The ionic introduction of an N1 unit to C60 and a unique rearrangement of aziridinofullerene

Article abstract of DOI:10.1039/b715348a

A new chloramine-based aziridination of C₆₀ and unique rearrangement of aziridinofullerene to azafulleroid is described. The ionic introduction of an N₁ unit to C₆₀via an addition-cyclization mechanism was first achieved under mild conditions; the combination of chloramine and MS4A resulted in the promising rearrangement of aziridinofullerene to azafulleroid, and the isomerization could be performed catalytically. The Royal Society of Chemistry.

Full text of DOI:10.1039/b715348a

Chemical Communications
www.rsc.org/chemcomm
Number 3 | 21 January 2008 | Pages 265–396
ISSN 1359-7345
COMMUNICATION
Satoshi Minakata, Ryoji Tsuruoka, Toshiki Nagamachi and Mitsuo Komatsu
The ionic introduction of an N1 unit to C60 and a unique rearrangement of
aziridinofullerene

COMMUNICATION
www.rsc.org/chemcomm | ChemComm
The ionic introduction of an N1 unit to C60 and a unique rearrangement
of aziridinofullerene{
Satoshi Minakata,* Ryoji Tsuruoka, Toshiki Nagamachi and Mitsuo Komatsu
Received (in Cambridge, UK) 5th October 2007, Accepted 6th November 2007
First published as an Advance Article on the web 13th November 2007
DOI: 10.1039/b715348a
a decrease in the yield of the monoadduct. Even though the
reaction proceeded at ambient temperature, the efficiency was
rather low compared to reflux conditions. The recovered and
reusable C60 (81%) was easily separable by silica gel column
chromatography. Two possible pathways—addition of a nitrene
species generated by the dechlorination of chloramine 1a or the
ionic addition–cyclization path shown in Scheme 1—should be
considered for the present aziridination of C60. Because it is known
that a triplet nitrene is generated from CT and AgNO3,10d the
system was employed in this reaction with C60, but no adduct was
formed. Although nitrene should not be generated from CT in the
absence of AgNO3, the treatment of C60 with 1a under an
atmosphere of oxygen gave the same result as that shown in
Scheme 1, indicating that the reaction did not involve radical
species. Moreover, the desired aziridinofullerene was not produced
at all in the water–toluene bilayer system. From these experiments,
the active species of the present reaction must be the anionic
nitrogen of CT. Therefore, the aziridination can be regarded as an
aza-version of the Bingel reaction.11
A new chloramine-based aziridination of C60 and unique
rearrangement of aziridinofullerene to azafulleroid is described.
The ionic introduction of an N1 unit to C60 via an addition–
cyclization mechanism was first achieved under mild condi-
tions; the combination of chloramine and MS4A resulted in the
promising rearrangement of aziridinofullerene to azafulleroid,
and the isomerization could be performed catalytically.
The development of
a basic and facile method for the
functionalization of C60 remains an important challenge because
of recent demands for carbon nanomaterials.1 The introduction of
N1 units to C60 with organic azides, leading to closed [6,6]-bridged
aziridinofullerenes2 and opened [5,6]-bridged azafulleroids,3 was
originally developed by Wudl et al.3a Since then, other examples of
aziridination using nitrenes4,5 or an iminoiodane under ultrasonic
irradiation6 have been reported. Aziridinofullerenes and azafuller-
oids are commonly formed via 1,3-dipolar cycloaddition, by the
addition of nitrenes, or through radical reactions. Isomerization of
the two compounds is performed by thermal treatment7 or
photoirradiation.3b,8 Selective formation of the two isomers,
involving N2 extrusion from triazorinofullerenes, can be controlled
by thermal or photochemical conditions.8a The aziridination of C60
is a powerful method for rendering the molecule functional;
azafulleroids, in particular, are key precursors for azafullerene
‘‘C59N’’ synthesis.9 However, some problems remain—namely,
most nitrogen sources are not commercially available and require
careful handling. Alternatively, our group has developed methods
for the aziridination of olefins10 using chloramine-T (CT) as an N1
source; however, these methods are ineffective for the formation of
aziridinofullerenes. This paper describes the first example of the
ionic aziridination of C60 with chloramines utilizing the electron-
acceptor nature of C60 via nucleophilic addition followed by
intramolecular cyclization. Addition of molecular sieves, 4A
(MS4A) to the reaction system induced the unique rearrangement
of aziridinofullerene to azafulleroid.
When optimizing the reaction conditions, the addition of MS4A
to the reaction system not only improved the efficiency of the
reaction but also produced opened, [5,6]-bridged azafulleroid 3a as
a main product (Table 1, entry 1 vs. 2). Since aziridinofullerene 2a
rearranged at 180 uC in ortho-dichlorobenzene for 5 h to give 3a in
58% yield, the effect of MS4A on the formation of 3a was readily
apparent. The result indicates that azafulleroid 3a was formed
under thermodynamic control and aziridinofullerene 2a was
selectively formed under kinetic control in the relatively mild
conditions.
The addition of CaCl2 in place of MS4A did not result in the
formation of any azafulleroid 3a, suggesting that MS4A does not
CT was first converted into its ammonium salt because of its
low solubility in toluene. The reaction of C60 with an equimolar
amount of ion-exchanged CT, 1a, in toluene under reflux for
10 min gave closed, [6,6]-bridged N-4-methylbenzenesulfonyl-
azirizinofullerene (2a) in 89% yield (Scheme 1). Increasing the
reaction time caused the formation of multi-CT adducts, leading to
Department of Applied Chemistry, Graduate School of Engineering,
Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871, Japan.
E-mail: minakata@chem.eng.osaka-u.ac.jp; Fax: +81 6-6879-7402
{ Electronic supplementary information (ESI) available: Procedure of
synthesis and experimental data for the products. See DOI: 10.1039/
b715348a
Scheme 1 Addition–cyclization of CT to C60.
Chem. Commun., 2008, 323–325 | 323
This journal is ß The Royal Society of Chemistry 2008

Table 1 Effects of MS4A on the formation of azafulleroids
Entry
Chloramine (equivalents)
Additive
Time/min
Yield (%)a,b
Ratio (3/2)
1
2
3
4
5
6
7
8
a
1a (1.0)
1a (1.0)
1a (1.0)
1a (1.0)
1a (1.0)
1a (1.0)c
1b (1.0)
1b (1.6)
None
MS4A
Alumina (neutral)
Alumina (basic)
nPr3N
MS4A
MS4A
MS4A
10
10
10
10
10
10
5
89 (17)
90 (27)
44 (16)
59 (16)
61 (11)
32 (9)
0/100
63/37
56/64
69/31
55/45
86/14
26/74
100/0
89 (19)
55 (4)
15
b
c
The number in parentheses is the isolated yield. CT and MS4A were mixed in Et2O
Total yields of 2 and 3 based on converted C60
.
before being added to the toluene solution of C60
.
act as a dehydrating agent. Basic alumina was more effective than
neutral alumina for the formation of 3a (Table 1, entries 3 and 4).
As well as 2a, fulleroid 3a was also yielded by the use of tripropyl
amine (Table 1, entry 5). From these results, the basicity and the
interaction between MS4A and chloramine 1a are important for
the formation of the azafulleroid. To enhance the interaction,
MS4A was mixed with 1a in diethyl ether, followed by removal of
the solvent. Next, the composite was treated with fullerene under
the same conditions to predominately yield the azafulleroid, as
expected (Table 1, entry 6). Ion-exchanged 1b, derived from
another commercially available chloramine-B, also effectively
introduced an N1 unit to C60 (Table 1, entry 7), and completely
selective formation of azafulleroid 3b was achieved when
1.6 equivalents of 1b were used (Table 1, entry 8).
N-benzenesulfonylaziridinofullerene 2b. Extending the reaction
time not only increased the yield of 3a and consumption of 2b, but
also produced N-benzensulfonylazafulleroid 3b. Interestingly, a
catalytic amount of chloramine was found to be effective for the
rearrangement. For example, 2a was treated with 10 mol% of 1b in
the presence of MS4A in toluene at reflux for 5 h to give 3a in 73%
yield (Table 2, entry 4).
Based on these results, a mechanism for the rearrangement of
aziridinofullerene is proposed as follows (Scheme 2, illustrated by a
part of fullerene).
To investigate the reaction pathway, isolated N-tosylaziridino-
fullerene 2a and MS4A were heated in toluene under reflux, but
the reaction did not proceed at all. In contrast, when 2a was
treated with N-tosylated chloramine 1a under reflux in the
presence of MS4A, N-tosylazafulleroid 3a was produced
(Table 2, entry 1), indicating that 3a is formed from 2a.
Treatment of 2a with chloramine 1b, which has a benzenesulfo-
nyl group, under the same conditions gave a mixture of 3a and
Table 2 Rearrangement of aziridinofullerene with chloramines
Yield (%)a
Entry Chloramine (equivalents) Time/min 3a
3b 2a
2b
1
2
3
4
a
1a (1.0)
1b (1.0)
1b (1.0)
1b (0.1)
10
10
30
300
37b
5
62
73
—
0
15
0
20b
60
9
—
9
0
11
0
Determined by 1H NMR. Isolated yields.
b
Scheme 2 Plausible pathway for the rearrangement.
324 | Chem. Commun., 2008, 323–325
This journal is ß The Royal Society of Chemistry 2008

First, the most strained carbon12 on aziridinofullerene 2a is
attacked by a chloramine to give diaminated intermediate A.
The reaction, illustrated by the curved black arrows in
intermediate A (p-conjugated SN29 type reaction), leads to
thermodynamically stable azafulleroid 3a through closed, [5,6]-
bridged intermediate C. An alternative route to C—an SN1-type
reaction (shown by the curved blue arrow), elimination of Cl
and the R2-substituted nitrogen prior to attack of the
nitrogen anion—should be considered. The alternative
path, shown by the curved red arrows in A, generates intermediate
B via chlorine atom transfer. Intermediate B reacts in the same
way as A to afford 2b and 3b. Although the function of MS4A
is unclear at present, the ability to eliminate nitrogen
anions generated in situ may be enhanced by the sodium cation
in MS4A.
Notes and references
1 (a) A. Hirsch and M. Brettreich, Fullerenes: Chemistry and Reactions,
Wiley-VCH, Weinheim, 2005; (b) Fullerenes: Chemistry, Physics, and
Technology, ed. K. M. Kadich and R. S. Ruoff, Wiley, New York, 2000;
(c) N. Martin, Chem. Commun., 2006, 2093–2104.
2 T. Ishida, K. Tanaka and T. Nogami, Chem. Lett., 1994, 23, 561–562.
3 (a) M. Prato, Q. C. Li, F. Wudl and V. Luccini, J. Am. Chem. Soc.,
1993, 115, 1148–1150; (b) Having sulfonyl groups: L. Ulmer and
J. Mattay, Eur. J. Org. Chem., 2003, 2933–2940.
4 S. Kuwashima, M. Kubota, K. Kushida, T. Ishida, M. Ohashi and
T. Nogami, Tetrahedron Lett., 1994, 35, 4371–4374.
5 M. R. Banks, J. I. G. Cadogan, I. Gosney, P. K. G. Hodgson,
P. R. R. Langridge-Smith, J. R. A. Millar and A. T. Taylor,
Tetrahedron Lett., 1994, 35, 9067–9070.
6 X. Zhang, L. Gan, S. Huang and Y. Shi, J. Org. Chem., 2004, 69,
5800–5802.
7 The thermal rearrangement of aziridinofullerene to azafulleroid is
suggested uncertainly in ref. 3a.
8 (a) J. Averdung and J. Mattay, Tetrahedron, 1996, 52, 5407–5420; (b)
A. Ouchi, R. Hatsuda, B. Z. S. Awen, M. Sakuragi, R. Ogura, T. Ishii,
Y. Araki and O. Ito, J. Am. Chem. Soc., 2002, 124, 13364–13365.
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Science, 1995, 269, 1554–1556; (b) B. Nuber and A. Hirsch, Chem.
Commun., 1996, 1421–1422.
10 (a) T. Ando, S. Minakata, I. Ryu and M. Komatsu, Tetrahedron Lett.,
1998, 39, 309–312; (b) T. Ando, D. Kano, S. Minakata, I. Ryu and
M. Komatsu, Tetrahedron, 1998, 54, 13485–13494; (c) D. Kano,
S. Minakata and M. Komatsu, J. Chem. Soc., Perkin Trans. 1, 2001,
3186–3188; (d) S. Minakata, D. Kano, R. Fukuoka, Y. Oderaotoshi and
M. Komatsu, Heterocycles, 2003, 60, 289–298; (e) S. Minakata,
D. Kano, Y. Oderaotoshi and M. Komatsu, Angew. Chem., 2004,
116, 81–83, (Angew. Chem., Int. Ed., 2004, 43, 79–81).
In summary, the present study has established
a new
chloramine-based aziridination of C60 and demonstrated
an unprecedented rearrangement of aziridinofullerene to
azafulleroid using a combination of chloramine and MS4A.
The method has sufficient possibility for the synthesis of
diverse aziridinofullerenes and azafulleroids using N-chloro-
N-sodio derivatives.13 Although the function of MS4A
requires clarification, this is the first example of the ionic
introduction of an N1 unit to C60 and the reagent-
assisted rearrangement of the product. Work along this line, as
well as the expansion of the generality of the reaction, is currently
under way.
11 C. Bingel, Chem. Ber., 1993, 126, 1957–1959.
12 C. M. Rohlfing and P. A. Cahill, Mol. Phys., 1997, 91, 561–566.
13 (a) E. Herranz and K. B. Sharpless, J. Org. Chem., 1980, 45, 2710–2713;
(b) G. Li, H. H. Angert and K. B. Sharpless, Angew. Chem., 1996, 108,
2995–2999, (Angew. Chem., Int. Ed. Engl., 1996, 35, 2813–2817).
This work was partially supported by a Grant-in-Aid for
Scientific Research from the Japan Society for the Promotion of
Science.
This journal is ß The Royal Society of Chemistry 2008
Chem. Commun., 2008, 323–325 | 325