Aerial oxidation of bisnaphthols to spironaphthalenones by a recyclable magnetic core-sell nanoparticle-supported TEMPO catalyst

Article abstract of DOI:10.1016/j.crci.2013.02.002

Aerial oxidative cyclization of bisnaphthols to their corresponding mixture of two isomeric spirans 3 and 4 has been carried out using a catalytic amount of magnetic core-shell nanoparticle-supported TEMPO (MNST) combined with a small amount of FeCl₃·6H₂O. This catalytic system consistently has the advantages of moderate to good yields, low reaction times, mild and convenient conditions, simple experimental and work-up procedure, and of being environmentally benign and highly economic. The magnetically separable MNST catalyst makes it possible for it to be recovered and recycled for several times without significant loss of activity.

Full text of DOI:10.1016/j.crci.2013.02.002

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Preliminary communication/Communication
Aerial oxidation of bisnaphthols to spironaphthalenones by a recyclable
magnetic core-sell nanoparticle-supported TEMPO catalyst
*
Ahmad Khorramabadi-zad , Saba Daliran, Ali Reza Oveisi
Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Aerial oxidative cyclization of bisnaphthols to their corresponding mixture of two isomeric
spirans 3 and 4 has been carried out using a catalytic amount of magnetic core-shell
nanoparticle-supported TEMPO (MNST) combined with a small amount of FeCl3ꢀ6H2O.
This catalytic system consistently has the advantages of moderate to good yields, low
reaction times, mild and convenient conditions, simple experimental and work-up
procedure, and of being environmentally benign and highly economic. The magnetically
separable MNST catalyst makes it possible for it to be recovered and recycled for several
times without significant loss of activity.
Received 16 November 2012
Accepted after revision 4 February 2013
Available online xxx
Keywords:
Bisnaphthols
Aerial oxidative cyclization
Spirodienones
ß 2013 Published by Elsevier Masson SAS on behalf of Acade´mie des sciences.
Magnetically separable TEMPO
Iron chloride
1. Introduction
For example, hexacyanoferrate (in benzene and pyridine)
[7], 2,4-di-t-butyl-6-phenylphenoxyl [8], 2,3-dichloro-5,6-
Oxidation of bis(2-hydroxy-1-naphthyl)methanes as a
subunit of calix[n]arenes (i) has been used for the
preparation of spirodienones [1] (ii), which is an important
reaction in the biosynthesis of certain plant products
(Fig. 1) [2–4].
Abel, in 1892, reported the oxidation of bisnaphthols to
spirodienones with Br2 in alkaline solution [3]. The product
was believed to be a peroxide, but on the basis of chemical
evidence its structure was assigned as spirodienone [4,5].
Kasturi et al. perfectly studied the chemistry of spirodie-
none family [6]. According to Kasturi’s reports, Abel’s
ketone derivatives have two sets of diastereomers which
are assigned by the fact that one diastereomer, 3, shows in
dicyano-1,4-benzoquinone (DDQ) [9] and hydrogen per-
oxide/MoO3 [10] give a mixture of two isomeric spiro
products. Trichloroisocyanuric acid (TCCA) [11], potassium
hypobromite and persulphate give 3 [7], whereas aerial
oxidation in the presence of Ph3Bi [12], periodic acid or its
sodium salt, and (diacetoxyiodo)benzene in benzene is
specific for 4 [8].
Most of these procedures have certain limitations, such
as tedious procedure, long reaction time, harsh reaction
conditions, poor yields and the use of toxic or expensive
reagents (Fig. 2). In continuation of our research area for
the oxidation of bisnaphthols [11,12], we were interested
in the use of TEMPO as a catalyst. Based on literature
survey and our previous experience, it was concluded that
a suitable candidate might be 2,2,6,6-tetramethylpiper-
idine-1-oxyl (TEMPO) [a stable free nitroxyl radical], which
has been used in many areas of synthetic organic
chemistry as a safe, weakly toxic and highly efficient
catalyst with the possible achievement of chemoselectivity
in the oxidation processes [13–20]. TEMPO is quite an
expensive reagent from which the separation of oxidation
products requires lengthy work-up procedures. In order to
fulfill the recovery problem, TEMPO has been immobilized
its 1HNM-R spectrum a doublet near
3’); while for the other one, 4, this hydrogen appears at
about 5.4 ppm, the up-field shift being due to the
shielding effect of the -phenyl ring (Fig. 2) [7]. It has
d6.1 ppm (vinylic H-
d
m
been reported that different oxidants give either one
isomer (3 or 4) or a mixture of the two isomeric products.
* Corresponding author.
E-mail address: khoram@gmail.com (A. Khorramabadi-zad).
1631-0748/$ – see front matter ß 2013 Published by Elsevier Masson SAS on behalf of Acade´mie des sciences.
http://dx.doi.org/10.1016/j.crci.2013.02.002
Please cite this article in press as: Khorramabadi-zad A, et al. Aerial oxidation of bisnaphthols to spironaphthalenones
by a recyclable magnetic core-sell nanoparticle-supported TEMPO catalyst. C. R. Chimie (2013), http://dx.doi.org/
10.1016/j.crci.2013.02.002

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Fig. 1. Calix[n]arenes (i) and spirodienones (ii).
that iron is an abundant inexpensive and environmentally
friendly metal, iron chloride has attracted a great deal of
attention in modern chemistry [23–25]. With the above
consideration and the need for new and green procedures
with minimum wastes,
a key challenge for today’s
environment, we now report the aerial oxidative cycliza-
tion of bisnaphthols using MNST in the presence of
FeCl3ꢀ6H2O (Scheme 1).
Fig. 2. Abel’s ketone derivatives (3 and 4).
2. Results and discussion
At the outset, to optimize the reaction conditions, the
aerial oxidation of bisnaphthol 1 was run using MNST in
the presence of different transition metal salts, such as Fe
(III), Mn (II), Cu (II), Co (II) as well as Nano–Fe3O4 as a co-
catalyst in acetonitrile at 40 8C, with bubbling air into the
reaction vessel (Table 1). As is clear from this Table, the
best results were obtained with FeCl3ꢀ6H2O as a co-catalyst
(Table 1, Entries 6-8). The amount of FeCl3ꢀ6H2O was
optimized at 1 mol% in order to reduce the reaction time
and to increase the product yield (Table 1, Entry 6).
Control tests in various solvents, such as acetonitrile,
ethanol, acetone, dichloromethane and water showed that
acetonitrile would be the best choice for the reaction to
proceed. An additional experiment was also performed for
three runs to test the reusability of the catalyst, using
oxidation of bisnaphthol 1 as a model reaction. After each
run, the catalyst was washed twice (2 ꢁ 10 ml) with hot
ethanol and dried. The reused catalyst was found to be
on either inorganic or organic supports such as silica [15],
organic polymers [16], mesoporous silica [17], function-
alized ionic liquids [18], and perfluoroalkyl systems with
multiple triazole moieties [19].
Recently, a good strategy has been proposed by Karimi
et al. for the aerial oxidation of alcohols using magnetic
core-shell nanoparticle-supported TEMPO as
a high
activity catalyst, which is easily separated with an external
magnetic field [20]. In addition, much attention has been
paid to the use of molecular oxygen or air as a highly green
oxidant [14,21,22]. Moreover, taking into account the fact
Table 1
Aerial oxidation of bisnaphthol 1 in the presence of different co-catalysts.
Entry
Co-catalyst (mol%)
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
CuCl2ꢀ4H2O (1)
Mn(OAc)2ꢀ4H2O (1)
Co(OAc)2ꢀ4H2O (1)
M*(acac)2 (1)
10
7
Trace
Trace
Trace
25
10
8
Nano–Fe3O4 (1)
FeCl3ꢀ6H2O (1)
FeCl3ꢀ6H2O (3)
FeCl3ꢀ6H2O (0.3)
10
3
–
80
15
8
60
45
M*: Co, Mn, Fe, Cu.
a
Separated yields; Reaction conditions: bisnaphthol 1 (1 mmol), MNST
(0.005 g, 0.001 mmol with respect to the TEMPO), co-catalyst, acetonitrile
(20–25 ml), 40 8C, bubbling air.
Scheme 1. Oxidation of bisnaphthols.
Please cite this article in press as: Khorramabadi-zad A, et al. Aerial oxidation of bisnaphthols to spironaphthalenones
by a recyclable magnetic core-sell nanoparticle-supported TEMPO catalyst. C. R. Chimie (2013), http://dx.doi.org/
10.1016/j.crci.2013.02.002

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3
Table 2
Aerial oxidation of bisnaphthols using MNST.
Entry
X
Product
Time (h)
Yield (%)a
Melting point (8C)
Diast.b (%)
Found
Lit [10–12]
3
4
3
4
3
4
1
2
3
4
5
6
7
8
9
10
H
2
4
4
3
4
5
3
3
5
5
4
80, 76c 76d
171–172
170–171
–
–
C6H5
3a, 4a
3b, 4b
3c, 4c
3d, 4d
3e, 4e
3f, 4f
3g, 4g
3h, 4h
3i, 4i
75
68
70
73
82
78
78
75
73
210–211
264–265
198–199
208–209
200–202
214–216
219–221
187–189
228–231
265–266
262–263
228–210
195–197
219–221
145–146
147–149
225–227
194–196
210–211
262–263
198–200
204–206
199–200
214–215
218–223
187–188
229–2230
263–264
262–263
227–229
195–197
217–220
145–146
146–148
225–227
194–196
85
20
50
55
75
55
50
70
60
15
80
50
45
25
45
50
30
40
4-ClC6H4
4-CH3C6H4
2,4-Cl2C6H3
4-CH3OC6H4
4-FC6H4
2-BrC6H4
3-CH3C6H4
2-CH3OC6H4
Reaction conditions: Bisnaphthol (1 mmol), MNST (0.005 g, 0.001 mmol with respect to the TEMPO), FeCl3ꢀ6H2O (1 mol%), acetonitrile (20–25 mL), 40 8C,
bubbling air.
a
Total yield (isomer 3 + isomer 4).
b
Diastereomeric ratio. The ratio of the two diastereomers, 3 and isomer 4, was determined by 1H-NMR.
c
Reuse of MNST in second run.
d
Reuse of MNST in third run.
R
R
OH
OH
X
N
O
N
O
Fe(III)
Complex
Fe(III)-MNST
R
R
(III)
Fe
H
O
N
O
Fe(III)
Fe(II)
1/4 O2
X
N
OH
O
H
R
A
1/2 H2O
R
N
O
(III)
Fe
H
O
N
HO
X
O
B
R
R
O
O
X
X
O
O
N
OH
N
O
C
1/4 O2
1/2 H2O
O
O
R
O
X
Si
NH
O
O
Fe O
3
4
R:
MNSTH:
X: H, Aryl
N
OH
R
Product
(two diastereomers)
MNST:
N
O
Scheme 2. A plausible mechanism for the aerial oxidation of bisnaphthols.
Please cite this article in press as: Khorramabadi-zad A, et al. Aerial oxidation of bisnaphthols to spironaphthalenones
by a recyclable magnetic core-sell nanoparticle-supported TEMPO catalyst. C. R. Chimie (2013), http://dx.doi.org/
10.1016/j.crci.2013.02.002

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Table 3
efficient, without significant loss in product yield (Table 2,
Entry 1). It should be noted that the co-presence of MNST
and FeCl3 was found to be necessary for the aerial
oxidation of bisnaphthols to occur (Scheme 1, Table 2).
As shown in Table 2, the aerial oxidative cyclization of
bisnaphthol derivatives works well with a variety of
substituted phenyl moieties bearing both electron-with-
drawing and electron-donating groups, such as OMe, Me, F,
Cl and Br. In all the cases, with the exception of bisnaphthol
1, it was noticed that the oxidation reaction led to the
synthesis of two sets of diastereomers, 3 and 4 (Table 2,
Entry 1–10). As it was mentioned earlier, the distinctive
feature of the two diastereomers is the different chemical
shifts of the corresponding vinylic hydrogens (H-3’).
Therefore, their percentage was obtained from the integral
ratio of H3’ hydrogens. As it has been stated by Dean and co-
workers, the diastereomeric ratio 3:4 is nearly independent
of the nature of the substituents on X [8]. In addition, as
reported in the literature, the colour of 3 is bright yellow,
while 4 is cream or faintly yellow in colour [8].
A mechanistic rationalization for the aerial oxidation of
bisnaphthols is shown in Scheme 2. As reported in
literature [11,12,14,23,26,27], at the first step, Fe (III)
and MNST give active Fe (III)–MNST complexes. The next
step is the coordination of bisnaphthol to Fe (III)–MNST
complex to produce intermediate A. Abstraction of the
hydrogen of O–H by MNST then results in a radical
intermediate B, which affords diradical species C, MNSTH
and Fe (II) species after intramolecular one-electron
transfer reaction. Finally, diradical species C leads to the
formation of spiro products. The resulting Fe (II) species
will then react with MNST via another one-electron
transfer to give Fe (III). MNSTH is finally oxidized by
molecular oxygen to MNST and water.
Rf values of products.
Entry
X
Producta
Rf
3
4
1
2
3
4
5
6
7
8
9
10
H
2
0.55
C6H5
3a, 4a
3b, 4b
3c, 4c
3d, 4d
3e, 4e
3f, 4f
3g, 4g
3h, 4h
3i, 4i
0.68
0.54
0.74
0.48
0.77
0.58
0.71
0.62
0.71
0.58
0.42
0.65
0.37
0.67
0.42
0.54
0.55
0.61
4-ClC6H4
4-CH3C6H4
2,4-Cl2C6H3
4-CH3OC6H4
4-FC6H4
2-BrC6H4
3-CH3C6H4
2-CH3OC6H4
a
In each case, the two isomers 3 and 4 could be separated by column
chromatography (ethyl acetate:n-hexane, 2:10).
Melting points were determined on a Stuart Scientific
SMP3 apparatus and are uncorrected. Chromatographic
separations were performed on silica gel 60 (230–400
mesh). The desired pure products were identified by
comparison of their physical and spectroscopic data with
those of known compounds [10–12].
4.2. A typical procedure for the oxidation of bisnaphthols
Into
a round bottom flask (50 ml), a mixture of
bisnaphthol (1 mmol), FeCl3ꢀ6H2O (0.01 mmol) and MNST
(0.005 g) was poured in acetonitrile (20–25 ml). Into the
resulting mixture air was bubbled at 40 8C (for the
indicated time in Table 2). The progress of the reaction
was followed by TLC. After completion of the reaction, the
catalyst (MNST) was separated by an external magnet, the
excess solvent concentrated by evaporation and the crude
mixture was purified by column chromatography (ethyl
acetate:n-hexane, 2:10) to obtain the pure product. The Rf
values were also determined using the ratio of ethyl
acetate to hexane (see Table 3). All of the desired products
were characterized by comparison of their physical and
1H-NMR data with those of known compounds [10–12].
3. Conclusions
In conclusion, we have developed the oxidation of
bisnaphthols to their corresponding spirans (a mixture of
two diastereomers, 3 and 4) in the presence of MNST/
FeCl3ꢀ6H2O/O2 as a highly efficient and environmentally
friendly catalyst. This work consistently has several
advantages, such as using magnetically separable TEMPO
catalyst, the reusability of MNST, small amounts of
FeCl3ꢀ6H2O as an inexpensive co-catalyst, air as a green
oxidant, fairly short reaction times, moderate to good
yields, mild reaction conditions, highly economic and
simple experimental procedure.
4.2.1. Spiro{naphthalene-1(2H),20(10H)-naphtho[2,1-
b]furan}-2-one (2)
Yellow solid, yield 80%; IR (
1H-NMR (90 MHz, CDCl3):
3.50 and 4.1 (2H, dd, J = 16 Hz
due to hydrogens number 1); 6.30 (1H, J = 9.9 Hz due to
6.90–7.99 (11H, Ar and hydrogen
n
max, cmꢂ1): 1685 (C5O).
d
d
hydrogen number 30);
number 40).
d
4.2.2. 10-Phenyl-spiro{naphthalene-1(2H),20(10H)-
4. Experimental
naphtho[2,1-b]furan}-2-one (3a and 4a)
Yellow solid, yield 75%; IR (
NMR (90 MHz, CDCl3): 5.21 and 5.40 (2H, s, hydrogen
number 1); 5.53 and 6.28 (1H, J = 10 Hz and J = 9.9 Hz due
n
max, cmꢂ1): 1687 (C5O). 1H
4.1. General procedures and materials
d
d
All solvents and reagents were obtained from Merck
and used without further purification. Arylbisnaphthols
(Hewitt’s method) [8,28,29], methylenbisnaphthol (Mir-
onove’s method) [30] and magnetic core-shell nanoparti-
cle-supported TEMPO (MNST) [20] were prepared
according to the reported procedures. The NMR spectra
were run on Jeol 90 MHz and Bruker 500 MHz instruments.
to hydrogen number 30);
hydrogen number 40).
d6.95–7.99 (11H, Ar and
4.2.3. 10-(4-Chlorophenyl)-spiro{naphthalene-1(2H),20(10H)-
naphtho[2,1-b]furan}-2-one (3b and 4b)
Yellow solid, yield 68%; IR (
1H-NMR (90 MHz, CDCl3):
5.17 and 5.36 (1H, s, hydrogen
n
max, cmꢂ1): 1678 (C5O).
d
Please cite this article in press as: Khorramabadi-zad A, et al. Aerial oxidation of bisnaphthols to spironaphthalenones
by a recyclable magnetic core-sell nanoparticle-supported TEMPO catalyst. C. R. Chimie (2013), http://dx.doi.org/
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5
number 1);
d
5.58 and 6.27 (1H, d, J = 9.8 Hz and J = 10 Hz
4.2.10. 10-(2-Methoxyphenyl)-spiro{naphthalene-
1(2H),20(10H)-naphtho[2,1-b]furan}-2-one (3i and 4i)
Yellow solid, yield 73%; IR (
max, cmꢂ1): 1681(C5O).
1H-NMR (90 MHz, CDCl3):
3.55 and 3.66 (3H, s); 5.44
and 5.55 (1H, s, hydrogen number 1); d5.35 and 6.23 (H, d,
due to hydrogen number 30);
hydrogen number 40).
d6.87–7.98 (15H, Ar and
n
d
d
4.2.4. 10-(4-Methylphenyl)-spiro{naphthalene-
1(2H),20(10H)-naphtho[2,1-b]furan}-2-one (3c and 4c)
J = 9.9 Hz and J = 10 Hz due to hydrogen number 30);
d6.63–
Yellow solid, yield 70%; IR (
1H-NMR (500 MHz, CDCl3):
2.12 and 2.27 (3H, s);
and 5.37 (1H, s, hydrogen number 1); 5.55 and 6.28 (1H, d,
J = 9.99 Hz and J = 9.92 Hz due to hydrogen number 30);
6.66–7.89 (15H, Ar and hydrogen number 40).
n
max, cmꢂ1): 1680 (C5O).
7.96 (15H, Ar and hydrogen number 40).
d
d5.18
d
Acknowledgments
d
The authors gratefully acknowledge the financial
support for this work from the Bu-Ali Sina University,
Hamedan, Iran.
4.2.5. 10-(2,4-Dichlorophenyl)-spiro{naphthalene-
1(2H),20(10H)-naphtho[2,1-b]furan}-2-one (3d and 4d)
Yellow solid, yield 73%; IR (
1H-NMR (90 MHz, CDCl3):
5.52 and 5.63 (1H, s, hydrogen
number 1); 5.58 and 6.23 (1H, d, both J = 10 Hz due to
n
max, cmꢂ1): 1683 (C5O).
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d
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1(2H),20(10H)-naphtho[2,1-b]furan}-2-one (3e and 4e)
Yellow solid, yield 82%; IR (
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3.64 and 3.75 (3H, s);
5.57 and 6.26 (H, d,
n
max, cmꢂ1): 1684 (C5O).
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J = 9.9 Hz and J = 10 Hz due to hydrogen number 30);
d6.48–
7.93 (15H, Ar and hydrogen number 40).
4.2.7. 10-(4-Fluorophenyl)-spiro{naphthalene-1(2H),20(10H)-
naphtho[2,1-b]furan}-2-one (3f and 4f)
Yellow solid, yield 78%; IR (
1H-NMR (500 MHz, CDCl3):
hydrogen number 1);
n
d
max, cmꢂ1): 1676 (C5O).
5.19 and 5.38 (1H, s,
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d
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naphtho[2,1-b]furan}-2-one (3g and 4g)
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5.48 and 5.59 (1H, s, hydrogen
number 1); 5.53 and 6.26 (1H, d, both J = 10 Hz due to
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d
d
hydrogen number 30);
number 40).
d6.57–7.98 (15H, Ar and hydrogen
4.2.9. 10-(3-Methylphenyl)-spiro{naphthalene-
1(2H),20(10H)-naphtho[2,1-b]furan}-2-one (3h and 4h)
Yellow solid, yield 75%; IR (
1H-NMR (90 MHz, CDCl3):
2.14 and 2.29 (3H, s);
5.56 and 6.27 (H, d,
n
max, cmꢂ1): 1687(C5O).
d
d5.19
and 5.38 (1H, s, hydrogen number 1);
d
J = 9.9 Hz and J = 10 Hz due to hydrogen number 30);
d6.47–
7.97 (15H, Ar and hydrogen number 40).
Please cite this article in press as: Khorramabadi-zad A, et al. Aerial oxidation of bisnaphthols to spironaphthalenones
by a recyclable magnetic core-sell nanoparticle-supported TEMPO catalyst. C. R. Chimie (2013), http://dx.doi.org/
10.1016/j.crci.2013.02.002