Aerobic catalytic oxidative coupling of 2-naphthols and phenols by VO(acac)2

Article abstract of DOI:10.1039/a901934k

In the presence of a catalytic amount of VO(acac)₂, oxidative coupling of 2-naphthol or phenol derivatives with molecular oxygen occurred at room temperature and selectively gave the corresponding ortho-ortho coupling products in moderate to high yields.

Full text of DOI:10.1039/a901934k

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Aerobic catalytic oxidative coupling of 2-naphthols and phenols by VO(acac)2
Der-Ren Hwang, Cheu-Pyeng Chen and Biing-Jiun Uang*
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 300, Republic of China.
E-mail: bjuang@chem.nthu.edu.tw
Received (in Cambridge, UK) 10th March 1999, Accepted 17th May 1999
In the presence of a catalytic amount of VO(acac)2, oxidative
coupling of 2-naphthol or phenol derivatives with molecular
oxygen occurred at room temperature and selectively gave
the corresponding ortho–ortho coupling products in moder-
ate to high yields.
of electron-donating and electron-withdrawing group substi-
tuted 2-naphthols was apparently different. Coupling of 1c was
finished within 9 h, but gave a lower yield due to the formation
of some intractable materials. The coupling reaction of
3-(methoxycarbonyl)-2-naphthol 1d was very sluggish. It gave
a 35% yield of 2d after 120 h, and 62% of 1d was recovered
(Table 1).
Optically active 1,1A-bi-2-naphthol and its derivatives have been
widely used in enantioselective synthesis as a source of
chirality.1 There are some known methods for the oxidative
coupling of 2-naphthols to give 1,1A-bi-2-naphthols using
stoichiomeric amounts of oxidant,2–4 and some methods
employing catalytic oxidative coupling. These methods either
use an expensive oxidant (such as AgCl) with low yield,4c
require the preparation of a complex catalyst [such as
CuCl(OH)·TMEDA, CuSO4(Al2O3)] before the coupling reac-
tion,5,6 or perform the reaction at higher temperature [Cu-
SO4(Al2O3), FeCl3].2a Oxovanadium complexes were found to
have specific catalytic activity towards organic syntheses
especially in oxidation reactions.7 A vast number of synthetic
reactions which utilize oxovanadium(v), i.e. VOCl3 and VOF3,
as oxidants have been documented, as exemplified by the
oxidative coupling of phenols in natural product synthesis.8 Due
to the fact that VOCl3 and VOF3 are moisture sensitive,
hazardous materials,9 they are not easy to use in practice. Thus
it is important to find a more convenient method for the
oxidative coupling of phenols. Here we report a convenient
oxidative coupling method for 2-naphthols and phenols with
molecular oxygen as the oxidant in the presence of a catalytic
amount (10 mol%) of VO(acac)2, an inexpensive and stable
catalyst (Scheme 1).10
Table 1 Oxidative coupling of 2-naphthol and derivatives catalyzed by
VO(acac)2
a
Napthol
R1
R2
R3
t/h
24
24
9
Productb Yield (%)
1a
1b
1c
1d
a
H
Br
H
H
H
H
OMe
H
H
H
H
2a
2b
2c
2d
92
90
76
35
CO2Me 120
The reactions were run with 10 mol% VO(acac)2 in CH2Cl2 at room
temperature under 1 atm O2. b Compounds 2a–d were identified according
to data reported in ref. 6.
Coupling of phenol under similar reaction conditions was
unsuccessful; there was no detectable amount of 1,1A-biphenol
present. When 2,4-dimethylphenol 3a and 2,3,5-trimethylphe-
nol 3b were subjected to the coupling reaction, the correspond-
Me
Me
OH
Me
Me
OH
Me
3a
3b
R1
R3
R1
R2
R3
Me
OH
OH
VO(acac)2 (cat.), oxidant
R2
R2
Me
Me
Me
Me
OH
R1
R3
1a–d
Me
Me
OH
OH
OH
OH
2a–d
Scheme 1
To achieve a catalytic cycle in the vanadium mediated
coupling of phenols, one has to find an oxidant which will
oxidize VIV to VV and will not interfere with the coupling
reaction during the catalytic cycle. At the outset, a system
consisting of 2-naphthol 1a, 10 mol% VO(acac)2 and oxidants
such as H2O2, ButOOH and Oxone was studied. Although
2-naphthol was consumed completely in these cases, only trace
amounts of the coupling product 2a were detected. The
remaining materials were intractable. Then, NaIO4 and NH4IO4
were used as oxidants. After reaction for 24 h under similar
reaction conditions, most of the starting material was recovered
and there was no coupling product. Finally, when molecular
oxygen was used as oxidant and the reaction was conducted in
CH2Cl2 at room temperature for 24 h, 1a was consumed and 2a
was obtained in 92% yield after chromatographic purification.†
The coupling product was present only in trace amounts when
the reaction was conducted in MeOH.
Me
Me
Me
4a
4b
ing ortho–ortho coupling products 4a and 4b were obtained in
moderate yields (Table 2). These two reactions are similar in
terms of reaction rate. Prolonged reaction time did not give a
better yield of coupling product. In the latter case, 28% of 3b
Table 2 Oxidative coupling of alkyl substituted phenols catalyzed by
a
VO(acac)2
Phenol
t/h
Productb
Yield (%)
3a
3b
120
48
4a
4b
66
62
b
a
Reaction conditions were similar to those for 1a–d.
characterized according to data reported in ref. 11.
4a,b were
In the case of 6-bromo-2-naphthol 1b, the coupling reaction
was completed in 24 h to give 2b in 90% yield. The reactivity
Chem. Commun., 1999, 1207–1208
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2 (a) F. Toda, K. Tanaka and S. Iwata, J. Org. Chem. 1989, 54, 3007; (b)
R. Pummerer, E. Prell and A. Rieche, Ber., 1926, 59, 2159; (c) B.
Feringa and H. Wynberg, J. Org. Chem., 1981, 46, 2547.
3 M. J. S. Dewar and T. Nakaya, J. Am. Chem. Soc., 1968, 90, 7134; K.
Yamamoto, H. Fukushima, Y. Okamoto, K. Hatada and M. Nakazaki,
J. Chem. Soc., Chem. Commun., 1984, 1111.
4 (a) B. Feringa and H. Wynberg, Tetrahedron Lett., 1977, 18, 4447; (b)
J. Brussee, J. L. G. Groenendijk, J. M. te Koppele and A. C. A. Jansen,
Tetrahedron, 1985, 41, 3313; (c) M. Smrcina, J. Polakova, S. Vyskocil
and P. Kocovsky, J. Org. Chem., 1993, 58, 4534.
was recovered. Reaction of 3a for 120 h gave a similar yield of
4a but no 3a was recovered. Instead, some intractable material
was formed.
In conclusion, a facile oxidative coupling method that
selectively coupled 2-naphthol or phenol derivatives to the
corresponding ortho–ortho coupling products, 1,1A-bi-2-naph-
thols or 1,1A-bi-2-phenols, with molecular oxygen in the
presence of a catalytic amount of VO(acac)2 in moderate to high
yields has been demonstrated.
5 M. Noji, M. Nakajima and K. Koga, Tetrahedron Lett., 1994, 35,
7983.
We are grateful to the National Science Council, Republic of
China, for support of this work.
6 T. Sakamoto, H. Yonehara and C. Pac, J. Org. Chem.,1994, 59, 6859.
7 For a recent review see: T. Hirao, Chem. Rev., 1997, 97, 2707.
8 M. A. Schwartz, R. A. Holton and S. W. Scott, J. Am. Chem. Soc., 1969,
91, 2800; J. D. White, R. J. Butlin, H.-G. Hahn and T. Johnson, J. Am.
Chem. Soc., 1990, 112, 8595; D. A. Evans, C. J. Dinsmore, D. A. Evrard
and K. M. DeVries, J. Am. Chem. Soc., 1993, 115, 6426; D. L. Comins
and L. A. Morgan, Tetrahedron Lett., 1991, 32, 5919; W. L. Carrick,
G. L. Karapinka and G. T. Kwiatkowski, J. Org. Chem., 1969, 34,
2388.
9 M. K. O’Brien and B. Vanasse, in Encyclopedia of Reagents for
Organic Synthesis, ed. L. A. Paquette, Wiley, New York, 1995, vol. 8,
pp. 5482–5485.
10 B. E. Rossiter, in Encyclopedia of Reagents for Organic Synthesis, ed.
L. A. Paquette, Wiley, New York, 1995, vol. 8, pp. 5479–5482.
11 For 4a see: G. Sartori, R. Maggi, F. Bigi, A. Arienti, G. Casnati, G.
Bocelli and G. Mori, Tetrahedron, 1992, 48, 9483; for 4b see: D. R.
Armstrong, C. Cameron, D. C. Nonhebel and P. G. Perkins, J. Chem.
Soc., Perkin Trans. 2 1983, 581.
Note and references
† Typical procedure: A stirred mixture of 2-naphthol (144 mg, 1 mmol), and
VO(acac)2 (26.5 mg, 0.1 mmol) in CH2Cl2 (10 ml) was exposed under an
atmospheric pressure of molecular oxygen at room temperature for 24 h.
The mixture was then filtered through a short column of silica gel and the
silica gel was washed with EtOAc (40 ml). The filtrate was concentrated and
purified by column chromatography (SiO2, hexane–EtOAc = 5+1) to afford
the coupling product 2a (131 mg, 92%, mp 215–217 °C ; lit., 4a 216–218
°C). On a 100 mmol scale, 75–78% of the coupling product was
obtained.
1 For recent reviews see: C. Rosini, L. Franzini, A. Raffaelli and P.
Salvadori, Synthesis, 1991, 503; H. B. Kagan and O. Riant, Chem. Rev.,
1992, 92, 1007; K. Mikami and M. Shimizu, Chem. Rev., 1992, 92,
1021; (d) L. Pu, Chem. Rev., 1998, 98, 2405.
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