One-pot synthesis of 1-amidoalkyl-2-naphthols under solvent-free conditions

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Organic Preparations and Procedures
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One-pot Synthesis of 1-Amidoalkyl-2-
naphthols under Solvent-free Conditions
Behrooz Malekia & Fereshteh Taimazia
a Department of Chemistry, Hakim Sabzevari University Sabzevar,
Khorasan, Iran
Published online: 27 May 2014.
To cite this article: Behrooz Maleki & Fereshteh Taimazi (2014) One-pot Synthesis of 1-Amidoalkyl-2-
naphthols under Solvent-free Conditions, Organic Preparations and Procedures International: The New
Journal for Organic Synthesis, 46:3, 252-260, DOI: 10.1080/00304948.2014.903143
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Organic Preparations and Procedures International, 46:252–260, 2014
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5453 online
DOI: 10.1080/00304948.2014.903143
One-pot Synthesis of 1-Amidoalkyl-2-naphthols
under Solvent-free Conditions
Behrooz Maleki and Fereshteh Taimazi
Department of Chemistry, Hakim Sabzevari University Sabzevar, Khorasan, Iran
Compounds bearing 1,3-amino-oxygenated functional groups are present in a variety of
biologically important natural products and potent drugs including a number of nucleoside
antibiotics and HIV protease inhibitors, such as ritonavir and lipinavir.1–4 1-amidoalkyl-
2-naphthols can be easily hydrolyzed to 1-aminoalkyl-naphthols, which show biological
activities such as hypertensive and bradycardiac effects.5–11
In multi-component reactions (MCRs), one can create highly complex molecules in
a single reaction from readily available starting materials often without purification; thus,
MCRs are time-effective and economically favorable processes in diversity generation.12,13
We previously reported the in situ generation of ortho-quinone methides (o-QMS) which
further combine with β-naphthols to give 14H-dibenzo[a,j]xanthene derivatives.14,15 The
present report describes the reaction of o-QMS with other nucleophiles such as amides for
the synthesis of 1-amidoalkyl-2-naphthol derivatives (Scheme 1).
Ar
NHCOR1
OH
OH
NaCl/1100C
ArCHO
+
+ R1CONH2
R1 = CH3,Ph
or
NBPI or TCCA/1000C
Solvent-Free
1
2
3
4
Scheme 1
Due to their diverse biological activities, the synthesis of 1-amidoalkyl-2-naphthols has
attracted considerable attention. So far several alternative and efficient methods have been
developed for the synthesis of 1-amidoalkyl-2-naphthols by MCRs of β-naphthols, alde-
hydes, amides or ureas or acetonitriles in the presence of catalysts such as p-TSA,16 mont-
morillonite K10,17 indion-130,18 ZrOCl2,19 N-bromosuccinimide (NBS),20 Fe(HSO4)3,21
silica gel-supported polyphosphoric acid,22 2,4,6-trichloro-1,3,5-triazine,23,24 thiamine
Received April 26, 2013; accepted January 3, 2014.
Address correspondence to Behrooz Maleki, Department of Chemistry, Hakim Sabzevari Uni-
versity, Sabzevar, Khorasan, Iran. E-mail: malekibehrooz@gmail.com
252

Synthesis of 1-Amidoalkyl-2-naphthols
253
hydrochloride,25 NaHSO4.SiO2,26 P2O5,27 SnCl2.2H2O,28 silphox [POCl3-n(SiO2)n] or
silphos [PCl3-n(SiO2)n]29 Cu(ClO4)2.6H2O,30 heteropoly acids,31–33 oxalic acid,34 molten
4-(1-imidazolium) butane sulfonate,35 trityl chloride,36 InCl3,37 TBBDA,38 silica chloride,39
and copper p-toluenesulfonate.40 However, some of these protocols suffer from certain
drawbacks, such as highly acidic and expensive catalysts, the use of toxic organic solvents,
and tedious work-up procedures. Thus, there is a need for the development of alternatives
for the production of 1-amidoalkyl-2-naphthol derivatives, which may overcome those
limitations.
Sodium chloride is inexpensive, safe, green, and non-corrosive41; it is therefore of inter-
est to examine the behavior of sodium chloride as catalyst in the synthesis of 1-amidoalkyl-
2-naphthol derivatives. To the best of our knowledge, the generality and applicability of
sodium chloride in the preparation of 1-amidoalkyl-2-naphthol derivatives has not been
reported. In connection with our ongoing research for the development of simple and ef-
ficient synthetic methodologies,42–45 we now report an efficient, eco-friendly, safe, green,
and practical method for the three-component synthesis of 1-amidoalkyl-2-naphthol deriva-
tives using NaCl or N-bromophthalimide (NBPI) or trichloroisocyanuric acid (TCCA) as a
catalyst (Scheme 1).
Over past decades, solvent-free reactions have seen many applications in organic
synthesis. These processes are not only environmentally benign, but also economically
beneficial because toxic wastes can be minimized or eliminated, so the costs of waste
treatment are reduced. An additional attractive feature is their operational simplicity.46–52
To choose optimum conditions, the effect of temperature on the rate of the reac-
tion was first studied for the preparation of 1-amidoalkyl-2-naphthols from MCRs of
2-naphthol (1 mmol), benzaldehyde (1 mmol), and benzamide (1.2 mmol) under solvent-
free conditions. Next, the study set out to determine the optimal amount of NaCl by
varying the amount of the NaCl. The catalytic efficiency of LiBr and KBr in the reaction
was also studied under solvent-free conditions at 110◦C. NaCl was the best catalyst. Al-
though, it is known that Li+ is a better oxophile than Na+, our studies showed that KCl
and NaCl behaved similarly and gave the conversion under similar reaction conditions.
This result could be explained by the considerably lower solubility of LiCl than NaCl
in the reaction medium. None of the desired product was detected in the absence of the
catalyst.
After optimization of the reaction conditions, we studied the generality of these con-
ditions to other substrates. Using this method, different aldehydes were reacted with β-
naphthol to produce the corresponding 1-amidoalkyl-2-naphthols under solvent-free con-
ditions (Table 1). All the reactions proceeded efficiently within 30–100 min at 110◦C
to provide the corresponding 1-amidoalkyl-2-naphthol derivatives in good yields ranging
from 74% to 86%. It was shown that aromatic aldehydes bearing electron-withdrawing
groups reacted more rapidly than those aldehydes with electron-donating groups. In our
preliminary attempts with benzaldehyde, 2-naphthol, and urea, the reaction failed to yield
the corresponding aminoalkyl naphthols and a mixture of products was obtained and the
desired products could not be isolated.
We also investigated the use of N-bromophthalimide (NBPI) and 1,3,5-trichloro-
2,4,6-triazinetrione (trichloroisocyanuric acid or TCCA). The use of NBPI and
TCCA as powerful catalysts for organic transformations has been reported.53–56 Also,

254
Maleki and Taimazi
Table 1
Synthesis of 1-Amidoalkyl-2-naphthol in the Presence of NBPI (10 mol%), TCCA
(2.5 mol%), and NaCl under Solvent-free Conditions
mp (◦C)
Yielda (%) Time (min)
Product (4)
Ar
C6H5
4-ClC6H4
2-ClC6H4
R1
I-II-III
I-II-III
Found
Lit.
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
82-90-84
84-88-80
83-80-75
80-81-86
94-90-82
90-90-82
78-80-75
88-86-78
84-88-77
82-86-78
86-90-75
84-84-74
80-83-81
78-87-82
80-86-84
77-86-75
82-86-78
80-88-75
84-82-76
85-89-74
82-89-75
75-73-75
75-25-50
75-35-60
50-40-40
40-40-35
40-30-30
30-30-30
50-60-100
70-60-50
30-20-80
30-30-90
20-20-70
25-25-80
50-55-80
50-40-60
45-45-50
75-60-70
50-40-60
40-35-80
40-40-90
45-35-60
35-30-90
40-40-100
236–238 234–236
188–190 187–188
284–285 284–285
266–268 266–267
228–229 228–229
210–212 214–216
214–216 216–217
186–188 182–184
197–198 193–194
267–268 266–267
214–216 214–216
2-NO2C6H4
4-NO2C6H4
3-NO2C6H4
4-CH3C6H4
4-BrC6H4
4-FC6H4
2-MeOC6H4
3-MeOC6H4
4-MeOC6H4
C6H5
4-NO2C6H4
3-NO2C6H4
4-FC6H4
4-BrC6H4
2-ClC6H4
Ph
Ph
Ph
204–206
208-209
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
239–240 241–243
245–247 247–249
238–240 235–237
228–229 230–232
230–232 228–230
213–215 213–215
199–201 198–199
224–227 223–225
203–205 202–204
220–221 220–222
2,4-ClC6H4
4-ClC6H4
3-MeOC6H4
4-MeC6H4
4t
4u
4v
aThe yields and times by NBPI (I), TCCA (II), and NaCl (III).
1,3,5-trichloro-2,4,6-triazinetrione has traditionally found applications in analytical chem-
istry as complexation agent, in electrochemistry in multi-step redox systems and as a beach-
ing agent, disinfectant, bactericide, and pesticide or herbicide component in agriculture.57
We used NBPI instead of NaCl under the same conditions (Scheme 1). In order to explore
the feasibility of this synthetic methodology for 1-amidoalkyl-2-naphthol derivatives, the
reaction was first carried out by simple mixing of β-naphthol (1 mmol), benzaldehyde
(1 mmol), and benzamide (1.2 mmol) under solvent-free conditions in the presence of
10 mol% of NBPI. The mixture was stirred at 100◦C for 75 min and the correspond-
ing product (4a) was obtained in 82% yield. Encouraged by this result, we investigated
the amount of NBPI and the temperature of reaction; the best result was obtained with
10 mol% of NBPI under solvent-free conditions at 100◦C. The results are summarized in
Table 2.

Synthesis of 1-Amidoalkyl-2-naphthols
255
Table 2
Optimizing the Reaction Conditions
Entry
Catalyst (mol%)
Temperature (◦C)
Time (min)
Yield (%)
1
2
3
4
5
6
10
15
5
10
10
10
100
100
100
110
90
75
75
160
75
75
160
82
79
75
78
75
52
85
Several structurally diverse aldehydes (4a–v) (Table 1) were subjected to condensation
with β-naphthol and amide compounds under the catalytic influence of NBPI (10 mol%)
and solvent-free conventional heating, and 1-amidoalkyl-2-naphthols were obtained in high
yields. In all cases, amidoalkyl naphthols were the sole products and no by-product was
observed. Aromatic aldehydes carrying electron-withdrawing groups reacted more rapidly
than those bearing electron-donating groups.
Finally, we have developed this synthetic method by using trichloroisocyanuric acid
(TCCA) for 1-amidoalkyl-2-naphthol derivatives. To achieve the optimal reaction condi-
tions, the reaction of 4-chlorobenzaldehyde (1 mmol), β-naphthol (1 mmol), and benzamide
(1.2 mmol) in the presence of TCCA was selected as a model reaction and the effects of
the reaction parameters such as amount of the catalyst and temperature were studied in de-
tail. The best result was obtained with 2.5 mol% of TCCA under solvent-free conditions at
100◦C. Several structurally diverse aldehydes (Table 1) were subjected to condensation with
β-naphthol and acetamide or benzamide under the catalytic influence of TCCA (2.5 mol%)
and solvent-free conventional heating, and 1-amidoalkyl-2-naphthol derivatives were ob-
tained in high yields. The tolerance of the present method toward various functionalities
present in the substrates, viz., halides, methoxy, and nitro groups, generalizes the scope of
the present method.
The practical synthetic efficiency of this reaction was highlighted by the reaction of
terephthaldehyde with β-naphthol and acetamide to give structurally complex amidoalkyl
naphthol derivative (4w or x) (Scheme 2, Table 3).
We note that the use of one equiv. of 2-naphthol, one equiv. of terephthaldehyde, and
1.2 equiv. of acetamide with TCCA (5 mol%) afforded only monomer 4x in 84% (Table 3,
Entry 5).
Synthetically, chemoselectivity in chemistry is regarded as one of the most important
aspects of organic reactions. In this regard, preparation of 1-amidoalkyl-2-naphthols in the
presence of NBPI as catalyst, bromination of the aromatic ring did not occur and only the
desired products were obtained (Scheme 3).53
It is presumed that the reaction proceeds via the formation of an orthoquinone me-
thide (o-QM) initiated by nucleophilic addition of 2-naphthol to the aldehyde activated by
coordination to the oxophilic sodium (or bromonium or chloronium) ion as illustrated in
Scheme 4.

256
Maleki and Taimazi
Me
HO
O
HN
OHC
CHO
OH
NH
O
OH
+
NaCl (0.07 g)
Me
Solvent-free/1100C
4w
Me
or
NBPI(10mol%) or TCCA (5 mol%)
Solvent-Free/1000C
O
HN
+
CHO
O
OH
NH2
Me
4x
Scheme 2
Ph
NHCOR1
CHO
OH
OH
NBPI
+
+ PhCONH2
Solvent-free/1000C
75 min
82 %
Scheme 3
X
H
H
Ar
H
OX
Ar
OX
OH
O
OH
OH
Ar
H
X = Cl or Br or Na
HOX
NHCOR1
OH
Ar
H
O
Ar
Ar
H
OX
X+
1RCONH2
[o-QM]
Scheme 4

Synthesis of 1-Amidoalkyl-2-naphthols
257
Table 3
Synthesis of bis(1-Amidoalkyl-2-naphthol) (4w) and Mono-substituted Compound(4x) in
the Presence of NaCl or NBPI (10 mol%) or TCCA (5 mol%)
mp (◦C)
Time
Entry Catalyst I/II/IIIa (min) Yield (%)
Found
Reported
1
2
3
4
5
6
NaCl
NaCl
NBPI
NBPI
TCCA
TCCA
1/1/1.2
1/2/2.4
1/1/1.2
1/2/2.4
1/1/1.2
1/2/2.4
40
40
40
50
35
60
22 (43)b 235–236 (279–281)c 237–240 (277–279)
52 (26)b 235–236 (279–281)c 237–240 (277–279)
16 (40)b 234–236 (279–281)c 237–240 (277–279)
32 (46)b 234–236 (279–281)c 237–240 (277–279)
84 (0)b
12 (79)b 234–237 (271–273)c 237–240 (277–279)
237–240
237–240
aMolar ratio of terephthaldehyde (I), β-naphthol (II), and acetamide (III).
bThe yield of bis(1-amidoalkyl-2-naphthol) (4w) is given in parentheses.
cMelting point of bis(1-amidoalkyl-2-naphthol) (4w) is given in parentheses.
In conclusion an efficient, simple, and safe procedure for the preparation of the 1-
amidoalkyl-2-naphthol derivatives was reported in this work. The notable advantages of this
methodology are operational simplicity, generality, non-hazardous experimental conditions,
short reaction times, and easy work-up.
Experimental Section
1
IR spectra were recorded on a Shimadzu 435-U-04 spectrophotometer (KBr pellets). H
and 13C NMR spectra were obtained using Bruker DRX-300 Advance spectrometer in
DMSO-d6 or CDCl3 using TMS as an internal reference. Melting points were determined
in open capillary tubes in a Stuart BI Branstead Electrothermal Cat No:IA9200 apparatus
and are uncorrected.
General Procedure for the Synthesis of 1-Amidoalkyl-2-naphthols
Derivatives
A mixture of aldehyde (1, 1 mmol), β-naphthol (2, 1 mmol), amide (acetamide or benzamide
(1.2 mmol), and NaCl (0.07 g) or NBPI (10 mol%) or TCCA (2.5 mol%) in absence of
solvent was stirred on an oil bath for a suitable time (see Tables 1 and 3). The reaction
was monitored by TLC. After completion, an appropriate amount (5 ml) of hot EtOH
(96%) was added and the mixture stirred for 10 min. Then, the catalyst was separated by
filtration and the filtrate was poured into crushed ice. The solid product, which separated was
collected and recrystallized from ethanol to give pure crystalline 1-amidoalkyl-2-naphthol
derivatives. Compounds were characterized by their melting points, which are given in
Table 1.

258
Maleki and Taimazi
Spectroscopic Data of Representative Compounds
α-(α-Acetamidobenzyl)-β-naphthol (4a), 1H NMR (300 MHz, DMSO-d6): δ 1.98 (s, 3H),
7.11–7.26 (m, 8H), 7.32–7.37 (m, 1H), 7.37–7.84 (m, 3H), 8.43 (d, 1H, NH, exchangeable
with D2O), 10.01 (s, 1H, OH); 13C NMR (75 MHz, DMSO-d6): δ 22.56, 47.81, 118.45,
118.84, 122.38, 123.32, 125.14, 126.05, 126.30, 127.00, 127.99, 128.45, 128.55, 128.91,
129.25, 129.56, 132.33, 142.62, 153.17, 169.26; IR: (KBr disc) cm−1: 3320, 3220–2846,
1640.
α-(α-Benzamidobenzyl)-β-naphthol (4m), 1H NMR (300 MHz, DMSO-d6): δ
7.17–7.31 (m, 8H), 7.42–7.56 (m, 4H), 7.77–7.86 (m, 4H), 8.05 (d, 1H), 9.00 (d, 1H,
NH, exchangeable with D2O), 10.31 (s, 1H, OH); 13C NMR (75 MHz, DMSO-d6): δ 49.45,
118.46, 118.79, 123.17, 126.69, 127.05, 127.39, 128.63, 128.70, 129.02, 129.85, 131.97,
132.56, 134.43, 142.15, 153.30, 166.22; IR: (KBr disc) cm−1: 3321, 3184–2763, 1680.
Acknowledgment
The authors are thankful to research council of Hakim Sabzevari University for financial
support.
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