Tetrakis(acetonitrile)copper(I) hexafluorophosphate-promoted efficient synthesis of amidoalkyl naphthols under solvent-free conditions

Article abstract of DOI:10.1080/00397911.2010.545497

An efficient and direct protocol for the preparation of amidoalkyl naphthols employing a multicomponent, one-pot condensation reaction of β-naphthol, aromatic aldehydes, and amides (acetamide, benzamide, and urea) in the presence of tetrakis(acetonitrile)

Full text of DOI:10.1080/00397911.2010.545497

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Tetrakis(acetonitrile)copper(I)
Hexafluorophosphate–Promoted Efficient
Synthesis of Amidoalkyl Naphthols Under
Solvent-Free Conditions
Ebrahim Soleimani a & Mohsen Zainali a
a Department of Chemistry, Razi University, Kermanshah, Iran
Accepted author version posted online: 07 Dec 2011.Version of
record first published: 26 Mar 2012.
To cite this article: Ebrahim Soleimani & Mohsen Zainali (2012): Tetrakis(acetonitrile)copper(I)
Hexafluorophosphate–Promoted Efficient Synthesis of Amidoalkyl Naphthols Under Solvent-Free
Conditions, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 42:13, 1885-1889
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Synthetic Communications1, 42: 1885–1889, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.545497
TETRAKIS(ACETONITRILE)COPPER(I)
HEXAFLUOROPHOSPHATE–PROMOTED EFFICIENT
SYNTHESIS OF AMIDOALKYL NAPHTHOLS UNDER
SOLVENT-FREE CONDITIONS
Ebrahim Soleimani and Mohsen Zainali
Department of Chemistry, Razi University, Kermanshah, Iran
GRAPHICAL ABSTRACT
Abstract An efficient and direct protocol for the preparation of amidoalkyl naphthols
employing a multicomponent, one-pot condensation reaction of b-naphthol, aromatic alde-
hydes, and amides (acetamide, benzamide, and urea) in the presence of tetrakis(acetonitri-
le)copper(I) hexafluorophosphate [Cu(CH3CN)4PF6] under solvent-free conditions at
80 ꢀC is described. Good yields, short reaction time, and easy workup are advantages of this
procedure.
Keywords Amidoalkyl naphthols; Cu(CH3CN)4PF6; multicomponent reaction; b-naph-
thol; solvent-free
INTRODUCTION
Multicomponent reactions (MCRs) have been frequently used by synthetic
chemists as a facile means to generate molecular diversity from bifunctional sub-
strates that react sequentially in an intramolecular fashion.[1] Devising types of
MCRs that achieve the formation of multiple bonds in a single operation is one
of the major challenges in modern organic synthesis.[2] As such processes avoid
time-consuming and costly purification processes, as well as protection–deprotection
steps, they are inherently more environmentally benign and atom economic.[3] They
provide a powerful tool for one-pot synthesis of diverse and complex compounds as
well as small and drug-like heterocycles.[4]
1-Amidoalkyl-2-naphthols are important intermediates that can be easily con-
verted into biologically active 1-aminoalkyl-2-naphthols derivatives by amide
hydrolysis.[5] The classical method for synthesis of 1-amidoalkyl-2-naphthols
Received November 23, 2010.
Address correspondence to E. Soleimani, Department of Chemistry, Razi University, Kermanshah
67149, Iran. E-mail: e_soleimanirazi@yahoo.com
1885

1886
E. SOLEIMANI AND M. ZAINALI
Scheme 1. Synthesis of amidoalkyl naphthols in the presence of Cu(CH3CN4)PF6 catalyst.
involves the condensation of aryl aldehydes, b-naphthol, and an amide in the presence
of Lewis or Brønsted acid catalysts such as such as para-toluene-sulfonic acid
(p-TSA),[6] montmorillonite K10,[7] Ce(SO4)2,[8] iodine,[9] Fe(HSO4)3,[10] Sr(OTf)2,[11]
K5CoW12O40 ꢁ 3H2O,[12] sulfamic acid,[13] molybdophosphoric acid,[14] cation-
exchange resins,[15] silica sulfuric acid,[16] indium(III) chloride,[17] and ionic liquid.[18]
However, some of the reported methods suffer from disadvantages such as prolonged
reaction time, poor yield of products, toxic and corrosive reagents, and the use of
additional microwave or ultrasonic irradiation.
In continuation of our work to develop new synthetic methodologies,[19] herein
we report a new, convenient, mild, and efficient procedure for one-pot,
three-component synthesis of amidoalkyl naphthol derivatives 4 from various aryl
aldehydes 1, b-naphthol 2, and different amides 3 (acetamide, benzamide, and urea)
in the presence of Cu(CH3CN)4PF6 as an effective catalyst under solvent-free
conditions at 80 ꢀC (Scheme 1).
Cu(CH3CN)4PF6 is a free-flowing, white, microcrystalline powder that does
not darken on long-term storage in an inert atmosphere. Exposure to air for longer
than about 1 h results in minor surface oxidation as a result of the slightly hygro-
scopic nature of the complex. The complex is moderately soluble in polar solvents
and is remarkably stable to air oxidation in CH3CN solution.[20]
RESULTS AND DISCUSSION
To study the feasibility of the Cu(CH3CN)4PF6 catalysis in this reaction, the
reaction of benzaldehyde, b-naphthol, and acetamide was selected as a model under
solvent-free conditions.
We first studied the model reaction catalyzed by Cu(CH3CN)4PF6 (10 mol%) at
different temperatures. The reaction rate was increased as the reaction temperature
was raised. When it was carried out at 80 ꢀC, the maximum yield was obtained in a
short reaction period. Next, to evaluate the effect of catalyst concentration, the
model reaction was carried out in the presence of different amounts of catalyst (5,
10, 15, 20 and 25 mol%) at 80 ꢀC. The result showed that 10 mol% of catalyst was
sufficient to achieve a fairly good yield. The results of using Cu(CH3CN)4PF6 as a
catalyst in the reaction of various aldehydes, b-naphthol, and various amides are
summarized in Table 1. Various functionalities present in the aryl aldehydes such
as halogen, hydroxy, methyl, and nitro groups in amides such as acetamide, benza-
mide, and urea were tolerated. In all these cases, the corresponding amidoalkyl
naphthols were obtained in good yields.
To show the merit of the present work in comparison with reported results in
the literature, we compared results of Cu(CH3CN)4PF6 with p-TSA,[6] Ce(SO4)2,[8]

SYNTHESIS OF AMIDOALKYL NAPHTHOLS
1887
Table 1. Preparation of 1-amidoalkyl-2-naphthols
Mp (ꢀC)
Entry
R1
R2
Time (min)
Yield (%)
Found
Reported
1
2
H
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
NH2
NH2
NH2
C6H5
C6H5
60
45
35
20
65
70
80
35
70
15
27
30
56
50
93
94
90
98
75
78
75
80
97
75
89
90
77
75
238–240
246–248
238–240
236–238
205–207
218–221
212–214
197–200
221–223
169–172
180–182
162–164
175–177
214–216
241–243[8]
248–250[10]
241–242[10]
—
4-NO2
3-NO2
3-OH
4-OH
4-Cl
3
4
5
—
6
223–225[8]
213–215[15]
198–199[8]
222–223[10]
172–174[12]
184–186[12]
168–169[12]
177–178[12]
216–217[12]
7
2-Cl
8
2,4-Cl
4-CH3
H
9
10
11
12
13
14
3-NO2
4-Cl
4-Cl
3-NO2
iodine,[9] and K5CoW12O40 ꢁ 3H2O[12] in the synthesis N-[(3-nitro phenyl)-(2-
hydroxy-naphthalen-1-yl)-methyl]-acetamide from 3-nitro benzaldehyde, acetamide,
and 2-naphthol. As shown in Table 2, Cu(CH3CN)4PF6 can act as effective catalyst
with respect to reaction times, yields, and simplified conditions.
CONCLUSION
In conclusion, we have developed a simple and efficient synthesis of amidoalkyl
naphthols using Cu(CH3CN)4PF6 catalyst under solvent-free conditions. This
method offers some advantages in terms of simplicity of performance, short reaction
times, good yields, and solvent-free condition, and it follows the line of green chem-
istry. This protocol could serve as a valuable alternative to known reaction systems.
EXPERIMENTAL
Cu(CH3CN)4PF6 (0.037 g, 0.1 mmol) was added to a mixture of 2-naphthol
(1 mmol), aldehydes (1 mmol), and acetamide (1.2 mmol). The mixture was stirred
at 80 ꢀC in an oil bath and the reaction was followed by thin-layer chromatography
(TLC). After completion, the mixture was cooled to 25 ꢀC, dichloromethane was
Table 2. Comparison of the efficiencies of various catalysts used in the synthesis of amidoalkyl naphthols
Catalyst
Conditions=Temp. (ꢀC)
Time
Yield (%)
Reference
p-TSA
Ce(SO4)2
Solvent-free=125
Under reflux
5 h
16 h
5 h
88
65
81
78
90
6
8
I2
Solvent-free=125
Solvent-free=120
Solvent-free=80
9
12
K5CoW12O40 ꢁ 3H2O
Cu(CH3CN)4PF6
3 h
35 min
This work

1888
E. SOLEIMANI AND M. ZAINALI
added, and the mixture stirred for 5 min. Products were filtered and recrystallized
from aqueous ethanol.
All the products (except entries 4 and 5) are known compounds, which were
1
characterized by IR and H NMR spectral data, and their melting points were
compared with literature reports.
N-((2-Hydroxynaphthalen-1-yl)(3-hydroxyphenyl)methyl)acetamide
(Entry 4)
White powder (0.30 g, yield 98%); mp 236–238 ꢀC. IR (KBr) (nmax=cmꢂ1):
3456, 1612, 1539, 1443. MS, m=z (%): 307 (Mþ, 20), 247 (50), 230 (100), 115 (20).
1H NMR (200 MHz, DMSO-d6): dH (ppm) ¼ 1.98 (3H, s, CH3), 6.57–7.83 (11H,
3
m, H-Ar and CH-NH), 8.41 (1H, d, JHH ¼ 8.3 Hz, H-Ar), 9.22, 10.00 (2H, 2 s,
2OH). 13C NMR (50 MHz, DMSO-d6): dC (ppm) ¼ 22.35 (CH3), 47.35 (CH-NH),
112.80, 116.43, 118.14, 118.60, 122.09, 123.08, 125.96, 128.20, 128.63, 128.84,
=
132.08, 143.85, 152.81, 156.83 (C-Ar), 168.91 (C O). Anal. calcd. for C19H17NO3:
C, 74.25; H, 5.58; N, 4.56. Found: C, 74.30; H, 5.55; N, 4.63.
N-((2-Hydroxynaphthalen-1-yl)(4-hydroxyphenyl)methyl)acetamide
(Entry 5)
White powder (0.23 g, yield 75%); mp 205–207 ꢀC. IR (KBr) (nmax =cmꢂ1):
3408, 1609, 1510, 1430. MS, m=z (%): 307 (Mþ, 20), 247 (50), 230 (100), 202 (15),
115 (20). 1H NMR (200 MHz, DMSO-d6): dH (ppm) ¼ 1.93 (3H, s, CH3),
6.61–8.37 (12H, m, H-Ar and CH-NH), 9.18, 9.93 (2H, 2 s, 2OH). 13C NMR
(50 MHz, DMSO-d6): dC (ppm) ¼ 22.41 (CH3), 47.17 (CH-NH), 114.46, 118.19,
118.78, 122.03, 123.00, 125.88, 126.97, 128.18, 128.68, 131.99, 132.22, 152.69,
=
155.37 (C-Ar), 169.00 (C O). Anal. calcd. for C19H17NO3: C, 74.25; H, 5.58; N,
4.56. Found: C, 74.30; H, 5.55; N, 4.63.
ACKNOWLEDGMENT
We gratefully acknowledge financial support from the Research Council of
Razi University.
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