Green and diasteroselective oxidative cyclization of bisnaphthols to spirans

Article abstract of DOI:10.1007/BF03246020

Hydrogen peroxide/MoO₃, as an efficient and clean oxidizing system was used to afford diasteroselective oxidative cyclization of bisnaphthols to spirans in ethanol at 60 °C with high yields. Bisnaphthols were prepared by the reaction of a series of aldehydes and 2-naphthol in the presence of a catalytic amount of H₃[P(Mo₃O ₁₀)₄].nH₂O (HPA) in refluxing dichloromethane.

Full text of DOI:10.1007/BF03246020

J. Iran. Chem. Soc., Vol. 7, No. 2, June 2010, pp. 351-358.
JOUIRrNaAnLiaOnF THE
Chemical Society
Green and Diasteroselective Oxidative Cyclization of Bisnaphthols to Spirans
A. Alizadeh*, M.M. Khodaei* and K.H. Moradi
Department of Chemistry, Razi University, Kermanshah 67149, IR, Iran
(Received 20 January 2009, Accepted 11 June 2009)
Hydrogen peroxide/MoO3, as an efficient and clean oxidizing system was used to afford diasteroselective oxidative cyclization
of bisnaphthols to spirans in ethanol at 60 °C with high yields. Bisnaphthols were prepared by the reaction of a series of aldehydes
and 2-naphthol in the presence of a catalytic amount of H3[P(Mo3O10)4].nH2O (HPA) in refluxing dichloromethane.
Keywords: Bisnaphtols, Spirans, MoO3, Hydrogen peroxide, HPA
INTRODUCTION
fact substitution reactions rather than with "one-electron"
oxidants [4]. A literature survey revealed that there was no
report on utilizing green oxidants to afford spirans and
therefore, using a green oxidizing agent such as H2O2 for this
oxidation reaction would be desirable.
Aqueous hydrogen peroxide is an attractive oxidant
because it is cheap, safely stored and handled, environmentally
friendly, contains effective oxygen and produces only water as
a byproduct, which is easy to deal with after reactions. There
are many reports on oxidation reactions carried out by a
combination of H2O2, and a catalyst that often increase the
efficiency of the oxidant.
Aryldi-(2-hydroxy-1-naphthyl)methanes (1) have been
synthesized by the reaction of aldehydes with 2-naphthol in
the presence of acids [6]. On the other hand,
aryldibenzoxanthenes have been synthesized without the
intermediacy of aryldi-(2-hydroxy-1-naphthyl)methanes by
heating the corresponding aldehydes and 2-naphthol in acetic
acid/hydrochloric acid [7] or in the presence of a catalyst under
neat conditions [8]. Despite these references for the
preparation of dibenzoxanthenes, the literature survey shows
that there are few reports on the synthesis of aryldi-(2-
hydroxy-1-naphthyl)methanes from aldehydes and 2-naphthol.
In continuation of our research on the oxidation of organic
compounds [8], we report here our experiments in developing
Oxidative cyclization of bisnaphthols [aryldi-(2-hydroxy-
1-naphthyl)methanes] (1) to spirans {arylnaphtho[2,1-b]furan-
2(1H)-spiro-1'(2'H)-naphthalen-2'-one} (2,3) (Scheme 1) is an
important reaction in biosynthesis of certain plant products
[1]. Several oxidizing reagents for oxidation of bisnaphthols
have been used to afford spirans. Dischendorfer used alkaline
hypobromite to oxidize the bisnaphthol to a compound shown
to be the spiran (2) in which the phenyl substituent was on the
side of the molecule away from the carbonyl group [2]. It was
also shown that some oxidants could produce the geometrical
isomer (3) with the phenyl substituent on the same side as the
carbonyl group [3]. Such a control over the stereochemistry is
quite novel in oxidative cyclizations. Dean and co-workers
discovered that a few oxidants were highly specific for one
geometrical isomer or the other, though many had no
specificity [4]. In their extended study, a selection of oxidants
was used whose results showed that the reagents commonly
used for phenolic coupling (and also peroxidase) had little
specificity. It was also revealed that specificity was associated
with "two-electron" oxidants operating through what are in
*Corresponding authors. E-mail: ahalizadeh2@hotmail.com
and mmkhoda@razi.ac.ir

Alizadeh et al.
R
R
R
MoO3
H2O2
H
H
+
+
C2H5OH
O
O
O
OH
OH
O
1
2
3
Scheme 1
new procedures for oxidation of aryldi-(2-hydroxy-1-
naphthyl)methanes (1) using our oxidizing system [5],
aqueous hydrogen peroxide catalyzed by MoO3 (Scheme 1).
7.0-7.9 (m, 15H). Compound 3a: IR (neat): 1670, 1616, 1482,
1
1455, 1238, 1078, 1020 cm-1; H NMR (CDCl3) ꢀ (ppm): 5.2
(s, 1H), 5.6 (d, 1H), 7.0-7.8 (m, 15H); 13C NMR (CDCl3) ꢀ
(ppm): 197.9, 158.8, 143.5, 136.5, 133.7, 131.1, 130.3, 130.2,
129.4, 129.0, 128.7, 127.9, 126.8, 125.3, 124.0, 123.2, 122.5,
117.8, 117.1, 111.8, 94.9, 63.9.
EXPERIMENTAL
General Procedure for the Preparation of
Bisnaphthols from 2-Naphthol in the Presence of
HPA
(Table 3, Entry 2):
Compound 2b: IR (neat): 1680, 1628, 1462, 1372, 1043, 1030
1
cm-1; H NMR (CDCl3) ꢀ (ppm): 5.9 (s, 1H), 6.3 (d, 1H), 6.4
In a round bottomed flask (25 ml) equipped with a
condenser, a mixture of 2-naphthol (2 mmol), aldehyde (1
mmol) and HPA (0.04 mmol) in 1 ml dichloromethane was
stirred magnetically at 40 °C for the time specified in Table 1.
The progress of the reaction was followed by TLC. After the
completion of the reaction, water (20 ml) was added to the
reaction mixture and filtered. The solid residue was purified
on a silica gel plate (eluent:n-hexane/EtOAc:10/3) to afford
the pure bisnaphthol in excellent yield.
(d, 1H), 7.0-8.0 (m, 14H); 13C NMR (CDCl3) ꢀ (ppm): 198.2,
158.5, 145.0, 143.3, 134.8, 134.3, 134.0, 132.7, 131.2, 130.2,
129.4, 129.3, 129.0, 128.9, 128.8, 127.1, 124.6, 123.8, 123.4,
122.3, 119.9, 117.5, 94.5, 58.3. Compound 3b: IR (neat):
1680, 1628, 1462, 1372, 1043, 1030 cm-1; 1H NMR (CDCl3) ꢀ
(ppm): 5.6 (s, 1H), 5.8 (s, 1H), 6.7 (d, 1H), 7.0-8.0 (m, 14H);
13C NMR (CDCl3) ꢀ (ppm): 198.2, 158.5, 145.0, 143.3, 134.8,
134.3, 134.0, 132.7, 131.2, 130.2, 129.4, 129.3, 129.0, 128.9,
128.8, 127.1, 124.6, 123.8, 123.4, 122.3, 119.9, 117.5, 94.5,
58.3.
General Procedure for the Preparation of Spirans
from Bisnaphthol with H2O2/MoO3 System as
Oxidizing Agent
(Table 3, Entry 5):
Compound 2e: IR (neat): 1674, 1622, 1454, 1370, 1038, 1025
1
cm-1; H NMR (CDCl3) ꢀ (ppm): 6.0 (s, 1H), 6.2 (d, 1H), 6.4
In a round bottomed flask (50 ml) equipped with a
condenser, a solution of substituted benzylidene-1,1'-bis-2-
naphthol (1 mmol) in ethanol (1.5 ml) was prepared. Then,
30% H2O2 (1 ml), and MoO3 (1 mmol) were added. The
mixture was stirred magnetically at 60 °C for the appropriate
time. The progress of the reaction was followed by TLC. After
the completion of the reaction, water (20 ml) was added to the
reaction mixture and filtered. The solid residue was
recrystallized from EtOH to afford the pure product.
Selected spectroscopic data of spirans:
(d, 1H), 7.1-7.9 (m, 14H); 13C NMR (CDCl3) ꢀ (ppm): 198.4,
158.8, 145.3, 143.7 135.0, 134.6, 134.5, 132.9, 131.5, 130.5,
129.6, 129.4, 129.2, 129.0, 128.9, 127.4, 124.9, 124.5, 123.9,
123.6, 123.3, 122.5, 120.2, 117.8, 94.7, 58.5. Compound 3e:
IR (neat): 1674, 1622, 1454, 1370, 1038, 1025 cm-1; H NMR
1
(CDCl3) ꢀ (ppm): 5.6 (d, 1H), 5.8 (s, 1H), 6.7 (d, 1H), 7.1-7.9
(m, 14H); 13C NMR (CDCl3) ꢀ (ppm): 198.6, 158.9, 145.5,
143.9, 135.2, 134.8, 134.9, 133.1, 131.6, 130.8, 129.8, 129.5,
129.5, 129.1, 129.0, 127.7, 125.1, 124.6, 124.2, 123.8, 123.4,
122.6, 120.3, 117.8, 94.9, 58.9.
(Table 3, Entry 1):
(Table 3, Entry 7):
Compound 2a: IR (neat): 1677, 1628, 1484, 1459, 1248, 1088,
Compound 2g: IR (neat): 1685, 1630, 1465, 1370, 1040, 1028
1
1024 cm-1; 1H NMR (CDCl3) ꢀ (ppm): 5.4 (s, 1H), 6.5 (d, 1H),
cm-1; H NMR (CDCl3) ꢀ (ppm): 2.2 (s, 3H), 5.4 (s, 1H), 6.3
352

Green and Diasteroselective Oxidative Cyclization of Bisnaphthols
(d, 1H), 7.0-7.9 (m, 15H); 13C NMR (CDCl3) ꢀ (ppm): 198.5,
synthesized efficiently by reaction of aromatic aldehydes with
2-naphthol in the presence of catalytic amounts of
H3[P(Mo3O10)4]-nH2O (HPA) in refluxing dichloromethane
(Scheme 2, Table 1). The experimental procedure for this
reaction was remarkably simple and required no toxic organic
solvents or inert atmospheres. However, the synthesis could
not have been achieved in the absence of the catalyst. The
reactions were complete in 1 h. The aromatic aldehydes
containing electron-donating or electron-withdrawing groups
underwent the conversion equally. It was observed that the
yields of the products of aromatic aldehydes with substituents
in 2-positions were low, while 2-nitrobenzaldehyde gave the
corresponding product in high yield (Table 1, entry 2).
158.9, 145.6, 143.1, 138.8, 136.6, 134.6, 131.0, 130.5, 130.1,
129.3, 129.0, 128.9, 128.5, 128.2, 127.9, 127.5, 126.6, 124.8,
123.0, 122.9, 116.7, 111.7, 95.7, 59.1, 20.8. Compound 3g: IR
1
(neat): 1685, 1630, 1465, 1370, 1040, 1028 cm-1; H NMR
(CDCl3) ꢀ (ppm): 2.3 (s, 1H), 5.2 (s, 1H), 5.6 (d, 1H), 7.0-7.9
(m, 15H); 13C NMR (CDCl3) ꢀ (ppm): 198.4, 158.4, 143.8,
143.1, 137.4, 134.9, 130.7, 130.5, 130.2, 130.1, 129.3, 129.0,
128.8, 128.5, 126.6, 125.4, 124.8, 123.0, 122.8, 117.8, 119.9,
111.8, 95.2, 64.3, 21.0.
RESULTS AND DISCUSSION
First,
aryldi-(2-hydroxy-1-naphthyl)methanes
were
From among several possible oxidants, MoO3 was chosen
R
H
O
OH
HPA (0.04 mmol)
CH2Cl2, reflux
+
R
R
OH
OH
(1)
Scheme 2
Table 1. Synthesis of Arylmethanebisnaphtholsa from Aromatic Aldehydes and 2-Naphthol in the Presence of the
Catalytic Amounts of HPA in CH2Cl2 under Reflux Conditions
Entry
Aldehyde
Productb
M.p. (ºC)
Yield (%)c
Found
Reported
Cl
H
O
1
190
187.5-188
94
Cl
O
OH
OH
H
NO2
NO2
2
206-208
205-207
95
OH
OH
353

Alizadeh et al.
Table 1. Continued
NO2
H
O
3
189-190
178
189-191
97
60
NO2
OH
OH
OMe
H
O
4
5
6
7
-
OMe
OH
OH
OH
OH
F
H
O
110
165
153
109-110
65
85
55
F
OH
Me
H
O
-
-
Me
OH
Cl
H
O
Cl
Cl
Cl
OH
OH
OH
H
O
OMe
OMe
8
9
191
200
189-190
59
51
OH
H
O
-
OH
OH
354

Green and Diasteroselective Oxidative Cyclization of Bisnaphthols
Table 1. Continued
H
O
OMe
10
N.R
-
-
-
-
-
OMe
H
O
OH
11
12
<10
OH
OH
OH
OH
H
O
Cl
130
-
45
Cl
OH
1
aThe reaction time is 1 h. bThe products were characterized by comparison of their melting points and H NMR and
13C NMR spectroscopic data with those reported in literature. CIsolated yields.
Table 2. The Catalyst Amount and Solvent Effect on the Oxidative Reaction of Phenyldi-(2-hydroxy-1-
naphthyl)methane with H2O2/MoO3 System
Entry
Oxidizing system
MoO3 (%mol)
Solvent
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
H2O2
MoO3
0
EtOH
EtOH
CH3CN
ClCH2CH2Cl
EtOH
CH3COOC2H5
EtOH
CH3COCH3
10
10
3
3
3
3
3
3
N.Rb
N.Rb
30
10
62
10
85
65
100
100
100
50
100
100
100
H2O2/MoO3
H2O2/MoO3
H2O2/MoO3
H2O2/MoO3
H2O2/MoO3
H2O2/MoO3
aIsolated yield. bNo reaction.
based on our recent study utilizing hydrogen peroxide together
with MoO3 as an efficient and chemoselective oxidative
system in oxidizing sulfides [5]. After examining various
amounts of MoO3, we found that one equivalent of MoO3 was
the best choice. The effect of solvents on the oxidation
reaction was also examined by the reaction of phenyldi-(2-
hydroxy-1-naphthyl)methane with H2O2/MoO3 in different
solvents at 60 °C and it was found that EtOH was the best
solvent (Table 2).
A range of aryldi-(2-hydroxy-1-naphthyl)methanes with
355

Alizadeh et al.
different substituents was subjected to the developed reaction
neutral conditions. In addition, the results in Table 3 indicate
that the electronic effects in the phenyl substituent hardly
affected the orientation of the reaction. Therefore, the
selectivity is presumed to be caused mainly by steric effects.
procedure to afford the products with high diasteroselectivity
and high yields. It proved to be compatible with some
functional groups on aromatic aldehyde and proceeded under
Table 3. Synthesis of Spirans from Bisnaphthols Using H
2O2/MOO3 System in EtOH at 60 ºC
M.p. (°C)
Total yield
Yield(2)/Yield
(3)
Entry
1
Substract
Product 2
Product 3
Found
Reported [Ref.]
2
3
2
3
Cl
Cl
Cl
264
239
-
-
85
25/27
H
O
H
O
OH
F
OH
O
O
3a
2a
F
F
2
144
214 145 [4] 214 [4]
92
20/80
H
H
O
OH
OH
3b O
O
O
2b
NO2
NO2
NO2
3
4
225
196
241 227 [4] 241 [4]
226 195 [4] 227 [4]
85
40/60
H
H
OH
OH
O
O
2c
O
3c
O
OMe
OMe
MeO
58
63/37
H
H
OH
3d O
OH
O
O
O
2d
CL
CL
CL
CL
CL
CL
5
195
204
-
-
65
25/75
H
H
3eO
OH
OH
2e O
O
O
356

Green and Diasteroselective Oxidative Cyclization of Bisnaphthols
Table 3. Continued
OMe
OMe
OMe
6
195
155
230 194 [4] 229 [4]
55
65/35
H
H
OH
OH
O
O
3f
O
2f
Me
O
Me
Me
7
228
-
-
67
48/52
H
H
OH
OH
3gO
2gO
O
O
O
Interestingly,
2,4-dimethoxybenzaldehyde
gave
no
Mo
O
MoO3
H2O2
H
O
O
+
O
corresponding product under the same reaction conditions.
H
The products were characterized by comparing their
melting points and H NMR and 13C NMR spectroscopic data
1
with those reported in literature. In all cases, less than 15% of
xanthenes were obtained.
1
The structural assignments were examined by H NMR
and 13C NMR studies. The geometrical isomers (2) showed a
doublet around 6.1 ppm (vinylic hydrogen), while the other
isomers (the less hindered isomers) (3) indicated a resonance
of nearly 5.4 ppm. In addition, the geometrical isomers (2)
were yellow in color, while the other isomers (3) were pale
yellow or cream. The ratio of 2/3 changed from 0.25 to 0.67.
The products (2) and (3) were not affected by the oxidant
when the reactions continued for a longer period.
OH OH
O
O
(1)
Mo
O
O
H
O
H
O
Mo
O
O-
O
H
O
O
O
H
HOO-
HMoO3
+
+
This observation reveals that the reactions are not
reversible. A tentative proposed mechanism for this oxidation
reaction is shown in Scheme 3.
H
O
O
(2 and 3)
Scheme 3
CONCLUSIONS
one diasteroselectively in the presence of H2O2/MoO3 system
in ethanol at 60 °C.
We have developed a method for the synthesis of aryldi-(2-
hydroxy-1-naphthyl)methanes from aromatic aldehydes and 2-
naphthol in the presence of the catalytic amounts of HPA in
refluxing CH2Cl2 in high yields in 1 h. Aryldi-(2-hydroxy-1-
naphthyl)methanes were efficiently and oxidatively cyclized
to arylnaphtho[2,1-b]furan-2(1H)-spiro-1’(2H)-naphthalen-2’-
ACKNOWLEDGEMENTS
The authors gratefully acknowledge the financial support
357

Alizadeh et al.
of this work by the Research Council of Razi University.
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M.M. Khodaei, K. Bahrami, M. Khedri, M. Can. J.
Chem. 85 (2007) 7.
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