Synthesis of 6-hydroxy-2-naphthoic acid from 2,6-diisopropylnaphthalene using NHPI as a key catalyst

Article abstract of DOI:10.1016/j.tet.2009.03.013

A new strategy to 6-hydroxy-2-naphthoic acid (HNPA) and 4-hydroxybenzoic acid from 2,6-diisopropylnaphthalene and p-cymene, respectively, was developed using the NHPI-catalyzed aerobic oxidation as a principal reaction. 2,6-Diisopropylnaphthalene was oxidized by the oxidation with O₂ (1 atm) by NHPI (10 mol %) combined with Co(OAc)₂ (0.5 mol %) to give 6-acetyl-2-isopropylnaphthalene, which then was converted to 6-isopropyl-2-naphthoic acid under O₂ (1 atm) in the presence of Co(OAc)₂ (0.5 mol %) and Mn(OAc)₂ (0.5 mol %). Esterification of the resulting acid followed by the aerobic oxidation produced methyl 6-hydroxy-2-naphthoate whose hydrolysis led to the desired HNPA. An alternative route involves the oxidation of 6-acetyl-2-isopropylnaphthalene to 6-acetyl-2-naphthol on which subsequent oxidation and deacetylation gave HNPA. This method was successfully extended to the synthesis of 4-hydroxybenzoic acid from p-cymene.

Full text of DOI:10.1016/j.tet.2009.03.013

Tetrahedron 65 (2009) 3577–3581
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of 6-hydroxy-2-naphthoic acid from 2,6-diisopropylnaphthalene
using NHPI as a key catalyst
*
Ryota Nakamura, Yasushi Obora, Yasutaka Ishii
Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering & High Technology Research Center, Kansai University,
Suita, Osaka 564-8680, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A new strategy to 6-hydroxy-2-naphthoic acid (HNPA) and 4-hydroxybenzoic acid from 2,6-diisopro-
pylnaphthalene and p-cymene, respectively, was developed using the NHPI-catalyzed aerobic oxidation
as a principal reaction. 2,6-Diisopropylnaphthalene was oxidized by the oxidation with O2 (1 atm) by
NHPI (10 mol %) combined with Co(OAc)2 (0.5 mol %) to give 6-acetyl-2-isopropylnaphthalene, which
then was converted to 6-isopropyl-2-naphthoic acid under O2 (1 atm) in the presence of Co(OAc)2
(0.5 mol %) and Mn(OAc)2 (0.5 mol %). Esterification of the resulting acid followed by the aerobic oxi-
dation produced methyl 6-hydroxy-2-naphthoate whose hydrolysis led to the desired HNPA. An alter-
native route involves the oxidation of 6-acetyl-2-isopropylnaphthalene to 6-acetyl-2-naphthol on which
subsequent oxidation and deacetylation gave HNPA. This method was successfully extended to the
synthesis of 4-hydroxybenzoic acid from p-cymene.
Received 10 February 2009
Received in revised form 4 March 2009
Accepted 5 March 2009
Available online 9 March 2009
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
6-Hydroxy-2-naphthoic acid (HNPA) (1) is a very important
class of compound as polymer materials for polyesters and
polymeric liquid crystals having high performance properties
like thermal stability.1 HNPA (1) is merely prepared by the
Kolbe–Schmitt reaction, which is a carboxylation of alkali and
alkaline earth metal naphthoxides with CO2.2 The drawback of
this method is the formation of a regioisomeric mixture of 2-
hydroxy-1-naphthoic acid, 2-hydroxy-3-naphthoic acid, and
HNPA (1). To our knowledge, however, there has been little
study so far of HNPA (1) synthesis from readily available starting
materials in spite of their synthetic importance.3 Thus, our at-
tention has been paid to the synthesis of HNPA (1) from 2,6-
diisopropylnaphthalene (2), which is manufactured in large scale
in industry.
In a previous paper, we reported that phenol can be prepared by
the NHPI-catalyzed aerobic oxidation of isopropylbenzene
(cumene) followed by treating with dilute sulfuric acid.4 In this
paper, this methodology has been applied to introducing a phenolic
OH group to the naphthalene ring for the synthesis of HNPA (1).
Here we wish to propose new routes to HNPA (1) from 2 using the
NHPI-catalyzed aerobic oxidation as a key reaction.
The first synthetic approach to HNPA (1) from 2 is outlined in
Scheme 1. The oxidation of 2 with O2 was examined by using
NHPI/AIBN system, leading to isopropyl hydroperoxide on which
subsequent decomposition with Co(OAc)2 followed by the
hydrogenation on Pd/C gave 6-acetyl-2-isopropylnaphthalene (3).
The oxidation of the 3 with O2 by Co(OAc)2 and Mn(OAc)2 affor-
ded 6-isopropyl-2-naphthoic acid (4). Esterification of 4 to methyl
6-isopropyl-2-naphtoate (5) followed by the oxidation with O2
under the influence of NHPI and AIBN produces methyl 6-hy-
droxy-2-naphthoate (6), which is easily hydrolyzed to 1.
Table 1 shows the result for the oxidation of 2 by NHPI under
various reaction conditions. The oxidation of 2 by NHPI combined
with Co(OAc)2 in acetonitrile at 75 ꢀC for 6 h produced 3 in 31% yield
(29% isolated yield) and 6-isopropenyl-2-isopropylnaphthalene (7)
in 5% yield at 36% conversion (entry 1). When Mn(OAc)2 in place of
Co(OAc)2 was added to the catalytic system, the conversion of 2 was
increased to 51%. However, the reaction gave rise to 7, but not 3, as
a major product (48% yield) (entry 3). This indicates that the cata-
lytic potential of the Mn ion is very different from that of the Co ion.
In order to improve the conversion and selectivity to 3, the oxida-
tion of 2 by NHPI in the presence of both Mn(OAc)2 and Co(OAc)2
was examined, but the selectivity of 3 did not increase (entry 4). The
reaction in acetic acid resulted in low conversion of 2 (entry 5).
Previously, we observed similar phenomena in the NHPI-catalyzed
aerobic oxidation of p-cymene in acetic acid, because the acetic acid
can induce the decomposition of the resulting isopropyl
* Corresponding author. Tel.: þ81 6 6368 0793; fax: þ81 6 6339 4026.
E-mail address: ishii@ipcku.kansai-u.ac.jp (Y. Ishii).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.03.013

3578
R. Nakamura et al. / Tetrahedron 65 (2009) 3577–3581
Step 1
1) Co(OAc)2 (0.5 mol%)
100 °C, 1 h
NHPI (10 mol%)
AIBN (3 mol%)
CH3CN (3 mL) 2) conc. H2SO4 (30 mg)
75 °C, 3 h rt, 1 min
2 (1 atm)
O
O
2
60% Isolated yield (83% Conv.)
3
after hydrogenation with 10w%Pd/C (entry 7, Table 1)
Step 3
Step 2
Co(OAc)2 (0.5 mol%)
Mn(OAc)2 (0.5 mol%)
NHPI (10 mol%)
OH
0.3 M H2SO4 (1 mL)
rt, 1 h
AIBN (3 mol%)
AcOH (3 mL)
100 °C, 15 h
O2 (1 atm)
CH3CN (3 mL)
75 °C, 15 h
ROOC
ROOC
O2 (1 atm)
4: R=H
5: R=Me
6: R=Me
1: R=H
92% Isolated yield (99% Conv.)
without Co(OAc)2 or Mn(OAc)2
<1% yield
66% Isolated yield (80% Conv.)
i
ii, iii
Scheme 1. Synthesis of 6-hydroxy-2-naphthoic acid (HNPA) (1) from 2,6-diisopropylnaphthalene (2) (first approach). Reagents and conditions: (i) H2SO4 (50 mg), MeOH (20 mL),
at 100 ꢀC for 24 h, quant.; (ii) NaOH (120 mg), H2O (30 mL), at 90 ꢀC for 15 h; (iii) HCl (1 mL), quant.
Table 1
Oxidation of 2 to 3 with O2 by NHPI under various conditionsa
NHPI (10 mol%)
Co(OAc)2 (0.5 mol%) conc. H2SO4 (30 mg)
rt, 1 min
Solvent (3 mL)
Temp., Time
O2 (1 atm)
O
2
3
3 mmol
O
+
+
+
+
O
O
7
8
9
10
Yield/%b
Entry
Solvent
Temp/ꢀC
Time/h
Conv./%
3
7
8
9
10
1
2
CH3CN
CH3CN
CH3CN
CH3CN
AcOH
75
75
75
75
100
75
6
15
6
6
6
36
48
51
40
8
31(29)
30
Trace
26
6
31
5
7
48
4
1
11
3
Trace
1
nd
Trace
Trace
4
Trace
8
nd
nd
Trace
32
nd
nd
nd
nd
nd
11
3c
4d
5
6e
7e,f
CH3CN
CH3CN
3
3
93
83
75
62(60)
1
1
10
a
Compound 2 (3 mmol) was reacted under O2 (1 atm) in the presence of NHPI (10 mol %) and Co(OAc)2 (0.5 mol %) in CH3CN (3 mL) at 75 ꢀC for 3–15 h.
Numbers in parentheses show isolated yields.
Mn(OAc)2 (0.5 mol %) was used in place of Co(OAc)2.
Mn(OAc)2 (0.5 mol %) was added to the catalytic system.
NHPI (10 mol %) and AIBN (3 mol %) were used as catalysts, and the reaction mixture was treated with Co(OAc)2 (0.5 mol %) at 100 ꢀC for 1 h before the treatment with
b
c
d
e
sulfuric acid.
f
After the reaction, the reaction mixture was reacted under H2 (1 atm) in the presence of 10 wt % Pd/C (100 mg) in EtOAc (20 mL) at room temperature for 6 h. Approximately
10% of 2 was increased after hydrogenation.
hydroperoxide to phenol, which serves as a radical inhibitor.4 The
oxidation of 2 by NHPI combined with AIBN in acetonitrile at 75 ꢀC
for 3 h produced 3, 2-acetyl-6-isopropenylnaphthalene (9), and 2,6-
diacetylnaphthalene (10) in 31%, 32%, and 11% yields, respectively
(entry 6). In this oxidation, 3 was found to be further oxidized to 9.
In order to improve the yield of 3, the hydrogenation of the resulting
reaction mixture was carried out. Thus, 3 was obtained as a major
product in 60% isolated yield (entry 7). This is the first successful
conversion of isopropyl group to acetyl group on the naphthalene
ring. In this hydrogenation, 7 and 2,6-diisopropenylnaphthalene (8)
were converted into the starting 2, which can be recycled as the
starting material. We next tried the aerobic oxidation of 3 under O2
(1 atm) using Co(OAc)2 (0.5 mol %) and Mn(OAc)2 (0.5 mol %) in
acetic acid at 100 ꢀC for 15 h and gave 6-isopropyl-2-naphthoic acid
(4) in 92% isolated yield. When either Mn(OAc)2 or Co(OAc)2
was removed from the catalytic system, 4 was formed in poor yield
(<1%) (step 2). This indicates that remarkable synergy effect of Co
and Mn ions appeared in this aerobic oxidation, although such
a marked synergy effect of these metal ions was not observed in the
oxidation of 2 by the NHPI as shown in entry 4 of Table 1.
The methyl ester (5) was allowed to react with O2 (1 atm) under
the influence of AIBN (3 mol %) and NHPI (10 mol %) in acetonitrile
at 75 ꢀC for 15 h followed by treatment with dilute sulfuric acid at
room temperature for 1 h to lead to a mixture of 6 (66% isolated
yield), methyl 6-acetyl-2-naphthoate (11) (4%), and methyl 6-iso-
propenyl-2-naphthoate (12) (4%) at 80% conversion (step 3).
Treatment of 6 with a base gave rise to the desired 1 in quantitative
yield.
O
MeOOC
MeOOC
11
12

R. Nakamura et al. / Tetrahedron 65 (2009) 3577–3581
3579
NHPI (10 mol%)
AIBN (3 mol%)
Co(OAc)2 (0.5 mol%)
OR
OR
0.3 M H2SO4 (1 mL)
rt, 1 h
Mn(OAc)2 (0.5 mol%)
3
CH3CN (3 mL)
75 °C, 15 h
O2 (1 atm)
75% Isolated yield (90% Conv.)
AcOH (3 mL)
100 °C, 15 h
O2 (1 atm)
HOOC
O
13: R=H
15: R=Ac
1: R=H
66% Isolated yield (73% Conv.)
i
ii, iii
14: R=Ac
Scheme 2. Synthesis of 6-hydroxy-2-naphthoic acid (HNPA) (1) from 2,6-diisopropylnaphthalene (2) via 6-acetyl-2-naphthol (13) (second approach). Reagents and conditions:
(i) Ac2O (10 mL), Pyridine (10 mL), at 100 ꢀC for 15 h, quant.; (ii) NaOH (120 mg), H2O (30 mL), at 90 ꢀC for 15 h; (iii) HCl (1 mL), quant.
Scheme 2 shows another synthetic approach of 1 from 3. The
oxidation of 3 with O2 under the influence of catalytic amounts of
AIBN and NHPI in acetonitrile at 75 ꢀC for 15 h followed by treat-
ment with dilute sulfuric acid produced 6-acetyl-2-naphthol (13) in
85% yield (75% isolated yield) at 90% conversion. Acetylation of 13
with acetic anhydride and then the aerobic oxidation by Co(OAc)2
and Mn(OAc)2 gave 1 in 66% isolated yield at 73% conversion after
hydrolysis.
basis of the internal standard technique by using GC. All products
except 9 were known compounds and reported previously.5
3.1.1. 2-Acetyl-6-isopropenylnaphthalene (9)
1H NMR (270 MHz, CDCl3, Me4Si): 2.27 (s, 3H), 2.70 (s, 3H),
5.26 (s, 1H), 5.58 (s, 1H), and 8.41–7.66 (m, 6H); 13C NMR
(67.5 MHz, CDCl3, Me4Si): 21.8 (CH3), 26.5 (CH3), 114.4 (CH2), 124.2
(CH), 124.5 (CH), 124.8 (CH), 129.2 (CH), 131.6 (CH), 135.6 (CH),
140.9 (C), 142.5 (C), 144.7 (C), 145.4 (C), 150.5 (C), and 198.2 (C); IR
(neat, cmꢂ1) 3428, 2975, 1673, 1626, 1355, 1284, 1172, 1131, 889,
824, and 477; GC–MS (EI) m/z (relative intensity) 210 (Mþ, 57),
This strategy can be extended to the synthesis of 4-hydroxy-
benzoic acid (16), which is an important compound for drugs, dyes,
and polymer material, from p-cymene (17) (Scheme 3).
NHPI (10 mol%)
NHPI (10 mol%)
Co(OAc)2 (0.5 mol%)
OR
OR
0.3 M H2SO4 (1 mL)
rt, 1 h
AIBN (3 mol%)
Mn(OAc)2 (0.5 mol%)
CH3CN (3 mL)
75 °C, 15 h
O2 (1 atm)
42% Isolated yield (63% Conv.)
AcOH (3 mL)
100 °C, 15 h
O2 (1 atm)
HOOC
17
18: R=H
20: R=Ac
21: R=Ac
16: R=H
83% Isolated yield (90% Conv.)
i
ii, iii
Scheme 3. Synthesis of 4-hydroxybenzoic acid (16) from p-cymene (17). Reagents and conditions: (i) Ac2O (10 mL), Pyridine (10 mL), at 100 ꢀC for 15 h, quant.; (ii) NaOH (120 mg),
H2O (30 mL), at 90 ꢀC for 15 h; (iii) HCl (1 mL), quant.
The oxidation of 17 with O2 in the presence of AIBN and NHPI in
acetonitrile at 75 ꢀC for 15 h followed by treatment with dilute
sulfuric acid produced p-cresol (18) in 49% yield (42% isolated yield)
along with 4-isopropenyltoluene (19) in 13% yield at 63% conver-
sion. Acetylation of 18 to 4-acetoxytoluene (20) followed by the
oxidation in the presence of NHPI, Co(OAc)2, and Mn(OAc)2 and
then the treatment with 0.3 M sulfuric acid afforded 16 in 83%
isolated yield at 90% conversion.
195 (100%), 167 (40), 165 (22), 152 (24), 139 (5), 126 (5), and 115
(4); HRMS (EI) m/z calcd for C15H14O [Mþ] 210.1045, found
210.1049.
3.2. Synthesis of 6-hydroxy-2-naphthoic acid (HNPA) (1) from
2,6-diisopropylnaphthalene (2) (first approach, Scheme 1)
3.2.1. Synthesis of 6-acetyl-2-isopropylnaphthalene (3)
A mixture of 2,6-diisopropylnaphthalene (2) (637 mg, 3 mmol),
NHPI (49 mg, 0.3 mmol, 10 mol %), and AIBN (14.7 mg, 0.09 mmol,
3 mol %) in acetonitrile (3.0 mL) was placed in a 30 mL pear-shaped
flask equipped with a balloon filled with O2. The mixture was
stirred at 75 ꢀC for 3 h. The reaction mixture was treated with
Co(OAc)2$4H2O (3.7 mg, 0.015 mmol, 0.5 mol %) at 100 ꢀC for 1 h
under argon atmosphere. The reaction mixture was treated with
a sulfuric acid (30 mg) at room temperature for 1 min. Removal of
the solvent under reduced pressure afforded a crude mixture, and
10 wt % Pd/C (100 mg) in ethyl acetate (20 mL) was placed in
a 50 mL pear-shaped flask equipped with a balloon filled with H2.
The mixture was stirred at the room temperature for 6 h. Removal
of the solvent under reduced pressure afforded a crude mixture,
which was purified by column chromatography on silica gel
(n-hexane/AcOEt¼15/1) to give 6-acetyl-2-isopropylnaphthalene
(3) (382 mg, 1.8 mmol) in 60% isolated yield as a pure form.
19
In conclusion, a new approach to 6-hydroxy-2-naphthoic acid
and 4-hydroxyl benzoic acid from easily available starting materials
was achieved by using the NHPI-catalyzed aerobic oxidation as
a key reaction and obtained desired products in fair yields.
3. Experimental
3.1. General procedure
All solvents, 2 and 17 were purchased from commercial sources.
GC analysis was performed on GC equipped with a flame ionization
detector using a 0.22 mmꢁ25 m capillary column. Mass spectra
3.2.2. Synthesis of 6-isopropyl-2-naphthoic acid (4)
were determined at ionization energy of 70 eV on GC–MS.1H and 13
C
A mixture of 6-acetyl-2-isopropylnaphthalene (3) (637 mg,
NMR were measured at 270/400 MHz and 67.5/100 MHz, re-
spectively, in CDCl3 or DMSO-d6 with Me4Si as the internal standard.
TLC was performed on TLC plastic sheets F254 silica gel 60, using UV
light and I2. Infrared(IR) spectraweremeasured as thin filmson NaCl
plate. The product yields were estimated from the peak areas on the
3 mmol), Co(OAc)2$4H2O (3.7 mg, 0.015 mmol, 0.5 mol %), and
Mn(OAc)2$4H2O (3.6 mg, 0.015 mmol, 0.5 mol %) in acetic acid
(3.0 mL) was placed in a 30 mL pear-shaped flask equipped with
a balloon filled with O2. The mixture was stirred at 100 ꢀC for 15 h.
Removal of the solvent under reduced pressure afforded a crude

3580
R. Nakamura et al. / Tetrahedron 65 (2009) 3577–3581
mixture, which was extracted with NaHCO3 solution followed by work
up with hydrochloric acid (1 mL) to give 6-isopropyl-2-naphthoic acid
(4) (591 mg, 2.76 mmol) in 92% isolated yield as a pure form.
a balloon filled with O2. The mixture was stirred at 100 ꢀC for 15 h.
Removal of the solvent under reduced pressure afforded a crude
mixture, which was extracted with NaHCO3 solution followed by
extracted with HCl solution to give 6-acetoxy-2-naphthoic acid (15)
(152 mg, 0.66 mmol) in 66% isolated yield as a pure form.
3.2.3. Synthesis of methyl 6-isopropyl-2-naphthoate (5)
A mixture of 6-isopropyl-2-naphthoic acid (4) (214 mg, 1 mmol)
and sulfuric acid (50 mg) in methanol (20 mL) was placed in
a 50 mL pear-shaped flask. The mixture was stirred at 100 ꢀC for
24 h. Removal of the solvent under reduced pressure afforded
a crude mixture, which was purified by column chromatography on
silica gel (n-hexane/AcOEt¼15/1) to give methyl 6-isopropyl-2-
naphthoate in quantitative yield.
3.3.4. Synthesis of 6-hydroxy-2-naphthoic acid (1)
6-Acetoxy-2-naphthoic acid (15) (230 mg, 1 mmol) and NaOH
(120 mg, 3 mmol) in H2O (30 mL) were placed in a 50 mL pear-
shaped flask. The mixture was reacted at 90 ꢀC for 15 h followed by
work up with hydrochloric acid (1 mL) to give 6-hydroxy-2-naph-
thoic acid (1) in quantitative yield.
3.4. Synthesis of 4-hydroxy-2-benzoic acid (16) from
p-cymene (17) (Scheme 3)
3.2.4. Synthesis of methyl 6-hydroxy-2-naphthoate (6)
A mixture of methyl 6-isopropyl-2-naphthoate (5) (228 mg,
1 mmol), NHPI (16 mg, 0.1 mmol, 10 mol %), and AIBN (4.9 mg,
0.03 mmol, 3.0 mol %) in acetonitrile (3.0 mL) was placed in a 30 mL
pear-shaped flask equipped with a balloon filled with O2. The
mixture was stirred at 75 ꢀC for 15 h. The reaction mixture was
treated with a solution of sulfuric acid (29 mg, 0.3 mmol) in ace-
tonitrile (1 mL) at room temperature for 1 h. Removal of the solvent
under reduced pressure afforded a crude mixture, which was pu-
rified by column chromatography on silica gel (n-hexane/
AcOEt¼15/1) to give the products, methyl 6-hydroxy-2-naphthoate
(6) (133 mg, 0.66 mmol) in 66% isolated yield as a pure form.
3.4.1. Synthesis of p-cresol (18)
A mixture of p-cymene (17) (134 mg, 1 mmol), NHPI (16 mg,
0.1 mmol, 10 mol %), and AIBN (4.9 mg, 0.03 mmol, 3.0 mol %) in
acetonitrile (3.0 mL) was placed in a 30 mL pear-shaped flask
equipped with a balloon filled with O2. The mixture was stirred at
75 ꢀC for 15 h. The reaction mixture was treated with a solution of
sulfuric acid (29 mg, 0.3 mmol) in acetonitrile (1 mL) at room tem-
perature for 1 h. Removal of the solvent under reduced pressure
afforded a crude mixture, which was purified by column chroma-
tography on silica gel (n-hexane/AcOEt¼15/1) to give the products,
p-cresol (18) (45 mg, 0.42 mmol) in 42% isolated yield as a pure form.
3.2.5. Synthesis of methyl 6-hydroxy-2-naphthoic acid (1)
A mixture of 6-hydroxy-2-naphthoate (6) (202 mg, 1 mmol) and
NaOH (120 mg, 3 mmol) in H2O (30 mL) was placed in a 50 mL
pear-shaped flask. The mixture was stirred at 90 ꢀC for 15 h fol-
lowed by work up with hydrochloric acid (1 mL) to give 6-hydroxy-
2-naphthoic acid in quantitative yield.
3.4.2. Synthesis of 4-acetoxytoluene (20)
p-Cresol (18) (1081 mg, 10 mmol), in a mixture of acetic anhy-
dride and pyridine (10 mL/10 mL) was placed in a 50 mL pear-
shaped flask. The mixture was stirred at 100 ꢀC for 15 h. Removal of
the solvent under reduced pressure afforded a crude mixture,
which was extracted with HCl solution followed by extracted with
NaHCO3 solution to give the products, which was purified by col-
umn chromatography on silica gel (n-hexane/AcOEt¼15/1) to give
4-acetoxytoluene (20) in quantitative yield.
3.3. Synthesis of 6-hydroxy-2-naphthoic acid (HNPA) (1)
from 2,6-diisopropylnaphthalene (2) via 6-acetyl-2-naphthol
(13) (second approach, Scheme 2)
3.3.1. Synthesis of 6-acetyl-2-naphthol (13)
3.4.3. Synthesis of 4-acetoxybenzoic acid (21)
A mixture of 6-acetyl-2-isopropylnaphthalene (3) (1061 mg,
5 mmol), NHPI (82 mg, 0.5 mmol, 10 mol %), and AIBN (25 mg,
0.15 mmol, 3.0 mol %) in acetonitrile (3.0 mL) was placed in a 30 mL
pear-shaped flask equipped with a balloon filled with O2. The
mixture was stirred at 75 ꢀC for 15 h. The reaction mixture was
treated with a solution of sulfuric acid (29 mg, 0.3 mmol) in aceto-
nitrile (1 mL) at room temperature for 1 h. Removal of the solvent
under reduced pressure afforded a crude mixture, which was
purified by column chromatography on silica gel (n-hexane/
AcOEt¼15/1) to give the products, 6-acetyl-2-naphthol (13)
(698 mg, 3.75 mmol) in 75% isolated yield as a pure form.
A mixture of 4-acetoxytoluene (20) (150 mg, 1 mmol), Co(OAc)2$
4H2O (1.2 mg, 0.005 mmol, 0.5 mol %), and Mn(OAc)2$4H2O (1.2 mg,
0.005 mmol, 0.5 mol %) in acetic acid (3.0 mL) was placed in a 30 mL
pear-shaped flask equipped with a balloon filled with O2. The mixture
was stirred at 100 ꢀC for 15 h. Removal of the solvent under reduced
pressure afforded a crude mixture, which was extracted with NaHCO3
solution followed by work up with hydrochloric acid (1 mL) to give 4-
acetoxybenzoic acid (21) (150 mg, 0.83 mmol) in 83% isolated yield as
a pure form.
3.4.4. Synthesis of 4-hydroxybenzoic acid (16)
4-Acetoxybenzoic acid (21) (180 mg, 1 mmol) and NaOH
(120 mg, 3 mmol) in H2O (30 mL) were placed in a 50 mL pear-
shaped flask. The mixture was stirred at 90 ꢀC for 15 h followed by
work up with hydrochloric acid (1 mL) to give 4-hydroxybenzoic
acid (16) in quantitative yield.
3.3.2. Synthesis of 2-acetoxy-6-acetylnaphthalene (14)
6-Acetyl-2-naphthol (13) (559 mg, 3 mmol), in a mixture of
acetic anhydride and pyridine (10 mL/10 mL) was placed in a 50 mL
pear-shaped flask. The mixture was stirred at 100 ꢀC for 15 h.
Removal of the solvent under reduced pressure afforded a crude
mixture, which was extracted with HCl solution followed by
extracted with NaHCO3 solution to give the products, which was
purified by column chromatography on silica gel (n-hexane/
AcOEt¼15/1) to give 2-acetoxy-6-acetylnaphthalene (14) in quan-
titative yield.
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific
Research on Priority Areas ‘Advanced Molecular Transformation of
Carbon Resources’ from the Ministry of Education, Culture, Sports,
Science, and Technology, Japan, and ‘High-Tech Research Center’
Project for Private Universities: matching fund subsidy from the
Ministry of Education, Culture, Sports, Science, and Technology,
2005–2009, and Research Association for Ishii Oxidation
Technology.
3.3.3. Synthesis of 6-acetoxy-2-naphthoic acid (15)
A mixture of 2-acetoxy-6-acetylnaphthalene (14) (228 mg,
1 mmol), Co(OAc)2$4H2O (1.2 mg, 0.005 mmol, 0.5 mol %), and
Mn(OAc)2$4H2O (1.2 mg, 0.005 mmol, 0.5 mol %) in acetic acid
(3.0 mL) was placed in a 30 mL pear-shaped flask equipped with

R. Nakamura et al. / Tetrahedron 65 (2009) 3577–3581
3581
Compound 5: Zoeller, J. R.; Sumner, C. E. J. Org. Chem. 1990, 55, 319; (e) Com-
pound 6: Gao, Y.; Voigt, J.; Zhao, H.; Pais, G. C. G.; Zhang, X.; Wu, L.; Zhang, Z.-Y.;
Burke, T. R., Jr. J. Med. Chem. 2001, 44, 2869; (f) Compound 7: Aoki, Y.; Sakaguchi,
S.; Ishii, Y. Adv. Synth. Catal. 2004, 346, 199; (g) Compound 8: Minisci, F.;
Recupero, F.; Cecchetto, A.; Gambarotti, C.; Punta, C.; Paganelli, R.; Pedulli, G. F.;
Fontana, F. Org. Process Res. Dev. 2004, 8, 163; (h) Compound 10: Zaccheria, F.;
Ravasio, N.; Ercoli, M.; Allegrini, P. Tetrahedron Lett. 2005, 46, 7743; (i) Com-
pound 11: Ref. 5d; (j) Compound 12: Shishido, Y.; Nakao, K.; Nagayama, S.;
Tanaka, H.; Duncton, M. A. J.; Cox, M.; Kincaid, J.; Sahasrabudhe, K.; Estiarte-
Martinez, M. PCT Int. Appl., 2007, WO 2007133637; (k) Compound 13: Kim, H.
M.; Jung, C.; Kim, B. R.; Jung, S.-Y.; Hong, J. H.; Ko, Y.-G.; Lee, K. J.; Cho, B. R.
Angew. Chem., Int. Ed. 2007, 46, 3460; (l) Compound 14: Rajarathnam, D.; Nadar,
P. A. Int. J. Chem. Kinet. 2001, 33, 157; (m) Compound 15: Teoh, M. M.; Chung, T.-
S.; Pramoda, K. P. Synth. Met. 2004, 147, 191; (n) Compound 16: Kshirsagar, V. S.;
Vijayanand, S.; Potdar, H. S.; Joy, P. A.; Patil, K. R.; Rode, C. V. Chem. Lett. 2008, 37,
310; (o) Compound 18: Kianmehr, E.; Yahyaee, M.; Tabatabai, K. Tetrahedron Lett.
2007, 48, 2713; (p) Compound 19: Lebel, H.; Davi, M.; Dı´ez-Gonza´lez, S.; Nolan,
S. P. J. Org. Chem. 2007, 72, 144; (q) Compound 20: Moghadam, M.; Tangesta-
ninejad, S.; Mirkhani, V.; Mohammadpoor-Baltork, I.; Taghavi, S. A. J. Mol. Catal.
A: Chem. 2007, 274, 217; (r) Compound 21: Yeung, C. S.; Dong, V. M. J. Am. Chem.
Soc. 2008, 130, 7826.
References and notes
1. (a) De Ruijter, C.; Bos, J.; Boerstoel, H.; Dingemans, T. J. J. Polym. Sci., Part A: Polym.
Chem. 2008, 46, 6565; (b) Hsiue, L.-T.; Ma, C.-C. M.; Tsai, H.-B. J. Appl. Polym. Sci.
1995, 56, 471; (c) Nagata, M. High Perform. Polym. 2001, 13, S265; (d) Gao, P.; Lu,
X. H.; Chai, C. K. Polym. Eng. Sci. 1996, 36, 2771.
2. (a) Lindsey, A. S.; Jeskey, H. Chem. Rev. 1957, 57, 583; (b) Rahim, M. A.; Matsui, Y.;
Kosugi, Y. Bull. Chem. Soc. Jpn. 2002, 75, 619; (c) Kumagai, H.; Ueda, S.; Hori, T.
Nippon Kagaku Kaishi 1991, 170; (d) Iijima, T.; Iwase, T.; Yamaguchi, T. J. Jpn. Pet.
Inst. 2006, 49, 206; (e) Kolbe, H.; Lautemann, E. Justus Liebigs Ann. Chem. 1860,
113, 125; (f) Schmitt, R. J. Prakt. Chem. 1886, 31, 397.
3. (a) Minisci, F.; Recupero, F.; Fontana, F.; Bjørsvik, H.-R.; Liguori, L. Synlett 2002,
610; (b) Kantam, M. L.; Ranganath, K. V. S.; Sateesh, M.; Kumar, K. B. S.; Chou-
dary, B. M. J. Mol. Catal. A: Chem. 2005, 225, 15; (c) Melero, J. A.; van Grieken, R.;
Morales, G.; Nun˜o, V. Catal. Commun. 2004, 5, 131; (d) Klein, C. D. P.; Tabeteh, G.
F.; Laguna, A. V.; Holzgrabe, U.; Mohr, K. Eur. J. Pharm. Sci. 2001, 14, 167.
4. Fukuda, O.; Sakaguchi, S.; Ishii, Y. Adv. Synth. Catal. 2001, 343, 809.
5. (a) Compound 1: Serrano-Wu, M. H.; Regueiro-Ren, A.; St. Laurent, D. R.; Carroll,
T. M.; Balasubramanian, B. N. Tetrahedron Lett. 2001, 42, 8593; (b) Compound 3:
Zawadiak, J.; Orlinska, B.; Stec, Z. Fresenius’ J. Anal. Chem. 2000, 367, 502; (c)
Compound 4: Huebner, C. F.; Jacobs, W. A. J. Biol. Chem. 1947, 169, 211; (d)