One-pot solvent-free sonochemical synthesis of 1-amidoalkyl-2-naphthols

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Organic Preparations and Procedures
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One-pot Solvent-free Sonochemical
Synthesis of 1-Amidoalkyl-2-naphthols
Saurabh Puri a , Balbir Kaur a , Anupama Parmar b & Harish Kumar c
a Department of Chemistry , Punjabi University , Patiala-147002
(Pb.) , INDIA
b Post Graduate Dept. of Chemistry , M.M. Modi College Patiala
c Department of Chemistry , Sant Longowal Institute of Engineering
& Technology , Longowal-148106 (Pb.) , INDIA
Published online: 19 Jan 2012.
To cite this article: Saurabh Puri , Balbir Kaur , Anupama Parmar & Harish Kumar (2012) One-
pot Solvent-free Sonochemical Synthesis of 1-Amidoalkyl-2-naphthols, Organic Preparations
and Procedures International: The New Journal for Organic Synthesis, 44:1, 91-95, DOI:
10.1080/00304948.2012.643200
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Organic Preparations and Procedures International, 44:91–95, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5452 online
DOI: 10.1080/00304948.2012.643200
One-pot Solvent-free Sonochemical Synthesis
of 1-Amidoalkyl-2-naphthols
Saurabh Puri,1 Balbir Kaur,1 Anupama Parmar,2 and Harish Kumar3
1Department of Chemistry, Punjabi University, Patiala-147002 (Pb.), INDIA
2Post Graduate Dept. of Chemistry, M.M. Modi College Patiala
3Department of Chemistry, Sant Longowal Institute of Engineering
& Technology, Longowal-148106 (Pb.), INDIA
In recent years, organic synthesis involving greener processes, including solvent-free con-
ditions, has been explored due to stringent environmental and economic regulations.1
Homogeneous, liquid acid catalysts, such as H2SO4, HCl and complexes of BF3 are inher-
ently associated with problems such as high toxicity, corrosion, catalyst waste, difficulty
in separation and recovery. Replacement of these conventional acids by solid catalysts is
desirable to achieve effective catalyst handling and product purification.
Multicomponent reactions (MCRs) have elicited increased interest since they are per-
formed without the need to isolate any intermediate, thus reducing time and saving energy
and raw materials.2 One of these MCRs is the synthesis of amidoalkyl naphthols, which
are ubiquitous to a variety of biologically important natural products and potent drugs,
including a number of nucleoside antibiotics and HIV protease inhibitor, such as ritonavir
and lipinavir.3,4 Furthermore, amidoalkyl naphathols can be converted to useful synthetic
building blocks for drugs exhibiting depressor and bradycardiac activities.5,6 The prepa-
ration of amidoalkyl naphthols (1) can be carried out by the condensation of aromatic
aldehydes, 2-naphthol and urea or amides in the presence of Lewis or Brønsted acid cat-
alysts such as montmorillonite K10 clay,7 HClO4-SiO2,8 iodine,9 K5CoW12O40.3H2O,10
p-TSA,11 sulfamic acid,12 cation-exchange resins13 and ionic liquids.14,15 One of the major
drawbacks of these reactions is that in some cases when a solid aldehyde or high amounts of
catalyst is used, an organic solvent such as dichloroethane is needed. Many of the reported
methods suffer from long reaction times, poor yields, and harsh reaction conditions. These
shortcomings suggest that a safe, eco–friendly and efficient method be devised.
Ultrasound-assisted organic synthesis (UAOS) is a powerful and green approach16,17
which is increasingly used to accelerate the rates and improve the yields of reactions.18–23
In continuation of our work on the study of new catalysts24–27 for organic functional group
transformations, we now report a general, efficient and eco-friendly solvent-free procedure
Received May 20, 2011; in final form October 5, 2011.
Address correspondence to Harish Kumar, Department of Chemistry, Sant Longowal Institute
of Engineering & Technology, Longowal-148106 (Pb.), India. E-mail: hk67@rediffmail.com
91

92
Kumar et al.
Ar
NHCOR
OH
OH
+ Ar-CHO +
Cu(ClO4)2.6H2O
))))
R-CONH
2
(1a-l)
b) R = CH3 , Ar = 3-NO2C6H4 c) R = CH3 , Ar = 4-FC6H4
a) R = CH3 , Ar = C6H5
d) R = CH3 , Ar = 4-ClC6H4
g) R = NH2 , Ar = C6H5
e) R = CH3 , Ar = 3-BrC6H4
h) R = NH2 , Ar = 3-NO2C6H4
k) R = C6H5 , Ar = 4-ClC6H4
f) R = CH3 , Ar = 2-NO2C6H4
i) R = NH2 , Ar = 4-ClC6H4
l) R = C6H5 , Ar = C6H5
j) R = C6H5 , Ar = 4-FC6H4
Scheme 1
for the synthesis of 1-amidoalkyl-2-naphthols (1a-l) by condensation of 2-naphthol,
urea/amides and aromatic aldehydes catalyzed by 20 mole% of copper perchlorate hexahy-
drate at 35 kHz under ultrasonic irradiation (Scheme 1).
In initial experimentations to determine the optimum amount of catalyst, 2-naphthol
was first treated with benzaldehyde and urea for 30 minutes under ultrasound irradiation in
presence of varying mol% of copper perchlorate hexahydrate. The best results were obtained
using 20 mol% of catalyst. Using lower amounts of catalyst resulted in lower yields, while
higher amounts of catalyst did not affect reaction time and yield. In absence of the catalyst,
the yield was very low. To verify the effect of ultrasound irradiation, the synthesis of 1g
was performed with and without ultrasound irradiation; in this case, the use of ultrasound
irradiation led to a faster reaction and higher yield. However, in terms of the scope of
the reaction, yields were very poor with aliphatic aldehydes, phenols and 1-naphthols.
Only 2-naphthol was used as reactant as 1-amidoalkyl-2-naphthols can be converted to
important drug like 1-aminomethyl-2-naphthols derivatives by amide hydrolysis reaction.
Unlike previously reported methods, the present procedure does not require toxic organic
solvents. A wide range of aromatic aldehydes were used and gave excellent yields of 1-
amidoalkyl-2-naphthols. All the products were characterized by elemental analysis, NMR
and by comparison of melting points with authentic samples (Table 1).
Experimental Section
1
All mps are uncorrected and were determined in open capillaries. H NMR spectra were
measured on a AL-300F (Bruker) FT NMR spectrophotometer using tetramethylsilane
(TMS) as internal standard. Sonication was performed using an ELMA Transsonic T
310/H Ultrasonic cleaner with a frequency of 35 KHz (Hans Schmidbauer GmbH &
Co., Germany). Copper perchlorate hexahydrate was prepared by a standard procedure28
and perchlorates are safe and stable under ordinary conditions of use and storage, but
their contact with heat and reducing agents must be avoided as Lithium and magnesium
perchlorates are dangerous if heated over their decomposition temperatures (300–500◦C).29

Sonochemical Synthesis of 1-Amidoalkyl-2-Naphthols
93
Table 1
Yields, mps and 1H NMR Spectral Data of 1a-l
Cmpd Yield mp.(◦C)
Time
(lit. mp.) (min.)
1H NMRa (δ)
(%)
1a
1b
90
229–231
30 9.98 (1H, s, OH), 8.44 (1H, d, J = 8.4 Hz, NH), 7.84–
7.75 (3H, m, ArH), 7.36 (1H, t, J = 7.6 Hz, ArH),
7.27–7.20 (4H, m, ArH), 7.17–7.12 (4H, m, ArH),
1.98 (3H, s, CH3)
80 10.13 (1H, s, OH), 8.63 (1H, d, J = 8.0 Hz, NH),
8.06–8.01 (2H, m, ArH), 7.88–7.80 (3H, m, ArH),
7.59–7.53 (2H, m, ArH), 7.42 (1H, t, J = 7.6 Hz,
ArH), 7.30 (1H, t, J = 7.6 Hz, ArH), 7.23–7.17 (2H,
m, ArH), 2.02 (3H, s, CH3).
(229–230)12
88
236–238
(236–237) 12
1c
1d
1e
86
89
90
203–204
30 9.62 (1H, s), 8.05 (1H, d, j = 6Hz), 7.77–7.41 (3H, m),
(203–205) 12
233–234
7.32–6.86 (7H,m), 2.07 (3H, s).
75 9.68 (1H, brs), 8.12–7.98 (2H, m), 7.78–7.59 (2H, m),
7.30 (1H, m), 7.28–7.06 (7H, m), 2.02 (3H, s).
60 1.97 (s, 3H), 7.08 (d, J = 7.2 Hz, 1H), 7.19 (t, J =
7.2 Hz, 2H), 7.26 (t, J = 7.6 Hz, 1H), 7.31–7.40 (m,
4H), 7.76–7.81 (m, 3H), 8.59 (d, J = 8.4 Hz, 1H),
10.00 (s, 1H).
(232–233) 12
245–247
(250–252)30
1f
88
211–213
(210–212)30
75 10.02 (1H, s, OH), 8.51 (1H, d, J = 8.0 Hz, NH),
8.10–8.00 (2H, m, ArH), 7.80–7.74 (2H, m, ArH),
7.59–7.53 (3H, m, ArH), 7.30–7.15 (3H, t, ArH),
2.02 (3H, s, CH3)
1g
1h
1i
90
85
90
173–174
35 9.97 (1H, s, OH), 7.83–7.75 (3H, m, ArH), 7.40 (1H, s,
NH), 7.29–7.11 (7H, m, ArH), 6.94 (2H, s), 5.86
(2H, s, NH2).
40 10.13 (1H, s, OH), 8.09–7.99 (2H, m), 7.87–7.46 (7H,
m), 7.33–7.21 (2H, m), 7.12 (1H, d, J = 8.4 Hz),
7.06–6.99 (1H, m), 5.96 (1H, s).
60 10.00 (1H, s, OH), 7.83–7.76 (3H, m, ArH), 7.43 (1H,
s, NH), 7.31–7.14 (6H, m, ArH), 6.90 (2H, s), 5.86
(2H, s, NH2).
(172–174)12
184–185
(184–186)12
169–170
(168–169)12
1j
86
84
198–199
55 10.37(1H, s, OH), 9.35 (1H, d, J = 9 Hz, NH),
(193–194)12
178–180
8.08-7.06 (16H, m, ArH).
1k
75 10.36 (1H, s, OH), 9.02 (1H, d, J = 8.5 Hz, NH), 8.06
(1H, d, J = 8.5 Hz, ArH), 7.88–7.80 (4H, m, ArH),
7.57–7.45 (4H, m, ArH), 7.35–7.23 (7H, m, ArH).
45 10.34 (1H, s, OH), 9.03 (1H, d, J = 8.4 Hz, NH), 8.09
(1H, d, J = 8.8 Hz, ArH), 7.88–7.79 (4H, m, ArH),
7.57–7.45 (4H, m, ArH), 7.33–7.19 (8H, m, ArH).
(177–178)12
1l
89
235–236
(234–236)12
a) in DMSO –d6.

94
Kumar et al.
Typical Procedure
To a mixture of 2-naphthol (0.144 g; 1 mmol), benzaldehyde (0.106 g; 1 mmol) and urea
(0.066 g; 1.1 mmol) was added copper perchlorate hexahydrate (0.287 g; 20 mol%) in a
50 mL beaker and the reaction mixture was subjected to ultrasound irradiation at room
temperature for 30–80 min. The progress of reaction was followed by TLC (silica gel using
methanol: chloroform (1 : 9) as solvent). After completion of the reaction, the reaction
mixture was quenched by addition of water (15–20 mL) and stirred for 5 min to dissolve
the copper perchlorate. The insoluble solid was collected and recrystallized from ethanol
to afford the pure product (1a-l).
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