Herein, we report a simple and convenient method for
the conversion of arylboronic acid to nitroarenes using
Bi(NO3)3 5H2O/K2S2O8 asthe nitratingagent(Scheme 1).
Table 2. ipso-Nitration of Phenylboronic Acid with Different
Solvents
3
Bismuth reagents have been extensively used in synthetic
chemistry due to their low toxicity and ready availability.19
Aromatic nitro compounds possessing a variety of elec-
tron-donating and -withdrawing functional groups can be
synthesized following this protocol. Moreover, the present
method showed that some heterocylic nitro compounds
could also be generated in good yield.
GC
We began our ipso-nitration protocol by studying the
reaction ofphenylboronic acid withdifferentcommercially
available nitrate sources (Table 1).20
temp
yield
(%)
entry
solvent
toluene
(°C)
1
80
100
80
100
62
100
90
70
70
51
15
15
1
2
toluene
3
o-xylene
4
benzene
80
Table 1. Effect of Different Nitrate Salts in the ipso-Nitration of
Phenylboronic Acid
5
trifluorotoluene
ClCH2CH2Cl
cyclohexane
DMSO
80
6
70
7
60
8
50
9
acetone
40
10
11
DMF
110
90
dioxane
1
GC
Nonpolar solvents, including toluene and o-xylene, were
foundtogivethebest results at80°C (Table2, entries 1 and
3, respectively). However, temperatures higher than 80 °C
led to lower conversion due to increased protodeborona-
tion reactions.20 While trifluorotoluene and benzene were
considerably good solvents, giving 70% and 90% yields of
the desired nitro product, respectively, ipso-nitration was
not observed with dioxane and DMF. Other polar solvents
such as acetone and DMSO produced little nitro product.
The choice of solvent thus has been restricted to relatively
nonpolar hydrocarbon solvents, among which toluene was
chosen as the most suitable solvent. While studying the
substrate scope we have realized that benzene can also be
used as a useful solvent in some ipso-nitration reactions.
Having fully optimized reaction conditions in hand, we next
temp
yield
(%)
entry
nitrate source
(°C)
1
2
3
4
5
6
7
8
9
10
Bi(NO3)3 5H2O
80
70
100
94
62
51
38
33
1
3
Bi(NO3)3 5H2O
3
AgNO3
100
100
100
100
80
Cd(NO3)2
Mg(NO3)2
NH4Ce(NO3)4
Pb(NO3)3
NaNO3
100
80
1
NaNO2
1
AgNO2
80
1
Using Cd(NO3)2 at 100 °C, nitrobenzene was generated
in 51% yield after 12 h, while a relatively better result was
obtained with AgNO3 under the same reaction conditions
(Table 1). Subsequently, the best result was achieved with
1 mmol of Bi(NO3)3 5H2O at 80 °C (Table 1, entry 1).
Later, it was found that an increase in the amount of
Bi(NO3)3 5H2O had some detrimental effect, resulting in a
lower yield of the nitro product. Other nitrate sources such
as NaNO3 or Pb(NO3)2 and nitrite sources such as NaNO2
or AgNO2 failed to give the nitro product.
set out to explore the substrate scope of the Bi(NO3)3 5H2O/
3
K2S2O8 catalyzed transformation of arylboronic acids to
nitroaromatics. With various alkyl and aryl substituted ar-
ylboronic acids, nitrated products were obtained in good to
excellent yields (Scheme 2, 2bꢀ2d, 2gꢀ2i). Sterically demand-
ing arylboronic acids with 2-methyl (2g) and 2,6-dimethyl (2h)
substituents resulted in the desired nitro product in excellent
yields. ortho-Phenoxy (2e) and ortho-benzyloxy (2f) substi-
tuted nitroarenes were also synthesized in 83% and 81%
yields, respectively, following the standard protocol. A recent
report described the generation of cyclized dibenzo[b,d]furan
derivatives from 2-aryloxyarylboronic acids by using AgNO3/
3
3
(13) Prakash, G. K. S.; Panja, C.; Mathew, T.; Surampudi, V.;
Petasis, N. A.; Olah, G. A. Org. Lett. 2004, 6, 2205.
(14) Prakash, G. K. S.; Mathew, T. Angew. Chem., Int. Ed. 2010,
1726.
(15) Saito, S.; Koizumi, Y. Tetrahedron Lett. 2005, 46, 4715.
(16) Wu, X. F.; Schranck, J.; Neumann, H.; Beller, M. Chem.
Commun. 2011, 47, 12462.
(17) Yang, H. J.; Li, Y.; Jiang, M.; Wang, J. M.; Fu, H. Chem.;Eur.
J. 2011, 17, 5652.
(18) Fors, B. P.; Buchwald, S. L. J. Am. Chem. Soc. 2009, 131, 12898.
(19) Leonard, N. M.; Wieland, L. C.; Mohan, R. S. Tetrahedron
2002, 58, 8373.
(21) We have observed the solvent nitration product in a few cases.
For example, PhCH2NO2 was isolated in ∼10% yield from toluene.
Toluene as substrate/solvent (without arylboronic acid) resulted in the
formation of PhCH2NO2 and PhCO2H and other solvent oxidized
products. Benzene as a substrate/solvent (without arylboronic acid)
gave nitrobenzene in 38% yield. However in the presence of arylboronic
acid, only 5ꢀ10% of nitrobenzene formation was detected.
(22) Lockner, J. W.; Dixon, D. D.; Risgaard, R.; Baran, P. S. Org.
Lett. 2011, 13, 5628.
(20) See Supporting Information.
Org. Lett., Vol. 14, No. 7, 2012
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