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Chemistry Letters Vol.38, No.4 (2009)
Production of a 15-membered Ring Orifice in Open-cage Fullerenes
by Double Photooxygenation of Azafulleroid
Houjin Hachiya and Yoshio Kabeꢀ
Department of Chemistry, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka 259-1293
(Received January 5, 2009; CL-090007; E-mail: kabe@kanagawa-u.ac.jp)
Photooxygenation of silyl-modified azafulleroids 1b and 1c
gave open-cage fullerenes having keto lactam 2b and 2c or
diketo imide 3b and 3c functional groups on 11- or 15-mem-
bered ring orifices. The high reactivity of the bridgehead double
bonds was estimated by ꢀ-orbital axis vector (POAV) analysis
comparing the bisfulleroid derivatives 5d, 5e, 6d, and 6e.
Among surface modification reactions of C60, singlet oxy-
gen (1O2) oxygenation of azafulleroid and bisfulleroid is the
key reaction in the production of open-cage-,1 hetero-,2 and en-
1
dohedral-fullerenes.3 The [2 + 2] addition of O2 to the elec-
tron-rich bridgehead double bonds of these fulleroids, followed
by symmetrical ring opening, results in the opening of a hole
in the fullerenes surface.1a,1d–1i When the first cage-opening
reaction of azafulleroid 1a was reported by Wudl and co-
workers,1a diketo imide 3a was suggested as an alternative pos-
sible structure in addition to the keto lactam 2a, as shown in
Scheme 1. However, the diketo imide 3a has remained unob-
served to date. Recently, we reported the selective synthesis of
silyl benzene azafulleroids.4i Herein, we report the photooxyge-
nation of these silyl-modified azafulleroids 1b and 1c undergo-
ing stepwise oxidation to afford the first diketo imide 3b and
3c via the keto lactam 2b and 2c as shown in Scheme 1. It
was demonstrated that whether the double photooxygenation
of azafulleroid and the related bisfulleroid takes place or not
can be predicted by ꢀ-orbital axis vector (POAV) analysis5 of
the bridgehead double bonds.
A solution of either 1b or 1c in o-dichlorobenzene in a pyrex
tube was irradiated with a halogen lamp under bubbling oxygen
for 5 h. The 1H NMR signals of methylene protons for 1b and 1c
at 4.23 and 3.44 ppm disappeared completely (1b is shown in
Figure 1). The new signals for 2b and 2c at 4.52/5.68 and
3.83/4.93 ppm with doublet couplings were observed together
with aziridinofullerenes 4b and 4c at 4.03 and 3.25 ppm (2b
and 4b are shown in Figure 1). After column chromatography
through silica gel (eluent: CS2), 2b and 2c were obtained in 85
and 90% yields, as dark brown solid together with 11 and 10%
yield of the aziridinofullerene 4b and 4c, formed by the photo-
Figure 1. 1H NMR spectra in CDCl3 solution; (a) 1b, (b) 2b,
(c) 3b, and (d) 4b.
m/z
Figure 2. MALDI-TOF mass spectra of 2b (left) and 3b (right)
in negative-ion reflectron mode.
chemical isomerization of 1b and 1c.4 The MALDI-TOF mass
spectra of 2b and 2c show molecular ion peaks at m=z 1039
(Mꢁ) and 853 (Mꢁ) (2b is shown in Figure 2), indicating that
the product was formed by the addition of O2 to 1b and 1c.
The 13C NMR spectra display two carbonyl carbons at 161/
194 and 161/194 ppm for keto lactams 2b and 2c. In the fuller-
ene skeleton regions, 59 and 56 signals were observed, respec-
tively, indicating C1 symmetry for 2b and 2c. The IR spectra
show two pairs of carbonyl groups at 1682/1726 and 1681/
1726 cmꢁ1, respectively.
Next, a solution of either 1b or 1c in o-dichlorobenzene in a
pyrex tube was irradiated for 30 h. The reaction mixtures were
monitored by 1H NMR spectroscopy. During the prolonged irra-
diation, the signals for 2b and 2c decreased in intensity with a
concomitant increase in the singlet peaks at 5.24 and 4.49 ppm
(3b is shown in Figure 1). After chromatographic separation
(eluent: CHCl3), 3b and 3c were isolated in 9 and 11% yields,
with 58 and 44% yields of 2b and 2c recovered.6 The final prod-
ucts are suggested to be the diketo imide 3b and 3c on the basis
of the observed 1H and 13C NMR and MALDI-TOF mass spec-
tra. The molecular ion peaks at m=z 1071 (Mꢁ) and 885 (Mꢁ)
Scheme 1.
Copyright Ó 2009 The Chemical Society of Japan
Hachiya, Houjin
