One-pot synthesis of N-substituted diaza[12]annulenes

Article abstract of DOI:10.1021/ol061585q

(Chemical Equation Presented) N-Substituted diaza[12]annulenes are obtained by one -pot reaction of n-(2,4-dinitrophenyl)pyridinium chloride with amines in moderate to high yields. The ¹H NMR spectrum reveals that diamagnetic ring current is generated in the diaza[12]annulene ring. The N-substituted diaza[12]annulenes are electrochemically active in solution.

Full text of DOI:10.1021/ol061585q

ORGANIC
LETTERS
2006
Vol. 8, No. 19
4279-4281
One-Pot Synthesis of N-Substituted
Diaza[12]annulenes
Isao Yamaguchi,* Yoshiaki Gobara, and Moriyuki Sato
Department of Material Science, Faculty of Science and Engineering, Shimane
UniVersity, 1060 Nishikawatsu, Matsue 690-8504, Japan
iyamaguchi@riko.shimane-u.ac.jp
Received June 28, 2006
The authors have retracted this paper on November 15, 2007 (Org. Lett. 2007, 24, 5139) due to uncertainties
regarding what products are formed in the reaction described.
ABSTRACT
N-Substituted diaza[12]annulenes are obtained by one -pot reaction of N-(2,4-dinitrophenyl)pyridinium chloride with amines in moderate to
high yields. The 1H NMR spectrum reveals that diamagnetic ring current is generated in the diaza[12]annulene ring. The N-substituted diaza-
[12]annulenes are electrochemically active in solution.
Annulenes have attracted much attention since the first report
on [8]annulene in 1911.1 Many efforts have been devoted
to probing the (anti)aromaticity of [4n]annulenes by using
NMR spectroscopy and computational methods.2-4 The addi-
tion of π-electrons to the [4n]annulenes that are antiaromatic
in the Hu¨ckel sense has been carried out to alter their aroma-
ticity and magnetic properties.5-8 Among the [4n]annulenes,
studies on [12]annulenes and hetero[12]annulenes are very
limited due to their decreased thermal stability.6,9-11 Steven-
son reported that [12]annulenes show diamagnetic properties.10a
To our knowledge, the subtraction of two π-electrons from
a [4n]annulene to provide a dicationic [4n]annulene contain-
ing (4n - 2)π electrons has no precedent. The aromaticity
and chemical properties of dicationic [4n]annulenes and
hetero[4n]annulenes remain elusive.
The introduction of a substituent on the nitrogen atoms
of a diaza[12]annulene will give a dicationic species. It is
known that the thermal and electronic properties of N-
substituted aza[4n + 1]annulenes (n ) 2, 3, and 4) vary
depending on the N-substituent.12-14 Investigation of the
aromaticity and chemical properties of the N-substituted
diaza[12]annulenes will provide new information about
hetero[4n]annulenes. However, there is only one report on
such a diaza[12]annulene,11 and its N-substitution reaction
to generate a dicationic species has not yet been performed.
Herein, we report the one-pot synthesis of N-substituted
diaza[12]annulenes and an investigation of their aromaticity
and their structural, optical, and electrochemical properties.
A plausible reaction pathway is also reported.
(1) Willstater, R.; Waser, E. Ber. Dtsch. Chem. Ges 1911, 44, 3423.
(2) Kennedy, R. D.; Lioyd, D.; McNab, H. J. Chem. Soc., Perkin Trans.
1 2002, 1601.
(3) Mitchell, R. H. Chem. ReV. 2001, 101, 1301.
(4) Sondheimer, F. Acc. Chem. Res. 1972, 5, 81.
(5) (a) Strauss, H. K.; Katz, T. J.; Fraenkel, G. K. J. Am. Chem. Soc.
1963, 85, 2360. (b) Cox, R. H.; Harrison, L. W.; Austin, W. K., Jr. J. Phys.
Chem. 1973, 77, 200.
(6) Oth, J. F. M.; Schro¨der, G. J. Chem. Soc. B 1971, 904.
(7) (a) Oth, J. F. M.; Baumann, H.; Gilles, J. M.; Schro¨der, G. J. Am.
Chem. Soc. 1972, 94, 3498. (b) Baumann, H.; Oth, J. F. M. HelV. Chim.
Acta 1980, 63, 618.
(8) Oth, J. F. M.; Woo, E. P.; Sondheimer, F. J. Am. Chem. Soc. 1973,
95, 7337.
(9) (a) Oth, J. F. M.; Gilles, J.-M.; Schro¨der, G. Tetrahedron Lett. 1970,
61. (b) Oth, J. F. M.; Ro¨ttele, H.; Schro¨der, G. Tetrahedron Lett. 1970, 67.
(10) (a) Stevenson, G. R.; Concepcion, R.; Reiter, R. C. J. Org. Chem.
1983, 48, 2777. (b) Gard, M. N.; Reiter, R. C.; Stevenson, C. D. Org. Lett.
2004, 6, 393.
N-Substituted diaza[12]annulenes (3) were obtained by a
2:2 reaction of N-(2,4-dinitrophenyl)pyridinium chloride (1)
with substituted amines15 (2) in 40-83% yields (Scheme 1).
(12) Anastassiou, A. G.; Eachus, S. W.; Gellura, R. P.; Gelbrian, J. H.
Chem. Commun. 1970, 1133.
(13) (a) Anastassiou, A. G.; Reichmanis, E.; Elliott, R. L. Tetrahedron
Lett. 1973, 3805. (b) Anastassiou, A. G.; Elliott, R. L.; Reichmanis, E. J.
Am. Chem. Soc. 1974, 96, 7823.
(14) (a) Schro¨der, G.; Heil, G.; Ro¨ttle, H.; Oth, J. F. M. Angew. Chem.
1972, 84, 474. (b) Schro¨der, G.; Frank, G.; Ro¨ttle, H.; Oth, J. F. M. Angew.
Chem. 1974, 86, 237. (c) Ro¨ttle, H.; Heil, G.; Schro¨der, G. Chem. Ber.
1978, 111, 84.
(11) Bindra, A. P.; Elix, J. A. Tetrahedron 1970, 26, 3749.
10.1021/ol061585q CCC: $37.00
© 2006 American Chemical Society
Published on Web 08/16/2006

Scheme 1. Reaction of N-(2,4-Dinitrophenyl)pyridinium
Chloride (1) with Amine (2)
The results of these reactions are summarized in Table 1.
Reaction of 1 with 4-haloaniline (entries 4-7) gave a mixture
Figure 1. 1H NMR spectrum of 3a in DMSO-d6 at 20 °C.
1
Table 1. Results of Reaction of N-(2,4-
Dinitrophenyl)pyridinium Chloride (1) with Amines (2)
The H NMR peak positions and J values corresponding
to the hydrogen atoms of the diaza[12]annulene ring of 3a-g
were essentially the same, independent of the structure of
the N-substituent. The appearance of the 1H NMR peaks of
the diaza[12]annulene ring at lower magnetic field positions
by about 2-3 ppm compared with those of the outer
hydrogens of the [12]annulenes9b and hetero[12]annulenes11,19
has been ascribed to the generation of diamagnetic ring
currents in the diaza[12]annulene ring. Such a downfield shift
yield, %
entrya
2
Ar
3b
4c
1
2
3
4
5
6
7
2a
2b
2c
2d
2e
2f
2,5-Me-C6H3
p-MeO-C6H4
p-F-C6H4
p-Cl-C6H4
p-Br-C6H4
p-I-C6H4
3a, 40
3b, 83
3c, 62
3d, 73
3e, 76
3f, 46
3g, 40
0
0
0
4d, 6
4e, 3
4f, 3
0
1
of the H NMR peak induced by diamagnetic ring current
2g
n-hexyl
was also observed in the [12]annulene anion.6
The diaza[12]annulenes give rise to two absorption bands
in the ranges of 255-284 and 351-396 nm, and their relative
intensities vary depending on the structures of the N-
substituents, as summarized in Table 2. It is reported that
a Ethanol solution of 1 and 2 in a 1:2 molar ratio was refluxed for 12 h
1
under nitrogen. b Isolated yield. c Estimated from H NMR spectrum of a
mixture of 3 and 4.
of N-halophenyl diaza[12]annulene dichloride and N-halophe-
nylpenta-2,4-dienylidene-1-N-halophenylinium chloride (4).16
The diaza[12]annulenes obtained were soluble in water and
polar aprotic solvents such as N,N-dimethylformamide,
dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidinone.
Table 2. Absorption and Electrochemical Oxidation Potential
Data of Diaza[12]annulene Dichloride (3)
absorption,a nm
Ea,c V
(vs Ag+/Ag)
1
entry
3
(log ꢀ, M-1 cm-1
)
The structures of 3 and 4 were confirmed by FAB-MS, H
and 13C NMR spectroscopy, and elemental analysis.
1
2
3
4
5
6
7
3a
3b
3c
3d
3e
3f
255 (3.95), 351 (2.85)
0.79
0.77
1.15
1.07
1.00
0.99
0.73
1
264 (5.56), 333 (5.18),b 396 (4.51)
268 (4.53), 297 (3.88)
Figure 1 depicts the H NMR spectrum of 3a in DMSO-
d6. Peaks at δ 9.29, 8.83, and 8.33 are assigned to Ha, Hc,
and Hb of the diaza[12]annulene ring, respectively. Observa-
tion of these three signals of the diaza[12]annulene ring in
a 2:1:2 integral ratio suggests that the diaza[12]annulene ring
has a C2-symmetric conformation. As judged from the
coupling constants, JH -H ) 5.9 Hz and JH - H ) 6.6 Hz,
266 (4.79), 365 (3.92)
284 (4.01)
269 (4.51), 292 (4.56), 369 (4.05)
258 (4.17), 336 (3.58), 395 (3.31)
3g
a In EtOH. b Shoulder peak. c In DMSO solution including Et4NBF4 (0.1
M). Sweep rate was 50 mV s-1
a
b
b
c
.
the diaza[12]annulene ring may form an all-cis geometrical
structure at 20 °C, as shown in Figure 1. 13C NMR data also
support this structure.17 A previous report predicted the all-
cis structure to be the most stable of the six geometries of
[12]annulene isomers.18
N-substituted aza[9]annulenes exhibit two absorption bands
and their intensities are affected by the structures of the
N-substituents.12 Diaza[12]annulene 3b exhibited absorptions
at longer wavelengths than those exhibited by 3a, probably
(15) Reactions of 1 with 4-nitroaniline and with 4-aminoacetophenone
did not give both 3 and 4. A possible reason for the results is that low
basicity of the amines prevents nucleophilic addition to the pyridinium ring
of 1.
(16) It was reported that reaction of 1 with amine in a 1:1 molar ratio
gave N-arylpenta-2,4-dienylidene-1-N-arylinium chloride. See: Becher, J.
Synthesis 1980, 589.
(17) Three 13C NMR signals due to the diaza[12]annulene ring were
observed at δ 142.2, 146.1, and 142.0.
(18) Castro, C.; Karney, W. L.; Vu, C. M. H.; Burkhardt, S. E.; Valencia,
M. A. J. Org. Chem. 2005, 70, 3602.
(19) Holms, A. B.; Sondheimer, F. J. Am. Chem. Soc. 1970, 92, 5284.
4280
Org. Lett., Vol. 8, No. 19, 2006

Scheme 2. Possible Reaction Mechanism for N-Substituted Diaza[12]annulene Dichloride
due to the expansion of the π-conjugation system from the
Scheme 2 shows a plausible preparation mechanism for
the diaza[12]annulene dichloride (3) and N-arylpenta-2,4-
dienylidene-1-N-arylnium chloride (4), where nucleophilic
addition of amine to the pyridinium ring of 1 occurs first,
followed by ring-opening of the dihydropyridyl ring and
elimination of 2,4-dinitroaniline by reaction of the ring-
opening compound with 2 to provide 4 (path a). The reaction
of N-(2,4-dinitrophenyl)penta-2,4-dienylidene-1-N-arylinium
chloride with amine to give 4 has been reported.20 The 3:4
preparative ratios obtained by reaction of 1 with aromatic
amines depend on the basicity of the amine. These results
indicate that the nucleophilic addition of the NH group of 4
to the pyridinium ring of 1 is a crucial step for generation
of the diaza[12]annulene ring.
diaza[12]annulene ring to the 4-methoxyphenyl groups.
The steric effect of the methyl group at the 2-position of
the 2,4-dimethylphenyl ring of 3a may hinder the expansion
of the π-conjugation system. The absorption data often give
valuable information in predicting the planarity of the
annulene ring. The reported tetrabenzodiaza[12]annulene has
a nonplanar ring structure, and exhibits absorptions at 235
and 300 nm.11 The diaza[12]annulene ring of 3 seems to have
a more planar structure than that of tetrabenzodiaza[12]-
annulene, as judged from the absorption data.
Cyclic voltammetry measurements suggested that the
diaza[12]annulenes underwent electrochemical oxidation in
a DMSO solution including Et4NBF4. Figure 2 depicts CV
In summary, N-substituted diaza[12]annulenes were ob-
tained in moderate to high yields by the one-pot reaction of
N-(2,4-dinitrophenyl)pyridinium chloride with amines. The
1H NMR spectra of the products revealed that a diamagnetic
ring current was generated in the diaza[12]annulene ring.
Cyclic voltammetry analysis indicated that the diaza[12]-
annulenes were electrochemically active in solution. Diaza-
[12]annulenes with 4-halophenyl substituents would be a
useful starting material for functional compounds and
polymers. These approaches are under investigation in our
laboratory.
Acknowledgment. The authors wish to thank Dr. H.
Fukumoto (Tokyo Institute of Technology) for help with MS
measurements.
Figure 2. CV curves of 3a and 3g in a DMSO solution including
Et4NBF4 (0.1 M). Sweep rate was 50 mV s-1
.
Supporting Information Available: Experimental pro-
cedures and compound characterization data. This material
is available free of charge via the Internet at http://pubs.acs.org.
curves of 3a and 3g. As summarized in Table 2, the oxidation
potential is dependent on the N-substituent; 3g with electron-
donating n-hexyl substituents (entry 7) shows a peak at a
lower oxidation potential than the compounds with electron-
withdrawing substituents, 3c-f (entries 3-6).
OL061585Q
(20) Kavalek, J.; Lycka, A.; Machacek, V.; Sterba, V. Collect. Czech.
Chem. Commun. 1974, 39, 2056.
Org. Lett., Vol. 8, No. 19, 2006
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