidi, N. Azizi, M.R. Naimi-Jamal, Tetrahedron Lett. 42, 8111–8113 (2001)
24. A. Kumar, M.K. Gupta, M. Kumar, Tetrahedron Lett. 51, 1582–1584 (2010)
25. B. Karmakar, J. Banerji, Tetrahedron Lett. 52, 4957–4960 (2011)
26. S.D. Dindulkar, V.G. Puranik, Y.T. Jeong, Tetrahedron Lett. 53, 4376–4438 (2012)
27. F. Janati, M.M. Heravi, A.M. Shokraie, Synth. React. Inorg. Met. Org. Chem. 45, 1–5 (2015)
123

An efficient and green method for the synthesis of Betti…
28. S.R. Mistry, R.S. Joshi, K.C. Maheria, J. Chem. Sci. 123, 427–432 (2011)
29. H.R. Shaterian, H. Yarahmadi, M. Ghashang, Tetrahedron 64, 1263–1269 (2008)
30. J.S. Ghomi, S. Zahedi, Monatsh. Chem. 144, 687–693 (2013)
31. F. Moeinpour, N. Dorostkar-Ahmadi, A. Sardashti-Birjandi, A. Khojastehnezhad, M. Vafaei, Res.
Chem. Intermed. 40, 3145–3152 (2014)
32. M.C.C. Azevedo, A.M.V. Cavaleiro, J. Chem. Edu. 89, 767–770 (2012)
33. D.G. Hall, Boronic Acids: Preparation and Applications in Organic Synthesis, Medicine and
Materials, 2nd edn. (Wiley-VCH, Weinheim, 2011)
34. M.K. Chaudhuri, S. Hussain, M.L. Kantam, B. Neelima, Tetrahedron Lett. 46, 8329–8331 (2005)
35. S. Tu, F. Fang, C. Miao, H. Jiang, Y. Feng, Y. Shi, X. Wang, Tetrahedron Lett. 44, 6153–6155 (2003)
36. C. Mukhopadhyay, A. Datta, R.J. Butcher, Tetrahedron Lett. 50, 4246–4250 (2009)
37. X. Zhou, M.Y. Zhang, S.T. Gao, J.J. Ma, C. Wang, C. Liu, Chin. Chem. Lett. 20, 905–908 (2009)
38. H. Valizadeh, H. Gholipour, C. R. Chim. 14, 963–966 (2011)
39. Z. Karimi-Jaberi, M. Keshavarzi, Chin. Chem. Lett. 21, 547–549 (2010)
40. Z. Karimi-Jaberi, M. Amiri, Heteroat. Chem. 21, 96–98 (2010)
41. J.S. Kumar, S.C. Jonnalagadda, V.R. Mereddy, Tetrahedron Lett. 51, 779–782 (2010)
42. A. Shahrisa, R. Teimuri-Mofrad, M. Gholamhosseini-Nazari, Mol. Divers. 19, 87–101 (2014)
43. R. Teimuri-Mofrad, A. Shahrisa, M. Gholamhosseini-Nazari, N. Arsalani, Res. Chem. Intermed. 42,
3425–3439 (2016)
44. H.T. Lu, Colloid J. 75, 311–318 (2013)
45. J. Clark, Chem. Commun. 19, 2135–2136 (1998)
46. S.S. Ganesan, N. Rajendran, S.I. Sundarakumar, A. Ganesan, B. Pemiah, Synthesis 45, 1564–1568
(2013)
123