2-Hydroxy-5-sulfobenzoic acid: An efficient organocatalyst for the three-component synthesis of 1-amidoalkyl-2-naphthols and 3,4-disubstituted isoxazol-5(4H)-ones

Article abstract of DOI:10.1007/s11164-014-1844-x

2-Hydroxy-5-sulfobenzoic acid (2-HSBA) efficiently catalyzed the one-pot three-component synthesis of a wide variety of 1-amidoalkyl-2-naphthols and 3,4-disubstituted isoxazol-5(4H)-ones. The three-component process of substituted benzaldehydes, 2-naphthol, and amides (benzamide and acetamide) or urea occur using 10 mol% of 2-HSBA as an organocatalyst under solvent-free reaction conditions (SFRCs) at 100 °C. It was also found that the best results for the preparation of 3,4-disubstituted isoxazol-5(4H)-ones were achieved using 15 mol% of 2-HSBA under aqueous conditions at room temperature. The reactions are easy to do and were completed within 3-25 min (for amidoalkyl naphthols), and 70-120 min (for 3,4-disubstituted isoxazol-5(4H)-ones), while the expected products were obtained in 82-97 % yields. The catalyst can be recovered and reused several times in the template reactions. This procedure offers the advantages of convenience, simple operational procedure, cost-effectiveness, no use of hazardous organic solvents, and the commercial availability of the catalyst.

Full text of DOI:10.1007/s11164-014-1844-x

Res Chem Intermed
DOI 10.1007/s11164-014-1844-x
2-Hydroxy-5-sulfobenzoic acid: an efficient
organocatalyst for the three-component synthesis
of 1-amidoalkyl-2-naphthols and 3,4-disubstituted
isoxazol-5(4H)-ones
•
Hamzeh Kiyani Hassan Darbandi
•
•
Asiyeh Mosallanezhad Fatemeh Ghorbani
Received: 5 August 2014 / Accepted: 5 October 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract 2-Hydroxy-5-sulfobenzoic acid (2-HSBA) efficiently catalyzed the one-
pot three-component synthesis of a wide variety of 1-amidoalkyl-2-naphthols and
3,4-disubstituted isoxazol-5(4H)-ones. The three-component process of substituted
benzaldehydes, 2-naphthol, and amides (benzamide and acetamide) or urea occur
using 10 mol% of 2-HSBA as an organocatalyst under solvent-free reaction con-
ditions (SFRCs) at 100 °C. It was also found that the best results for the preparation
of 3,4-disubstituted isoxazol-5(4H)-ones were achieved using 15 mol% of 2-HSBA
under aqueous conditions at room temperature. The reactions are easy to do and
were completed within 3–25 min (for amidoalkyl naphthols), and 70–120 min (for
3,4-disubstituted isoxazol-5(4H)-ones), while the expected products were obtained
in 82–97 % yields. The catalyst can be recovered and reused several times in the
template reactions. This procedure offers the advantages of convenience, simple
operational procedure, cost-effectiveness, no use of hazardous organic solvents, and
the commercial availability of the catalyst.
Keywords 2-Hydroxy-5-sulfobenzoic acid Á 1-Amidoalkyl-2-naphthols Á Three-
component reaction Á Water Á 3,4-disubstituted isoxazol-5(4H)-ones Á Solvent-free
Introduction
The one-pot multicomponent reaction (MCR) states that a process implemented
from three or more various substrates in a single vessel reaction. This attractive
approach is very successful in the preparation of various chemical libraries of eye-
catching organic compounds [1]. A one-pot three-component reaction (3CR) in the
organic synthetic chemistry that generates 1-aminoalkyl-2-naphthols via a MCR is
H. Kiyani (&) Á H. Darbandi Á A. Mosallanezhad Á F. Ghorbani
School of Chemistry, Damghan University, 36715-364 Damghan, Iran
e-mail: hkiyani@du.ac.ir
123

H. Kiyani et al.
called the Betti 3-component reaction (Betti-3CR). Betti-3CR, a very well-known
process, was introduced by Italian chemist Mario Betti in 1900 [2]. The Betti-3CR
represents an expedient protocol to achieve amidoalkyl naphthols, which are also
considered as the Betti base analogous (Fig. 1). Betti bases and related molecules
have attracted a lot of attention due to their applications in asymmetric synthesis [1],
catalytic organic transformations (for example, Mizoroki–Heck and Ullmann
coupling reactions) [3], and chiral shift reagents for carboxylic acids or chiral
auxiliaries for the synthesis of a-aminophosphonic acids [4].
1-Amidoalkyl-2-naphthols are very important precursors for the preparation of
significant bioactive 1-aminomalkyl-2-naphthols via amide hydrolysis, which
exhibit depressor, hypotensive and bradycardia effects in humans [5]. Amidoalkyl
naphthols can be used in pharmaceutical chemistry as anti-inflammatory, anthel-
mintic, antibacterial, and antiviral agents [6, 7]. On the other hand, 1-amidoalkyl-2-
naphthols and their N-substituted derivatives can be also transformed to 1,3-
oxazine-containing compounds as an special class of bioactive heterocycles that
present in many biologically important natural products and drug candidates [8–10],
which possess many biological activities such as antibiotic [11], antihypertensive
[12], analgesic [13], antimalarial [14], antitumor [15], antrheumatic [16], antian-
ginal [17], and anticonvulsant [18]. Consequently, the synthesis of derivatives of the
amidoalkyl naphthols is of much current importance for the research groups
working in the organic synthesis and medicinal chemistry fields. Numerous
approaches have been reported for the synthesis of these compounds. In these
¨
methods Lewis or Bronsted acids [19], nanomaterials [20–25], and carbohydrates
[26] have been applied to catalyze this transformation.
Metal-free organocatalytic multicomponent reactions (OMCRs) are one of the
effective green catalytic synthetic protocols for the synthesis of 1-amidoalkyl-2-
naphthols. Recently, newer metal-free organocatalytic versions, including sulfanilic
acid [27], pyridinium-based ionic liquid [28], cellulose-SO3H [29], 1-methyl-3-(2-
(sulfooxy)ethyl)-1H-imidazol-3-ium chloride [30], poly(4-vinylpyridinium butane
sulfonic acid) hydrogen sulfate [31], sulfamic acid [32], polyethylene glycol (PEG)-
based dicationic acidic ionic liquid (PEG1000-DAIL) [33], polymer-supported sulfonic
acid NKC-9 [34], 1,3-disulfonic acid imidazolium hydrogen sulfate{[Dsim]HSO4}
[35], N-(4-sulfonic acid)butyl triethylammonium hydrogen sulfate ([TEBSA][HSO4])
[36], heteropolyanion-based SO3H [37, 38], saccharin sulfonic acid [39], dodecyl-
phosphonic acid [40], 2-methylpyridinium trifluoromethanesulfonate ([2-MPyH]OTf)
[41], 2,4,6-trichloro-1,3,5-triazine (TCT) [42], melamine-Br3 [43], succinic acid [44],
N-bromophthalimide (NBPI) [45], and 1,3-dibromo-5,5-dimethylhydantoin (DBH)
[46] have been reported toward the synthesis of amidoalkyl naphthols. Despite these
procedures, newer methodologies for the synthesis of amidoalkyl naphthol derivatives
are still in demand.
The isoxazol nucleus, on the other hand, is a key five-membered cyclic oxime
ester, bearing one oxygen and one nitrogen atoms at adjacent positions, making an
attractive target in bioorganic, synthetic organic chemistry, and the pharmaceutical
industry, as well as also being building blocks in organic synthetic chemistry [47–
49]. Isoxazol-containing heterocycles exhibit a number of applications in the wide
variety of fields including merocyanine dyes [50, 51] and liquid crystalline materials
123

2-Hydroxy-5-sulfobenzoic acid
O
Fig. 1 General structure of
Betti bases (A), and amidoalkyl
naphthols (B)
Ar(R)
NH
OH
R1
N
Ar
Ar
R2
OH
A
B
[52]. In addition, many compounds containing the isoxazol ring moiety are
commonly found to be associated with diverse biological activities [53–59], such as
antimicrobial, fungicidal, anticonvulsant, HDAC inhibitory, protein-tyrosine phos-
phatase 1B (PTP1B) inhibitory, analgesic, antioxidant, anti-apoptotic, anti-obesity,
COX-2 inhibitory, nematicidal, anti-nociceptive, anti-inflammatory, antiviral, anti-
tubercular, herbicidal, inhibitor of protein kinase C (PKC), and antineoplastic, as
well as being known to possess anti-mycobacterial effects. Furthermore, the
isoxazol core is also a structural component of many drugs, for example, as inhibitor
of tumor necrosis factor-alpha (TNF-a) [60], sulfisoxazoles [61], and antibiotics
[62, 63], and has been used as an anti-androgen agent [64, 65]. Isoxazol-5(4H)-ones
are powerful proarmoatic acceptors and can also be used for the development of
optical storage, nonlinear optical research [50, 51], light-conversion molecular
devices [66], and filter dyes in photographic films [67]. A number of interesting
compounds with isoxazol nucleus are shown in Fig. 2.
During recent years, 3,4-disubstituted isoxazol-5(4H)-ones have been prepared
by using catalytic amounts of sodium benzoate [68], sodium sulfide [69], sodium
silicate [70], DABCO [71], nano-Fe2O3, clinoptilolite and H3PW12O40 [72]. The
3CR of b-oxoesters, hydroxylamine hydrochloride, and aryl aldehydes using
different conditions and techniques, such as sodium acetate and visible light [73],
pyridine under ultrasonic irradiation [74, 75], pyridine under reflux [76, 77], and
catalyst-free/grinding or heating [78], also provides isoxazol-5(4H)-ones. Also, we
synthesized the same arylmethylene isoxazol-5(4H)-ones by using catalysts
including sodium ascorbate [78], sodium citrate [80], sodium saccharin [81],
sodium tetraborate [82], sodium azide [83], boric acid [84], and potassium
phthalimide (PPI) [85].
It is well understood that organocatalysts are simple organic molecules able to
promote a wide range of chemical transformations via various activation modes and
the mildness of the reaction conditions required. They also typically have prominent
characteristics including metal-free environment, relatively low toxicity, simple
functionality, air stability, low-cost, and biological friendliness [86–89]. Moreover,
the elimination of solvents, particularly toxic solvents in chemical processes, is one
of the most important aspects of green chemistry, and there has been much attention
in the implementation of organic reactions under SFRCs. The solvent-free
procedures often exhibit significant rate enhancements due to increased reactant
concentrations. High efficiency, mild conditions, clean, cost-effectiveness, handling,
and economical friendliness are the other striking features of the reactions in
123

H. Kiyani et al.
-
r
r
Oi P
N
NH
N
O
O
N
O
R
l
C
N
N
N
O
O
O
O
O
N
H
An anti-androgen,
N
O
A fungicide
F
=
O
R
H Ph H
OC
,
7g
in this report
2
-
Oi P
O
Merocyanine dyes
A filter dye
N
R1
O
O
S
O
O
N
NHR
HN
NH2
N
O
R2
N
N
O
H
C
O
3
O
ulfisoxazole
s
Oxacillin and its derivatives
A TNF-alpha inhibitior
Fig. 2 Interesting isoxazol-containing compounds
solvent-less conditions [90, 91]. Growing interest in the conducting organic
transformations in SF presents an interesting field for this avenue of chemistry.
Water has a special place as the most attractive solvent in the synthetic
chemistry. Also, the use of water as the solvent not only decreases the risk of the
organic solvents but also increases the rate of chemical reactions. Also, MCR in
water can be visualized as a well-designed synthetic method to attain a wide range
of diverse molecular frameworks [92–95].
2-Hydroxy-5-sulfobenzoic acid (2-HSBA, 5-sulfosalicylic acid, SSA) was
employed as the fixation agent in the blood proteins [96], measuring urine protein
[97], evaluating the photo-reactivity of photo-catalysts [98], controlling the
morphology of nanocrystals [99], an extraction agent for vitamin B6 in food
[100], ligands for the formation of 3D coordination polymers with metal ions [101],
the dopant in polymerization [102], as an analytical reagent for iron [103] and
beryllium [104], and is effective in inducing tolerance to heat, drought and chilling
stress in plants [105]. This acid is also used as a catalyst in the preparation of
dihydropyrimidine-2(1H)-ones under microwave irradiation [106] and bis(indo-
lyl)methanes in methanol [107]. In this study, a simple one-vessel 3CR conden-
sation has been applied to the synthesis of a number of 1-amidoalkyl-2-naphthols
(4a–4ad) and 3,4-disubstituted isoxazol-5(4H)-ones (7a–s) in the presence of
2-HSBA as the catalyst under solvent-free and aqueous conditions, respectively
(Schemes 1, 2).
Experimental
General
All chemicals were purchased from Alfa Aesar and Aldrich and were used without
further purification, with the exception of 4-methylbenzaldehyde, 4-methoxylbenz-
aldehyde, benzaldehyde, thiophene-2-carbaldehyde, and thiophene-3-carbaldehyde
which were distilled before use. All solvents were distilled before use. The products
123

2-Hydroxy-5-sulfobenzoic acid
R
Z
O
R
NH
H
O
2-HSBA
(10 mol%)
2a-o
H
O
OH
Solvent-free, 100 °C
Z
+
H2N
O
HO2C
4a-ad
1
3a
: Z = CH3
: Z = Ph
3b
SO3H
H
O
3c
: Z = NH2
2-HSBA
Scheme 1 One-pot 3C synthesis of 1-amidoalkyl-2-naphtols (4a–ad) catalyzed by 2-HSBA
H
Ar
O
O
2
O
O
Ar
X
X
2-HSBA
(15 mol%)
NH
+
2
O
H
N
Water, RT
.
O
H
O
C
l
5
6a:
X = H
7a-s
6b
: X = Cl
Scheme 2 One-pot 3C synthesis of 3,4-disubstituted isoxazol-5(4H)-ones (7a–s) catalyzed by 2-HSBA
were characterized by comparison of their physical data with those of known
samples or by their spectral data. Melting points were measured on a Buchi 510
melting point apparatus and are uncorrected. NMR spectra were recorded at ambient
temperature on a BRUKER AVANCE DRX-400 MHz using CDCl3 or DMSO-d6 as
the solvent. FT-IR spectra were recorded on a Perkin-Elmer RXI spectrometer. The
development of reactions was monitored by thin layer chromatography (TLC)
analysis on Merck pre-coated silica gel 60 F254 aluminum sheets, visualized by UV
light.
Typical procedure for the preparation of 1-amidoalkyl-2-naphthols (4a-ad)
A mixture of 2-naphthol 1 (1 mmol), substituted aldehyde 2 (1 mmol), amide 3
(benzamide or acetamide, 1 mmol) or urea and 2-HSBA (10 mol%) was stirred at
100 °C in an oil bath for 3–30 min. After completion of the reaction (using TLC
analysis), the reaction mixture was allowed to cool to room temperature. Next, hot
ethyl acetate was added to the resulting mixture and then cooled to RT. The
resulting solid product was filtered off, washed with distilled water, and dried to
afford the targeted compounds. If further purification was needed, 1-amidoalkyl-2-
naphthols can be recrystallized from hot ethanol. The HSBA is soluble in water and
ethanol. The catalyst was recovered by evaporation of solvent from the filtrate,
123

H. Kiyani et al.
washed with the small amount of ethyl acetate, dried, and then used for the
subsequent reaction. Spectral data for 4c and 4p were as follows:
N-((2-hydroxynaphthalen-1-yl)(3-nitrophenyl)methyl)acetamide (4c)
1H NMR (400 MHz, DMSO-d6): d = 10.14 (s, 1H), 8.62 (d, J = 8.0 Hz, 1H),
8.02–7.99 (m, 2H), 7.84 (br, 1H), 7.78 (t, J = 8.6 Hz, 2H), 7.59–7.51 (m, 2H), 7.40
(t, J = 7.6 Hz, 1H), 7.26 (t, J = 7.4 Hz, 1H), 7.18 (d, J = 8.7 Hz, 1H), 7.16 (t,
J = 8.0 Hz, 1H), 2.02 (s, 3H); 13C NMR (100 MHz, DMSO-d6): d = 170.3, 153.9,
148.2, 145.9, 133.4, 132.7, 130.5, 130.1, 129.2, 128.9, 127.3, 123.2, 123.1, 121.8,
120.9, 118.9, 118.3, 48.2, 23.1.
N-((2-hydroxynaphthalen-1-yl)(3-nitrophenyl)methyl)benzamide (4p)
1H NMR (400 MHz, DMSO-d6): d = 10.42 (s, 1H), 9.15 (d, J = 8.0 Hz, 1H),
8.11–8.09 (m, 3H), 7.91–7.84 (m, 4H), 7.72 (d, J = 7.5 Hz, 1H), 7.60–7.49 (m,
5H), 7.41 (d, J = 8.0 Hz, 1H), 7.34 (t, J = 7.5 Hz, 1H), 7.25 (d, J = 8.5 Hz, 1H);
13C NMR (400 MHz, DMSO-d6): d = 166.8, 153.9, 148.2, 145.1, 134.4, 133.7,
132.8, 132.1, 130.5, 130.3, 129.3, 128.9, 128.8, 127.9, 127.6, 123.4, 122.9, 122.2,
121.3, 119.2, 117.3, 49.5.
Typical procedure for the synthesis of 3,4-disubstituted isoxazol-5(4H)-ones
(7a-s)
A mixture of hydroxylamine hydrochloride 5 (0.0695 g, 1 mmol), b-oxoeser 6
(1 mmol), and 2-HSBA (15 mol%) in 4 mL of distilled water was stirred at room
temperature for 15 min, then aromatic aldehyde 2 (1 mmol) was added to the
mixture. The reaction mixture was stirred at RT until the reaction was completed.
The reaction was monitored by TLC analysis up to the starting materials were
consumed completely and the final product spot was not changed. After completion
of the reaction, the precipitate was separated by simple filtration, and washed with
cold distilled water and dried in the air. Crude products were recrystallized from
ethanol (95 %) to afford the title pure compounds. The HSBA is soluble in water
and ethanol. After removal of the solvent from the filtrate by evaporation, the
catalyst is recovered and reused for the subsequent reactions. The identity of the
known products was confirmed by comparison of their spectroscopic data and
physical properties with those available in recent papers [68–85]. Spectral data for
7i and 7q were as follows:
N-(4-((3-methyl-5-oxoisoxazol-4(5H)-ylidene)methyl)phenyl)acetamide (7i)
1H NMR (400 MHz, DMSO-d6): d = 10.51 (s, 1H), 8.47 (d, J = 9.2 Hz, 2H), 7.85
(s, 1H), 7.78 (d, J = 8.8 Hz, 2H), 2.28 (s, 3H), 2.12 (s, 3H); 13C NMR (100 MHz,
DMSO-d6): d = 170.1, 162.9, 151.5, 145.2, 136.2, 127.4, 118.8, 116.5, 24.8, 11.8.
123

2-Hydroxy-5-sulfobenzoic acid
3-(chloromethyl)-4-(4-(diethylamino)-2-hydroxybenzylidene)isoxazol-5(4H)-one
(7q)
1H NMR (400 MHz, DMSO-d6): d = 11.08 (s, 1H), 9.14 (d, J = 9.6 Hz, 1H), 8.07
(s, 1H), 6.52 (dd, J = 2.0, 9.6 Hz, 1H), 6.18 (d, J = 2.4 Hz, 1H), 3.50 (q, J = 6.8,
7.2 Hz, 4H), 1.17 (t, J = 6.8, 7.2 Hz, 6H); 13C NMR (100 MHz, DMSO-d6):
d = 170.9, 164.2, 162.2, 156.4, 143.1, 136.1, 111.9, 106.9, 101.2, 95.8, 45.2, 36.4,
13.1.
Results and discussion
At a first step, in order to find the best optimal reaction conditions, three-component
condensation of 2-naphthol (1a), benzaldehyde (2a) and acetamide (3a) was
employed as the template reaction. Different amounts of 2-HSBA as the catalyst as
well as reaction temperature were screened using the template reaction under
solvent-free reaction conditions (SFRCs). The results are shown in Table 1. By
carrying out the template reaction at 100 °C without a catalyst, no product was
formed even after heating for 2 h (entry 1). When 5 mol% loading of catalyst was
applied for this condensation, it was observed that the corresponding product 4a was
formed in 82 % yield (entry 2). The product formation in the presence of the
catalyst upon heating indicates that the presence of a catalyst for this reaction is
necessary. In addition, when catalyst loading was increased to 10 mol%; the
reaction was completed within 8 min and up to 95 % yield of the desired product 4a
was obtained (entry 3). The use of higher amounts of catalyst did not improve the
results (entries 4 and 5). Hence, this amount of catalyst is sufficient to promote the
reaction. The effect of temperature on the synthesis of 4a was also investigated in
the presence of 10 mol% 2-HSBA loading (entries 6 and 10). It was found that the
best results were obtained at 100 °C. At temperatures lower than 100 °C, the yield
of the product sharply decreased even with longer reaction times (entries 6 and 8).
The increase in temperature leads to a decrease in the yield of the product (entries 9
and 10). 2-HSBA shows excellent catalytic activity toward this Betti-3CR. It was
concluded that implementating the reaction under SFRCs at 100 °C is the optimal
condition for the Betti-3CR in the presence of 10 mol% of the catalyst.
Screening of other acidic reagents such as polyphosphoric acid, cinnamic acid,
terephthalic acid, isophthalic acid, ascorbic acid, and methanesulfonic acid, was also
tested (Table 2). Only trace products were detected in the presence of polyphos-
phoric acid, cinnamic acid, and terephthalic acid (entries 1–3). In the other cases,
the yield and reaction times were not satisfactory compared with the PISA (entries
4–6).
To check the effect of solvent on the yield of the product, the template reaction
was also carried out in various solvents (Table 3). Markedly low yields were
observed when EtOH, H2O, CH2Cl2, EtOAc, or CH3CN were utilized as the
reaction media (entries 1–5).
To study the applicability of the method, the 3CR of 2-naphthol (1) with amides
and a series of structurally diverse substituted benzaldehydes (2a–o) were
123

H. Kiyani et al.
Table 1 Effect of the amounts of the catalyst and reaction temperature on the synthesis of N-((2-
hydroxynaphthalen-1-yl)(phenyl)methyl)acetamide (4a) as a template in the SFRC
H
C
3
O
H
O
H
O
NH
O
H
O
+
+
H2N
H
C
3
1
2a
3a
4a
Entry
Catalyst (mol%)
Temp. (°C)
Time (min)a
Yield (%)b
1
–
5
100
100
100
100
100
50
120
20
8
–
82
95
90
90
60
84
90
92
92
2
3c
10
15
20
10
10
10
10
10
4
8
5
5
6
25
20
15
8
7
80
8
90
9
110
120
10
8
Reaction conditions: a well-ground mixture of 1-naphthol 1 (1 mmol), benzaldehyde 2a (1 mmol),
acetamide 3a (1 mmol), and the catalyst (2-HSBA) was magnetically stirred
a
Progress of the reaction was monitored with TLC analysis
b
Isolated yields
c
Optimized conditions shown in bold
conducted under the optimal reaction conditions. Representative results are listed in
Table 4. The reaction of benzaldehyde substituted with the electron-withdrawing
group occurred at a higher yield and shorter reaction time than its electron-donating
counterpart. Sterically hindered aryl aldehydes (entries 4, 6, 8, 12, 17, 19 and 20),
such as 2-nitrobenzaldehyde (2d), 2-chlorobenzaldehyde (2f), 2,4-dichlorobanzal-
dehyde (2h) and 2,5-dimethoxybenzaldehyde (2l), also reacted with 2-naphthol (1)
and amides (3a, b) to give the corresponding 1-amidoalkyl-2-naphthols in excellent
yields, although in some cases the reactions proceeded rather slowly. The use of
urea (3c) in the synthesis of the title compounds also gave similar results (entries
26–30). The reaction of 2-naphthol (1) and acetamide (3a) was also performed
under the same optimal reaction conditions in the presence of an aliphatic aldehyde,
n-butyraldehyde; however, no corresponding amidoalkyl naphthol product was
observed after 20 h. In addition, a reaction of 2-naphthol (1) and acetamide (3a)
with a,b-unsaturated aldehydes (a-methylcinnamaldehyde and cinnamaldehyde)
was implemented and did not lead to product formation after 20 h. On the other
hand, the reaction of 2-naphthol (1) and acetamide (3a) with hetero-aromatic
aldehydes such as furan-2-carbaldehyde and thiophene-2-carbaldehyde led to
corresponding products with 60 and 70 % yields, respectively. This approach was
highly operative for the preparation of targeted compounds (4a–ad) as well as, in all
123

2-Hydroxy-5-sulfobenzoic acid
Table 2 The synthesis of N-((2-hydroxynaphthalen-1-yl)(phenyl)methyl)acetamide (4a) using various
catalysts
H
C
3
O
H
O
NH
OH
O
OH
+
+
H2N
CH3
1
2a
3a
4a
Entry
Catalyst (mol%)
PPAc (10, 15, 20)
Time (min)a
Yield (%)b
1
2
3
4
5
6
120
120
120
27
Trace
Trace
Trace
75
Cinnamic acid (10, 15, 20)
Terephthalic acid (10, 15, 20)
Isophthalic acid (15)
Ascorbic acid (20)
60
50
Methanesulfonic acid (15)
30
80
Reaction conditions: a well-ground mixture of 1-naphthol 1 (1 mmol), benzaldehyde 2a (1 mmol),
acetamide 3a (1 mmol), and the catalyst was magnetically stirred at 100 °C
a
Progress of the reaction was monitored with TLC analysis
b
Isolated yields
c
Polyphosphoric acid
Table 3 The synthesis of N-((2-hydroxynaphthalen-1-yl)(phenyl)methyl)acetamide (4a) using various
solvents
H
C
3
O
H
O
NH
OH
O
+
OH
+
H2N
CH3
1
2a
3a
4a
Entry
Solvent
Time (min)a
Isolated yield (%)
1
2
3
4
5
6
EtOH
H2O
60
60
60
60
60
8
50
48
30
40
55
95
CH2Cl2
EtOAc
CH3CN
–
Reaction conditions: a well-ground mixture of 1-naphthol 1 (1 mmol), benzaldehyde 2a (1 mmol),
acetamide 3a (1 mmol), and 2-HSBA (10 mol%) was magnetically stirred at 100 °C
a
Progress of the reaction was monitored with TLC analysis
123

H. Kiyani et al.
Table 4 The 3C synthesis of 1-amidoalkyl-2-naphthols (4a–ad) catalyzed by 2-HSBA under SFRCs at
100 °C
Z
O
H
O
R
O
NH
2-HSBA
(10 mol%)
H
O
+
+
H2N
Z
H
O
Solvent-free, 100 ºC
R
1
2a-o
3a-c
(1 mmol)
4a-ad
(1 mmol)
(1 mmol)
Entry
R
Z
Product Time (min) Yield (%)a Mp (°C)
Observed Reported [ref.]
1
H (2a)
CH3 (3a) 4a
CH3 (3a) 4b
CH3 (3a) 4c
CH3 (3a) 4d
CH3 (3a) 4e
CH3 (3a) 4f
CH3 (3a) 4g
CH3 (3a) 4h
CH3 (3a) 4i
CH3 (3a) 4j
CH3 (3a) 4k
CH3 (3a) 4l
CH3 (3a) 4m
8
5
95
93
90
91
91
92
90
93
88
87
80
88
85
97
96
95
95
93
92
97
90
85
81
90
241–244 228–230 [41]
239–242 236–238 [41]
265–269 241–243 [41]
180–182 181–183 [41]
236–239 236–238 [41]
210–211 195–197 [41]
230–232 232–233 [42]
230–231 225–226 [41]
219–221 220–222 [42]
184–185 164–168 [41]
204–205 203–205 [41]
253–257 252–254 [41]
218–219 226–227 [10]
230–231 237–239 [19]
237–238 238–240 [26]
233–235 234–236 [26]
266–269 262–264 [26]
183–184 186–188 [26]
266–268 264–266 [26]
240–242 235–236 [30]
200–202 202 [25]
2
4-NO2 (2b)
3-NO2 (2c)
2-NO2 (2d)
4-Cl (2e)
3
10
7
4
5
5
6
2-Cl (2f)
15
20
4
7
4-F (2g)
8
2,4-(Cl)2 (2h)
4-CH3 (2i)
4-OCH3 (2j)
3-OCH3 (2k)
9
15
20
15
25
30
6
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
3,5-(OCH3)2 (2l)
4-OH (2m)
H (2a)
Ph (3b)
Ph (3b)
Ph (3b)
Ph (3b)
Ph (3b)
Ph (3b)
Ph (3b)
Ph (3b)
Ph (3b)
Ph (3b)
Ph (3b)
4n
4o
4p
4q
4r
4s
4-NO2 (2b)
3-NO2 (2c)
2-NO2 (2d)
4-Cl (2e)
3
5
4
3
2-Cl (2f)
5
2,4-(Cl)2 (2h)
4-CH3 (2i)
4-OCH3 (2j)
3-OCH3 (2k)
4t
2
4u
4v
4w
4x
10
10
8
208–210 208–210 [26]
210–214 232 [25]
3-OCH3-4-OH
(2n)
30
219–221 223–225 [108]
25
26
27
28
29
30
a
4-N(CH3)2 (2o)
H (2a)
Ph (3b)
4y
30
10
7
82
95
96
95
90
91
218–224 221 [25]
NH2 (3c) 4z
NH2 (3c) 4aa
NH2 (3c) 4ab
NH2 (3c) 4ac
NH2 (3c) 4ad
178–182 176–178 [26]
190–193 192–194 [26]
190–192 192–194 [26]
168–170 166–168 [26]
115–117 118–120 [42]
4-NO2 (2b)
3-NO2 (2c)
4-Cl (2e)
8
5
4-CH3 (2i)
20
Isolated yields
123

2-Hydroxy-5-sulfobenzoic acid
Table 5 Effect of the amounts of the catalyst and reaction temperature on the synthesis of 4-(4-hydroxy-
3-methoxybenzylidene)-3-methylisoxazol-5(4H)-one (7h) as a template in the water
O
H3CO
C O
H
OH
H2O (4 mL)
.
NH2OH HCl
+
+
OCH3
N
H
O
O
O
O
O
2n
5
6a
(1 mmol)
7h
(1 mmol)
(1 mmol)
Entry
Catalyst (mol%)
Temp. (°C)
Time (min)a
Yield (%)b
1
–
RT
RT
RT
RT
RT
RT
50
120
120
120
90
55
72
80
90
96
95
50
40
35
5
2
2.5
5
3
4
5c
10
15
20
15
15
15
15
70
6
70
7
70
8
75
70
9
100
120
70
10
70
Reaction conditions: vanillin 2n (1 mmol), hydroxylamine hydrochloride 5 (1 mmol), ethyl acetoacetate
6a (1 mmol), solvent (4 mL) and the 2-HSBA was magnetically stirred at room temperature
a
Progress of the reaction was monitored with TLC analysis
b
Isolated yields
c
Optimized conditions shown in bold
Table 6 The synthesis of 4-(4-hydroxy-3-methoxybenzylidene)-3-methylisoxazol-5(4H)-one (7h) using
various solvents
O
H3CO
CHO
H
O
2-HSBA
NH2OH.HCl
+
+
OCH3
N
H
O
O
O
O
O
2n
5
6a
7h
Entry
Solvent
Time (min)a
Isolated yield (%)
1
2
3
4
5
6
7
EtOH
120
120
180
120
120
100
120
67
42
50
54
61
73
30
Acetone
1,4-Dioxane
n-Hexane
CH2Cl2
EtOH:H2O (1:1)
No solvent
Reaction conditions: vanillin 2n (1 mmol), hydroxylamine hydrochloride 5 (1 mmol), ethyl acetoacetate
6a (1 mmol), solvent (4 mL), and 2-HSBA (15 mol%) was magnetically stirred at room temperature
a
Progress of the reaction was monitored with TLC analysis
123

H. Kiyani et al.
Table 7 The 3C synthesis of 3,4-disubstituted isoxazol-5(4H)-ones (7a-s) catalyzed by 2-HSBA under
aqueous media at room temperature
O
H
Ar
X
X
2-HSBA
(15 mol%)
NH2OH.HCl
+
+
Ar
O
Water, RT
N
O
O
O
O
2
5
6a-b
7a-s
(1 mmol)
(1 mmol)
(1 mmol)
Entry
Ar
X
Product
Time
(min)
Yield
(%)a
Mp (°C)
Observed
Reportedb
1
C6H5 (2a)
H (6a)
H (6a)
H (6a)
H (6a)
H (6a)
H (6a)
H (6a)
H (6a)
H (6a)
H (6a)
H (6a)
Cl (6b)
Cl (6b)
Cl (6b)
Cl (6b)
Cl (6b)
Cl (6b)
Cl (6b)
H (6a)
7a
7b
7c
7d
7e
7f
110
75
80
70
85
120
85
70
75
50
60
110
75
65
70
75
80
70
85
87
95
92
95
90
88
93
96
90
94
88
85
92
92
89
92
90
89
93
141–142
135–136
174–175
211–213
200–201
198–199
225–227
216–217
188–191
144–146
145–146
183–184
130–133
182–185
179–181
141–143
203–207
147–148
174–176
140–142
135–136
175–177
210–211
199–201
198–200
220–221
213–215
New
2
4-CH3C6H4 (2i)
3
4-OCH3C6H4 (2j)
4-OHC6H4 (2m)
4
5
3-OHC6H4 (2p)
6
2-OHC6H4 (2q)
7
4-N(CH3)2C6H4 (2o)
3-OCH3-4-OHC6H3 (2n)
4-NH-COCH3C6H4 (2r)
2-Thienyl (2s)
7g
7h
7i
8
9
10
11
12
13
14
15
16
17
18
19
a
7j
143–145
142–144
182–183
175–177
183–186
179–180
142–145
New
3-Thienyl (2t)
7k
7l
C6H5 (2a)
4-OCH3C6H4 (2j)
4-OHC6H4 (2m)
7m
7n
7o
7p
7q
7r
7s
4-N(CH3)2C6H4 (2o)
3-OCH3-4-OHC6H3 (2n)
2-OH-4-N(Et)2C6H3 (2u)
2-Thienyl (2s)
146–148
173–178
C6H5CH=CH (2v)
Isolated yields
b
Melting points are listed in Refs. [77–85]
cases, 1-amidoalkyl-2-naphthols were the sole products and no by-products were
observed.
After the successful synthesis of a series of 1-amidoalkyl-2-naphthols, we turned
our attention toward the synthesis of 3,4-disubstituted isoxazol-5(4H)-ones in the
presence of 2-HSBA (Scheme 2).
Treatment of 2n with hydroxylamine hydrochloride (5), ethyl acetoacetate (6a),
and 10 mol% of 2-HSBA at room temperature in H2O led to the 4-(4-hydroxy-3-
methoxybenzylidene)-3-methylisoxazol-5(4H)-one (7h) in 90 % yield for 90 min
(Table 5, entry 4). This reaction was selected as a template reaction and the results
are summarized in Tables 5 and 6. When 15 mol% of 2-HSBA was used, the
desired product was obtained in 96 % yield after 70 min. The reaction in the
123

2-Hydroxy-5-sulfobenzoic acid
O
H
H
O
H
H
H
O
Ar
H
O
H
H3O+ from 2-HSBA
Ar
2a-o
H
H
O
O
Nucleophilic addition
1
-H2O
Ar
R
O
O
Ar
NH
R
NH2
3a-c
O
H
O
Michael addition
ortho-quinone methides
(o-QMs)
4a-ad
Scheme 3 The proposed mechanism for the formation of 1-amidoalkyl-2-naphthols (4a–ad)
H
O
H
O
HO
O
O
O
N
O
N
NH2OH
X
X
X
O
O
-
H
2O
H
C
6
D
O
H
H
H
H
O
H3O+ from 2-HSBA
2
Ar
knoevenagel condensation
H
HO
HO
N
H
H
O
O
O
O
N
X
N
r
O
O
Intramolecular
Z
X
O
-H2O
O-attack cyclization
Ar
OH
Ar
G
A
F
E
H
O
O
N
Ar
X
X
O
- EtOH
N
O
O
Ar
H
7a-s
Scheme 4 The proposed mechanism for the formation of 3,4-disubstituted isoxazol-5(4H)-ones (7a-s)
absence of a catalyst afforded 7h in 55 % yield at longer reaction times (Table 5,
entry 1). Using lower amounts of 2-HSBA, the reaction proceed in moderate yields
(Table 5, entries 2 and 3). The use of higher amounts of catalyst did not improve the
yield and reaction times (Table 5, entry 6). Performing the reaction at higher
123

H. Kiyani et al.
Table 8 Reusability of
2-HSBA in the synthesis of 4a
Catalyst recycle
Time (min)
Isolated yield (%)
Fresh
5
5
95
90
84
80
70
1
2
3
4
6
The reaction conditions are
similar to the optimized
8
conditions described for the
template reaction in Table 1
10
Table 9 Reusability of
2-HSBA in the synthesis of 7h
Catalyst recycle
Time (min)
Isolated yield (%)
Fresh
70
75
94
88
79
71
1
2
3
The reaction conditions are
similar to the optimized
90
conditions described for the
template reaction in Table 5
150
temperatures using 2-HSBA as the catalyst did not afford satisfactory results
(Table 5, entries 7–10). The effect of various solvents including EtOH, acetone, 1,4-
dioxane, n-hexane, CH2Cl2, and a mixture of ethanol–water (EtOH:H2O, V:V) was
also explored (Table 6). In these cases, the use of other solvents rather than water
resulted in low reaction yields (entries 1–6). Under solvent-less conditions, no
obvious improvement of the reaction was observed (entry 7). Therefore, water was
the most effective solvent in this reaction. In terms of catalyst amounts, temperature
and solvent effects, the use of 15 mol% of the catalyst, room temperature and water
were selected as the optimized reaction conditions for the present reaction.
With the optimized reaction conditions in hand, the generality of this reaction
then examined, as shown in Table 7. A range of aryl aldehyde derivatives with
different substituents on the benzene ring were reacted with hydroxylamine
hydrochloride (5) and b-oxoesters (6a, b) smoothly to give the corresponding 3,4-
disubstituted isoxazol-5(4H)-ones (7a–s) in good to high yields. The reaction was
clean, and no chromatographic separation was performed because no impurities
were observed. These results show that aromatic aldehydes bearing electron-
donating functional groups proved to be good substrates and reacted smoothly. It
seems that substituents at ortho-position on the phenyl ring had a slight effect on
the yields and reaction times (entries 6, 9 and 21). Containing 2-thienyl and
3-thienyl, heterocyclic substrates both can be converted to the desired products in
94, 88 and 89 % yields, respectively (entries 10–11, and 18). Also, a reaction of
ethyl acetoacetate (6a) and hydroxylamine hydrochloride (5) with a,b-unsaturated
aldehydes such as cinnamaldehyde was implemented and lead to product
formation with high yield (entry 19). Not successful, attempts to conduct the
reaction with the electron-withdrawing groups on the phenyl ring and aliphatic
aldehydes.
The possible reaction mechanism for the green formation of 1-amidoalkyl-2-
naphthol products (4a–ad) can be presented in Scheme 3. This process could
123

2-Hydroxy-5-sulfobenzoic acid
Table 10 Comparison of the catalytic performance of catalyst 2-HSBA for the one-pot 3CR of
2-naphthol (1), 3-nitrobenzaldehyde (2c), and benzamide (3b) with those obtained by reported catalysts
H
O
O
O
H
+
O
NH
Catalyst
H2N
N
O2
+
Conditions
H
O
N
O2
1
2c
3b
4p
Entry
Catalyst (mol%) [g]/conditions
Time (min)
Yield (%)
References
1
[Msim]Cl (10)/SF, 120 °C
Maltose (20)/SF, 100 °C
[2-MPyH]OTf (5)/SF, 125 °C
Sulfanilic acid (20)/SF, MW
5
18
20
8
90
90
96
89
88
95
95
90
94
93
97
88
95
[19]
2
[26]
3
[41]
4
[27]
5
Sulfanilic acid (20)/SF, 110–120 °C
TCT (5)/SF, 100 °C
MSI (6)/ionic liquid [Bpy]BF4, 80 °C
DPA (10)/SF, 90 °C
PEG1000-DAIL (0.03 mmol)/80 °C
[MIMPS]H2PMo12O40 (10)/SF, 110 °C
[Dsim]HSO4 (5)/SF, 80 °C
14
20
25
20
5
[27]
6
[42]
7
[30]
8
[40]
9
[33]
10
11
12
13
5
[37]
20
360
5
[35]
PSSA-NKC-9 [0.17]/chloroform, reflux
[34]
2-HSBA (10)/SF, 100 °C
Present work
[Msim]Cl 3-methyl-1-sulfonic acid imidazolium chloride; SF solvent-free; [2-MPyH]OTf 2-methylpy-
ridinium trifluoromethanesulfonate; TCT 2,4,6-trichloro-1,3,5-triazine; MSI 1-methyl-3-(2-(sulfo-
oxy)ethyl)-1H-imidazol-3-ium chloride; [Bpy]BF4 N-butylpyridinium tetrafluoroborate; DPA
dodecylphosphonic acid; PEG1000-DAIL PEG-based dicationic acidic ionic liquid; [Dsim]HSO4 1,3-
disulfonic acid imidazolium hydrogen sulfate; PSSA-NKC-9 polymer-supported sulphonic acid NKC-9
proceeds via formation of ortho-quinone methides (o-QMs) [19, 35, 39] between
2-naphthol (1) and the substituted benzaldehydes (2a–o), assisted by catalyst. Then, the
Michael additionofamides(3a, b orurea, 3c) totheortho-QMsoffersthe 1-amidoalkyl-
2-naphthols. The acidic functional groups of 2-HSBA could provide acidic site for
activating substituted benzaldehydes efficiently, so facilitating this 3-CR.
Based on the literature [68–85], the following mechanism also proposed for the
3C synthesis of 3,4-disubstituted isoxazol-5(4H)-ones (7a–s) (Scheme 4). It is
reasonable to assume that oxime derivatives C were formed by the condensation
reaction of hydroxylamine hydrochloride with b-ketoester 5. Then the Knoevenagel
adducts F were formed through the condensation of intermediate C and protonated
aryl aldehyde 2. The next step may involve intramolecular O-attack cyclization of
F to cyclic derivatives G, which undergoes a proton exchange, followed by H is
deethanolized to target products 7a–s.
The reusability of the 2-HSBA was also studied (Tables 8, 9). The catalyst was
recovered after each run and reused for subsequent cycles (Table 8). It showed nearly
the same activity but with a slight decrease of yield. The decreasing of the yield of the
123

H. Kiyani et al.
Table 11 Comparison of the catalytic performance of catalyst 2-HSBA for the one-pot 3CR of p-
methylbenzaldehyde (2i), hydroxylamine hydrochloride (5), and ethyl acetoacetate (6b) with those
obtained by reported catalysts
O
CHO
Me
Catalyst
NH2OH.HCl
+
+
Conditions
Me
N
O
O
O
O
2i
5
6a
7b
Entry
Catalyst (mol%)/conditions
Time (min)
Yield (%)
References
1
Sodium benzoate (10)/H2O, RT
Na2S (5)/EtOH, RT
90
90
90
60
180
48
15
70
60
50
50
240
50
70
75
87
88
[68]
2
[69]
3
Sodium silicate (5)/H2O, RT
Pyridine (100)/H2O, US
91
[70]
4
82
[74]
5
Pyridine (100)/EtOH, reflux
Catalyst free/grinding
71.4
61
[77]
6
[78]
7
Catalyst free/105–110 °C
Sodium ascorbate (5)/H2O, RT
Sodium citrate (10)/H2O, RT
Sodium saccharin (10)/H2O, RT
Sodium tetraborate (10)/H2O, RT
Sodium azide (5)/H2O, RT
Boric acid (10)/H2O, RT
PPI (10)/H2O, RT
66.3
95
[78]
8
[79]
9
91
[80]
10
11
12
13
14
15
91
[81]
95
[82]
85
[83]
92
[84]
96
[85]
2-HSBA (15)/H2O, RT
95
Present work
RT room temperature, US ultrasound
product is probably related to a slight decrease in the catalytic activity of the catalyst or
could be attributed to the loss of catalyst recovery in the course of the reaction. In
addition, Table 9 shows that the catalytic was recycled and reused three times.
The benefit of the catalyst and comparison of the efficiency of the 2-HSBA
catalyst with other catalysts in the synthesis of 1-amidoalkyl-2-naphthols and 3,4-
disubstituted isoxazol-5(4H)-ones are indicated in Tables 10 and 11. It is clear from
these data that 2-HSBA is comparable to the formerly reported approaches in terms
of reaction times and yields. Contrasting some of the previous reported methods,
this procedure does not require any additives, ionic liquids or hazardous solvents
such as chloroform in the synthesis of 1-amidoalkyl-2-naphthols. In addition,
according to Table 11, there is no need for bases such as pyridine, heating or special
devices such as ultrasound.
Conclusions
In summary, the present methodology is a green, simple, and environmentally
benign protocol to access a series of 1-amidoalkyl-2-naphthols and 3,4-disubstituted
123

2-Hydroxy-5-sulfobenzoic acid
isoxazol-5(4H)-ones in high yields and shorter reaction times. The 3CR are
conducted under thermal SFRCs yielding the corresponding Betti analogue
compounds. It was also found that 3CR of aryl aldehydes, hydroxylamine
hydrochloride, and ethyl acetoacetate (or ethyl 4-chloroacetoacetate) can be
significantly performed to achieve the 3,4-disubstituted isoxazol-5(4H)-ones at
room temperature. 2-HSBA displays excellent catalytic activity toward these 3CRs.
The use of 2-HSBA in these 3CRs has benefits such as clean reaction profiles, lack
of side reactions, green, minimization of waste, simple experimental procedure,
recyclability of the catalyst, simplicity of operation, and easy work-up.
Acknowledgment The authors are grateful to Damghan University Research Council.
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