Synthesis of binaphthyl derivatives through radical cation formation

Full text of DOI:10.1021/jo950814b

788
J . Org. Chem. 1996, 61, 788-792
reaction intermediates in reaction mechanism studies,
Syn th esis of Bin a p h th yl Der iva tives
th r ou gh Ra d ica l Ca tion F or m a tion
there have been few reports of a general synthetic
application using the coupling reaction of aromatic radi-
cal cations to obtain biaryls, probably because of their
high reactivity.
Mutsuo Tanaka,*,† Hideki Nakashima,‡
Masahiro Fujiwara,† Hisanori Ando,§ and Yoshie Souma†
On the other hand, NO+ is a remarkable, diverse
reagent not only for nitrosation9 and nitration10 but also
for oxidations that produce aromatic radical cations.11 It
is reported that NOBF4 catalytically oxidizes naphtha-
lene derivatives to give binaphthyl derivatives in the
presence of O2 under acidic conditions12 where the
formation of radical cations tends to be favorable.13
These results prompted us to study the coupling reaction
of aromatic radical cations to obtain biaryls under acidic
conditions.
Osaka National Research Institute, AIST, 1-8-31,
Midorigaoka, Ikeda, Osaka, 563, J apan,
Department of Applied Chemistry, Faculty of Engineering,
Osaka Institute of Technology, 5-16-1, Ohmiya, Asahi-ku,
Osaka, 535, J apan, and Research Institute of Innovative
Technology for the Earth, 9-2, Kizugawadai, Kizucho,
Soraku-gun, Kyoto, 619-02, J apan
Received May 1, 1995
In tr od u ction
In this paper, we report the catalytic coupling reaction
of naphthalene derivatives using NaNO2 with CF3SO3H,
the role of acids in this reaction, and the Scholl reaction
using SbF5.
Aromatic radical cations are well-known species in
electrochemical and gas phase reactions that produce
biaryls through a coupling reaction with aromatic com-
pounds, and the existence of aromatic radical cations in
the liquid phase has recently been proposed on the basis
of spectroscopic studies.1 Metal salts such as CuCl2,2
Resu lts a n d Discu ssion
Tl(OCOCF3)3,3 and Mn[CH(COCH3)2]3 and Lewis acids
4
Cou p lin g Rea ction of Na p h th a len e Der iva tives.
It is well-known that NO+ is easily produced by treat-
ment of NaNO2 with Brønsted acids. In this study, we
chose CF3SO3H as the Brønsted acid because a mixture
of NaNO2 and CF3SO3H in CH3CN gave a homogeneous
solution.14 When 1-methylnaphthalene (5 mmol) was
added to the solution of CH3CN (50 mL) with NaNO2 (0.5
mmol) and CF3SO3H (10 mmol) at 0 °C in air, the
coupling reaction of 1-methylnaphthalene took place to
produce 4,4′-dimethyl-1,1′-binaphthyl in 97% yield.15
Similarly, other naphthalene derivatives gave the cor-
responding binaphthyl derivatives as shown in Table 1.
Most substrates were converted to give binaphthyl
derivatives in good yields with high regioselectivity;
however, some substrates showed different tendencies.
The low yield of naphthalene was clearly caused by its
low reactivity because most of the naphthalene was
recovered after the reaction. On the contrary, 1-naphthol
was too reactive even at -78 °C for the formation of
biaryls and resulted only in unidentifiable oily products.
On the other hand, the deterioration of the yield and
regioselectivity in the cases of 2-methyl-, 2-ethyl-, 2,3-
dimethyl-, and 2,6-dimethylnaphthalene seems to be
caused by steric hindrance because 2-methoxynaphtha-
lene, which is more reactive but has a smaller steric
hindrance at the 1-position than 2-methylnaphthalene,
gave the coupling product in excellent regioselectivity
although 2-methylnaphthalene showed low regioselec-
tivity. Furthermore, 1,4- and 1,5-dimethylnaphthalene,
which are more reactive than 1-methylnaphthalene, gave
only trace amounts of coupling products resulting in the
recovery of unreacted substrates. Therefore, steric hin-
such as AlCl3,5 FeCl3,6 and SbCl3 are reported to be
7
effective oxidants for aromatic compounds that produce
biaryls through the formation of aromatic radical cations.
The latter reaction is known as the Scholl reaction.8
While the formation of biaryls is regarded as conclusive
evidence for the formation of aromatic radical cations as
† Osaka National Research Institute.
‡ Osaka Institute of Technology.
§ Research Institute of Innovative Technology for the Earth.
(1) (a) Todres, Z. V. Tetrahedron 1983, 41, 2771. (b) Schlesener, C.
J .; Kochi, J . K. J . Org. Chem. 1984, 49, 3142. (c) Schlesener, C. J .;
Amatore, C.; Kochi, J . K. J . Am. Chem. Soc. 1984, 106, 7472. (d)
Masnovi, J . M.; Kochi, J . K. J . Am. Chem. Soc. 1985, 107, 7880. (e)
Masnovi, J . M.; Sankararaman, S.; Kochi, J . K. J . Am. Chem. Soc.
1989, 111, 2263. (f) Kim, E. K.; Bockman, T. M.; Kochi, J . K. J . Chem.
Soc., Perkin Trans. 2 1992, 1879. (g) Kim, E. K.; Bockman, T. M.;
Kochi, J . K. J . Am. Chem. Soc. 1993, 115, 3091.
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P. J . Org. Chem. 1992, 57, 1917. (b) Smrcˇina, M.; Pola´kova´, J .;
Vyskocˇil, S.; Kocˇovsky´, P. J . Org. Chem. 1993, 58, 4534. (c) Smrcˇina,
M.; Vyskocˇil, Sˇ.; Ma´ca, B.; Pola´sˇek, M.; Claxton, T. A.; Abbott, A. P.;
Kocˇovsky´, P. J . Org. Chem. 1994, 59, 2156.
(3) McKillop, A.; Turrell, A. G.; Young, D. W.; Taylor, E. C. J . Am.
Chem. Soc. 1980, 102, 6504.
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(5) (a) Kovacic, P.; Kyriakins, A. J . Am. Chem. Soc. 1963, 85, 454.
(b) Hsing, C.; J ones, M. B.; Kovacic, P. J . Polym. Sci., Polym. Chem.
Ed. 1981, 19, 973. (c) Hsing, C.; Kovacic, P.; Khoury, I. A. J . Polym.
Sci., Polym. Chem. Ed. 1983, 21, 457. (d) Brown, C. E.; Kovacic, P.;
Wilkie, C. A.; Cody, R. B., J r.; Kinsinger, J . A. J . Polym. Sci., Polym.
Lett. Ed. 1985, 23, 453. (e) Kovacic, P.; J ones, M. B. Chem. Rev. 1987,
87, 357. Recently, it has been proposed that AlCl3 does not act as an
oxidant (see ref 5f). (f) Smith, G. P.; Dworkin, A. S.; Pagni, R. M.;
Zingg, S. P. J . Am. Chem. Soc. 1989, 111, 525.
(6) Toda, F.; Tanaka, K.; Iwata, S. J . Org. Chem. 1989, 54, 3007.
(7) (a) Dworkin, A. S.; Poutsma, M. L.; Brynestad, J .; Brown, L. L.;
Gilpatrick, L. O.; Smith, G. P. J . Am. Chem. Soc. 1979, 101, 5299. (b)
Buchanan, A. C., III; Dworkin, A. S.; Brynestad, J .; Gilpatrick, L. O.;
Poutsma, M. L.; Smith, G. P. J . Am. Chem. Soc. 1979, 101, 5430. (c)
Buchanan, A. C., III; Livingston, R.; Smith, G. P. J . Phys. Chem. 1980,
84, 423. (d) Buchanan, A. C., III; Dworkin, A. S.; Smith, G. P. J . Am.
Chem. Soc. 1980, 102, 5262. (e) Buchanan, A. C., III; Dworkin, A. S.;
Smith, G. P. J . Org. Chem. 1981, 46, 471. (f) Buchanan, A. C., III;
Dworkin, A. S.; Smith, G. P. J . Org. Chem. 1982, 47, 603. (g)
Buchanan, A. C., III; Dworkin, A. S.; Smith, G. P. J . Am. Chem. Soc.
1983, 105, 2843. (h) Zingg, S. P.; Dworkin, A. S.; Sørlie, M.; Chapman,
D. M.; Buchanan, A. C., III; Smith, G. P. J . Electrochem. Soc. 1984,
131, 1602. (i) Buchanan, A. C., III; Chapman, D. M.; Smith, G. P. J .
Org. Chem. 1985, 50, 1702. (j) Dworkin, A. S.; Brown, L. L.; Buchanan,
A. C., III; Smith, G. P. Tetrahedron Lett. 1985, 26, 2727.
(9) Bosch, E.; Kochi, J . K. J . Org. Chem. 1994, 59, 5573.
(10) (a) Kim, E. K.; Kochi, J . K. J . Org. Chem. 1989, 54, 1692. (b)
Bosch, E.; Kochi, J . K. J . Org. Chem. 1994, 59, 3314.
(11) (a) Bandlish, B. K.; Shine, H. J . J . Org. Chem. 1977, 42, 561.
(b) Musker, W. K.; Wolford, T. L.; Roush, P. B. J . Am. Chem. Soc. 1978,
100, 6416. (c) Radner, F. J . Org. Chem. 1988, 53, 3548. (d) Kim, E.
K.; Kochi, J . K. J . Am. Chem. Soc. 1991, 113, 4962. (e) Kim, E. K.;
Kochi, J . K. J . Org. Chem. 1993, 58, 786. (f) Bosch, E.; Rathore, R.;
Kochi, J . K. J . Org. Chem. 1994, 59, 2529.
(12) Radner, F. J . Org. Chem. 1988, 53, 702.
(8) (a) Scholl, R.; Seer, C.; Weitzenbo¨ck, R. Ber. Dtsch. Chem. Ges.
1910, 43, 2202. (b) Olah, G. A. Friedel-Crafts and Related Reactions;
Wiley-Interscience: New York, 1964; Vol. II, p 979. The Scholl reaction
using SbF5 is discussed in the Supporting Information.
(13) Eberson, L.; Radner, F. Acc. Chem. Res. 1987, 20, 53.
(14) The influence of solvents on the coupling reaction is discussed
in the Supporting Information.
(15) In the absence of NaNO2, no reaction was observed.
0022-3263/96/1961-0788$12.00/0 © 1996 American Chemical Society

Notes
J . Org. Chem., Vol. 61, No. 2, 1996 789
Ta ble 1. Cou p lin g Rea ction of Na p h th a len e Der iva tivesi
a
* Unreacted substrate was recovered. Isomer ratio of 2,2′-dimethyl-1,1′-binaphthyl:2,3′-dimethyl-1,1′-binaphthyl:other isomers. b Isomer
ratio of 2,3′-diethyl-1,1′-binaphthyl:2,2′-diethyl-1,1′-binaphthyl:other isomers. c Isomer ratio of 3,3′,4,4′-tetramethyl-1,1′-binaphthyl:other
d
isomers. Isomer ratio of 4,4′,7,7′-tetramethyl-1,1′-binaphthyl:other isomers. e Isomer ratio of 2,3,6′,7′-tetramethyl-1,1′-binaphthyl:2,2′,3,3′-
tetramethyl-1,1′-binaphthyl. f Isomer ratio of 2,2′,6,6′-tetramethyl-1,1′-binaphthyl:2,3′,6,7′-tetramethyl-1,1′-binaphthyl:other isomers.
g
h
i
Isomer ratio of 2,2′,7,7′-tetramethyl-1,1′-binaphthyl:other isomers. Isomer ratio of 4,4′-dimethoxy-1,1′-binaphthyl:other isomers. The
reactions were carried out using 0.5 mmol of NaNO2, 10 mmol of CF3SO3H, and 5 mmol of substrate in air for 1 h.

790 J . Org. Chem., Vol. 61, No. 2, 1996
Notes
Ta ble 3. Cou p lin g Rea ction of 1-Meth yln a p h th a len ea
Ta ble 2. Rea ction Usin g Nitr o-1-m eth yln a p h th a len ea
substrate composition
1-methylnaphthalene:
nitro-1-methylnaphthalene
products yield (%)
CF3SO3H
(mmol) atmosphere
entry oxidant
1
2
3
4
5
products yield (%)
1
2
3
4
5
6
NaNO2
NaNO2
NOBF4
NOBF4
NO2BF4
NO2SbF6
10
10
10
0
10
10
air
N2
air
air
air
air
0
0
0
5
0
0
0
0
0
0
97
15
90
0.8
86
55
1.5
0
0
0
0
0
0
0
0
0
0
(mmol)
1
2
3
4
5
0:0.7
0.7:0.7
0.7:0
93
46
0
0
0
0
0
19
15
0
1.1
1.9
1.4
4.8
1.9
0.7
2.3
a
0
The reactions were carried out using 1 mmol of NaNO2, 10
mmol of CF3SO3H, and 50 mL of CH3CN at 0 °C in air for 1 h.
The yield was determined on the basis of the total amounts of
substrates.
a
The reactions were carried out using 0.5 mmol of an oxidant,
5 mmol of 1-methylnaphthalene, and 50 mL of CH3CN at 0 °C for
1 h.
the 1 radical cation was not formed by NO+. Next, the
reaction using equimolar amounts of 1-methylnaphtha-
lene and 1 was carried out to give the same amount of 1
as the former reaction using only 1, but the reaction using
only 1-methylnaphthalene did not give 1 at all. These
results show that 1 is inert under these conditions, and
4 and 5 were formed through the nitration of 3 with NO2
or NO2. Therefore, the formation path of the products
can be described as follows.
drance is obviously an important factor for controlling
the yield and regioselectivity during this reaction.
A
similar result is reported for the iodination reaction of
aromatic compounds using ICI.16
F or m a tion P a th of P r od u cts. In the reaction of
1-methylnaphthalene with NaNO2 in the presence of
CF3SO3H, five products, nitro-1-methylnaphthalene (1),
dinitro-1-methylnaphthalene (2), 4,4′-dimethyl-1,1′-bi-
naphthyl (3), nitro-4,4′-dimethyl-1,1′-binaphthyl (4), and
dinitro-4,4′-dimethyl-1,1′-binaphthyl (5) were formed, and
the product composition was dependent on the combina-
tion of reagents. When the amount of NaNO2 was small,
the product 3 was produced mainly in the presence of
CF3SO3H. With an increasing amount of NaNO2, the
nitration proceeded to give 1, 2, 4, and 5. On the other
hand, an increase in the CF3SO3H amount caused the
formation of 3, 4, and 5. However, no nitroso products
were obtained, which shows that NO+ acts only as an
oxidant for 1-methylnaphthalene. The identified isomers
of 1 were 2-nitro-, 3-nitro-, 4-nitro-, 5-nitro, and 8-nitro-
1-methylnaphthalene. However, in the case of 4, only
one isomer, 2-nitro-4,4′-dimethyl-1,1′-binaphthyl, was
identified because of the difficulty in separation. The
main isomers of 1 and 4 were 4-nitro-1-methylnaphtha-
lene (about 60% in ratio) and 2-nitro-4,4′-dimethyl-1,1′-
binaphthyl (about 80% in ratio), respectively. Isomers
of 2 and 5 were not identified because of their difficulty
in separation. Products 1 and 3 were clearly formed
through the coupling reaction of the 1-methylnaphtha-
lene radical cation with NO217 or 1-methylnaphthalene,10
respectively. On the other hand, there are two plausible
reaction paths for 2, 4, and 5. For 2, the plausible
+
Ca ta lytic Cycle of NO+. In order to investigate the
catalytic cycle of NO+, the reactions of 1-methylnaph-
thalene were carried out using NaNO2 with CF3SO3H
under different conditions and using NOBF4, NO2BF4,
or NO2SbF6 instead of NaNO2. The results are tabulated
in Table 3. The coupling reaction of 1-methylnaphtha-
lene using NaNO2 with CF3SO3H at 0 °C in air gave 3
and 4 in 97% and 1.5% yields, respectively (entry 1).
However, when the reaction using the same amounts of
materials was carried out under a N2 atmosphere (entry
2), the yield of 3 decreased from 97% to 15%, and 4 was
not formed. Therefore, the oxidation of NO with O2 to
form NO2 after the electron transfer of NO+ with 1-
methylnaphthalene is one step of the cycle. Next, the
reactions using NOBF4 were conducted in the presence
or absence of CF3SO3H. In the presence of CF3SO3H
(entry 3), 3 was obtained in excellent yield similar to the
reaction using NaNO2 (entry 1). However, in the absence
of CF3SO3H, only a small amount of 1-methylnaphtha-
lene was converted to 1 as the main product and 3, and
unreacted substrate was recovered (entry 4). These
results show that CF3SO3H protonates NO2, N2O4, and
+
reaction paths are the nitration of 1 with NO2 and the
coupling reaction of the 1 radical cation with NO2. For
4 and 5, the paths include the nitration (the electrophilic
substitution by NO2+ and the coupling reaction by NO2)
of 3 or 4 and the coupling reaction of the 1-methylnaph-
thalene radical cation or the 1 radical cation with 1,
respectively. In order to investigate the formation path
of the products, the reactions were carried out using a
mixture of 1-methylnaphthalene and 1, and the results
are summarized in Table 2. When the reaction was
conducted using only 1, no reaction occurred. Therefore,
2 was produced by the nitration of 1 with NO2+ because
(16) Hubig, S. M.; J ung, W.; Kochi, J . K. J . Org. Chem. 1994, 59,
6233.
(17) Eberson, L.; Radner, F. Acta Chem. Scand. 1986, 40, 71. When
the reaction of 1-methylnaphthalene (5 mmol) with NOBF4 (5 mmol)
was carried out in the absence of CF3SO3H at -45 °C in CH3CN (25
mL) with CH2Cl2 (25 mL), five isomers of nitro-1-methylnaphthalene,
2-nitro-, 3-nitro-, 4-nitro-, 5-nitro-, and 8-nitro-1-methylnaphthalene,
were identified, and the isomer distribution was 4:1:84:8:3. This isomer
distribution shows fairly good agreement with the results of the
coupling nitration of 1-methylnaphthalene radical cation salt with NO2
at -70 °C, 8:0:88:1:3 (see ref 15). Therefore, we concluded that the
nitration is a radical reaction.
NO+NO3 exactly to reproduce NO+ with the formation
-

Notes
J . Org. Chem., Vol. 61, No. 2, 1996 791
+ 18
of an equal amount of NO2
.
Recently, it has been
+
proposed that NO2 has the ability to function not only
as an electrophile but also as an oxidant, which oxidizes
NO to form NO+.19 In order to study whether NO2+ acts
as the oxidant of NO to form NO+ or as an electrophile
to form 1, the reaction was conducted using NO2BF4 and
NO2SbF6, which is known to always contain a small
amount of NO+ as an impurity, under the same condi-
tions in the presence of CF3SO3H (entries 5 and 6).
Similar to the reaction using NOBF4 (entry 3), 3 was
formed mainly, but the formation of 1 was observed.20
+
These results clearly show that NO2 acted as the
electrophile under the conditions when the NO concen-
tration was low, and the formation of 1 was not observed
when NaNO2 and NOBF4 were used in the presence of
+
CF3SO3H. Therefore, it seems that NO2 acts as the
oxidant of NO to produce NO+ rather than as an
electrophile to form 1 in the NaNO2-CF3SO3H system.
These results suggest the following catalytic cycle of
NO+.21
F igu r e 1. Coupling reaction of 1-methylnaphthalene using
5 mmol of NaNO2. The reactions were carried out using 5
mmol of 1-methylnaphthalene at 0 °C in air for 1 h. The
symbols 0, O, and b represent the yields of 1, 3, and 4,
respectively, and 2 and 5 were not formed under these
conditions.
NaNO2 + 2CF3SO3H f
SO3H to investigate the influence of CF3SO3H on the
nitration. The results are represented in Figure 1. The
yield of 1 decreased with an increasing amount of CF3-
SO3H. On the contrary, the yield of 4 increased with an
increase in CF3SO3H. This result reveals that CF3SO3H
has the ability to inhibit the nitration of 1-methylnaph-
thalene with NO2.22 The ability of CF3SO3H to inhibit
the nitration seems to stem from the ability to protonate
NO2 (N2O4 and NO+NO3-) before the coupling reaction
of NO2 with the 1-methylnaphthalene radical cation.21
In order to clarify this deduction, the reactions of 1-meth-
ylnaphthalene were conducted using several acids such
as FSO3H, CF3SO3H, and H2SO4 under the same condi-
tions, and the influence of acid strength on the ability to
inhibit the nitration was studied. The order of acid
strength of these acids is well-known as FSO3H > CF3-
SO3H > H2SO4. The results are shown in Table 4. The
yield order of coupling products (the sum of 3, 4, and 5)
was consistent with the acid strength order. This result
evidently shows that acids have two roles in this reaction,
which are the production of NO+ from NaNO2 and the
protonation of the formed NO2 (N2O4 and NO+NO3-) to
CF3SO3NO + CF3SO3Na + H2O
2‚NO + O2 f 2‚NO2
-
2‚NO2 h N2O4 h NO+NO3
NO+NO3- + 2CF3SO3H f
CF3SO3NO + CF3SO3NO2 + H2O
‚NO + CF3SO3NO2 f CF3SO3NO + ‚NO2
Role of Acid . In the NaNO2-CF3SO3H system, the
nitration of 1-methylnaphthalene was almost completely
inhibited when NaNO2 was used in a catalytic amount.
Therefore, equimolar amounts of NaNO2 and 1-methyl-
naphthalene were used with various amounts of CF3-
(18) (a) Boughriet, A.; Wartel, M. J . Chem. Soc., Chem. Commun.
1989, 809. (b) Bosch, E.; Rathore, R.; Kochi, J . K. J . Org. Chem. 1994,
59, 2529. (c) Bosch, E.; Kochi, J . K. J . Org. Chem. 1994, 59, 3314. (d)
Bosch, E.; Kochi, J . K. J . Org. Chem. 1995, 60, 3172. It is reported
that N2O4 which is in the equilibrium with NO2 dissociates to NO+NO3
-
in a solvent (see ref 16). In the presence of a strong acid such as CF3-
-
+
SO3H, NO3 is evidently converted to NO2 and H2O.
(21) The catalytic cycle in ref 13 is significantly different from our
proposal and is shown as follows.
(19) (a) Morrison, J . D.; Stanney, K.; Tedder, J . M. J . Chem. Soc.,
Perkin Trans. 2 1981, 967. (b) Clemens, A. H.; Ridd, J . H.; Sandall, J .
P. B. J . Chem. Soc., Perkin Trans. 2 1984, 1659. (c) Clemens, A. H.;
Ridd, J . H.; Sandall, J . P. B. J . Chem. Soc., Perkin Trans. 2, 1984,
1667. (d) Clemens, A. H.; Helsby, P.; Ridd, J . H.; Al-Omran, F.;
Sandall, J . P. B. J . Chem. Soc., Perkin Trans. 2 1985, 1217. (e) Lee,
K. Y.; Kuchycˇan, D. J .; Kochi, J . K. Inorg. Chem. 1990, 29, 4196. (f)
Lee, K. Y.; Amatore, C.; Kochi, J . K. J . Phys. Chem. 1991, 95, 1285.
(g) Eberson, L.; Gonzalez-Luque, R.; Lorentzon, J .; Merchan, M.; Roos,
B. O. J . Am. Chem. Soc. 1993, 115, 2898.
2ArH + 2NO+ f ArAr + 2NO + 2H+
2NO + 2H+ + 0.5O2 f 2NO+ + H2O
NO + NO2 + 2H+ f 2NO+ + H2O
Concerning the catalytic cycle of NO+, it is necessary to explain the
inhibition of the nitration by superacids, namely, the role of superacids
as NO2 scavengers. However, in ref 13, the role of acids is only to
produce NO+, and there is no description about the role of acids in
inhibiting the nitration. Therefore, we proposed that superacids can
act as NO2 scavengers by the protonation of N2O4 and NO+NO3-, not
NO2. The important concept is that O2 oxidizes two NO to give two
(20) (a) Eberson, L.; Radner, F. Acta Chem. Scand. 1984, 38, 861.
(b) Barnett, J . W.; Moodie, R. B.; Schofield, K.; Taylor, P. G.; Weston,
J . B. J . Chem. Soc., Perkin Trans. 2 1979, 747. (c) Roberts, R. M. G.;
Sadri, A. R. Tetrahedron 1983, 39, 137. (d) Tanaka, M.; Fujiwara, M.;
Ando, H. J . Org. Chem. 1995, 60, 2106. (e) Eberson, L.; Hartshorn,
M. P.; Radner, F. Acta Chem. Scand. 1994, 48, 937. The results are
very interesting because both yields of 1 (entries 5 and 6) were
significantly less than with NOBF4 (entry 4). To explain these results,
there are two plausible interpretations, the oxidation of 1-methyl-
naphthalene by NO2+ to produce radical cations and the inhibition of
NO2+ attack to 1-methylnaphthalene by the protonation. The former
has been studied widely, but is still controversial (see refs 12, 15, and
18a). The latter is derived from the fact that the protonation inhibits
electrophilic substitutions (see ref 18b-d) and means that NO2+ attack
may be inhibited more strongly than NO+ attack to 1-methylnaph-
thalene by the protonation; namely, NO+ reaction proceeds as the main
-
NO2; therefore, the NO2 produced by O2 may exist as N2O4 or NO+NO3+
first, and then, N2O4 and NO+NO3 are converted to NO+ and NO2
-
by superacids before the coupling reaction of the radical cation with
NO2 occurs to give nitro compounds.
(22) The catalytic cycle of NO+ shows that the concentration of NO2
in the reaction systems is dependent not only on the superacid
concentration (or the acid strength of superacids) but also on the
reaction time. According to the catalytic cycle, the concentration of
NO2 in the presence of superacids is low at the initial stage of the
reaction and increases with the progress of the reaction by the
+
formation of NO2 from NO2
. Therefore, it is difficult to inhibit the
reaction because NO2 and NO+ reactions seem to proceed through
inner- and outer-sphere reactions, respectively (see refs 12, 15, and
18a,e). We are now studying this problem using superacids.
nitration of produced binaphthyl derivatives by the addition of super-
acids because radical cations of binaphthyl derivatives are a secondary
product.
+

792 J . Org. Chem., Vol. 61, No. 2, 1996
Notes
Ta ble 4. In flu en ce of Acid Str en gth a
sary to more preferentially produce binaphthyl deriva-
tives than nitro compounds.
products yield (%)
acid
1
2
3
4
5
Exp er im en ta l Section
FSO3H
CF3SO3H
H2SO4
23
48
54
0
0
8.3
2.1
0
1.1
64
39
1.6
0
0
0
All reagents were of the highest available purity and were
used without further purification. Dry CH3CN was used when
NOBF4, NO2BF4, and NO2SbF6 were used. The product yields
were determined with GC by the internal standard method
(experimental error ) (5%). Nitrobenzene was used as an
internal standard, and the separated products were used for the
yield determination. The product structures were identified by
NMR (1H-, 13C-NMR, COSY, NOESY, CHSHF, and COLOC) and
mass analysis after isolation by recrystallization or GPC.
Cou p lin g Rea ction P r oced u r es Usin g Na NO2, NOBF 4,
NO2BF 4, a n d NO2SbF 6. The required amounts of oxidant and
acid were placed in a three-necked flask (300 mL) containing
50 mL of solvent (40 mL for solid substrates such as naphtha-
lene, 1,4-, 1,5-, 1,8-, 2,3-, 2,6-, and 2,7-dimethylnaphthalene,
2-methoxynaphthalene, and 2-naphthol), and a substrate was
added to the mixture with vigorous stirring in air under
temperature control. When the substrate was a solid, the
solution of the substrate dissolved in a suitable solvent was
added to a mixture (10 mL of CH3CN for naphthalene, and 1,4-,
1,8-, and 2,7-dimethylnaphthalene, 20 mL of CH3CN for 2,3-
dimethylnaphthalene, a mixture of CH3CN (5 mL) and CH2Cl2
(5 mL) for 2-methoxynaphthalene and 2-naphthol, and a mixture
of CH3CN (10 mL) and CH2Cl2 (10 mL) for 1,5- and 2,6-
dimethylnaphthalene). After 1 h, the reaction mixture was
poured into ice water and extracted with CHCl3. The product
yields and structures were determined according to the general
procedures.
a
The reactions were carried out using 5 mmol of NaNO2, 15
mmol of acid, 5 mmol of 1-methylnaphthalene, and 50 mL of
CH3CN at 0 °C in air for 1 h.
inhibit the nitration and to produce NO+ and NO2
Strong acids give the formation of biaryls an advantage
over the formation of nitro compounds.
.
+
Ack n ow led gm en t. We thank Dr. Yoshiko Naka-
hara (Research Institute of Innovative Technology for
the Earth) and Professor Toshiyuki Shono (Department
of Applied Chemistry, Faculty of Engineering, Osaka
Institute of Technology) for their assistance with our
work.
Con clu sion s
It was found that the coupling reaction of naphthalene
derivatives using NaNO2 with CF3SO3H in CH3CN
catalytically gave the corresponding 1,1′-binaphthyl de-
rivatives in air. The reaction is strongly influenced by
steric hindrance; therefore, high regioselectivity was
observed in some substrates. The acids have two roles
in the reaction, which are the production of NO+ and the
inhibition of the nitration by the protonation of NO2
(N2O4 and NO+NO3-). Therefore, strong acids are neces-
Su p p or tin g In for m a tion Ava ila ble: Discussion of the
influence of solvents on the coupling reaction and the Scholl
reaction using SbF5 (6 pages). This material is contained in
libraries on microfiche, immediately follows this article in the
microfilm version of the journal, and can be ordered from the
ACS; see any current masthead page for ordering information.
J O950814B