PhI(OAc)2/I2-mediated [3+2] reaction of [60]fullerene with amides for the preparation of fullerooxazoles

Article abstract of DOI:10.1016/j.tetlet.2013.09.002

An efficient synthesis of fullerooxazoles was developed via PhI(OAc) ₂/I₂-mediated [3+2] reaction of C₆₀ with amides under photo-irradiation. The reaction was tolerant to various aryl and alkyl amides. The reaction mechanism was investigated in detail and a radical pathway was proposed for the formation of fullerooxazoles. Further transformation of compound 2l allowed the easy conjunction of fullerooxazole moiety to other molecular skeletons.

Full text of DOI:10.1016/j.tetlet.2013.09.002

Tetrahedron Letters 54 (2013) 6799–6803
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
PhI(OAc)2/I2-mediated [3+2] reaction of [60]fullerene with amides
for the preparation of fullerooxazoles
⇑
⇑
Hai-Tao Yang , Wen-Long Ren, Chun-Ping Dong, Yang Yang, Xiao-Qiang Sun, Chun-Bao Miao
School of Petrochemical Engineering, Changzhou University, Changzhou 213164, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 July 2013
Revised 25 August 2013
Accepted 2 September 2013
Available online 8 September 2013
An efficient synthesis of fullerooxazoles was developed via PhI(OAc)2/I2-mediated [3+2] reaction of C60
with amides under photo-irradiation. The reaction was tolerant to various aryl and alkyl amides. The
reaction mechanism was investigated in detail and a radical pathway was proposed for the formation
of fullerooxazoles. Further transformation of compound 2l allowed the easy conjunction of fullerooxazole
moiety to other molecular skeletons.
Ó 2013 Published by Elsevier Ltd.
Keywords:
Fullerene
Amides
PhI(OAc)2
Iodine
Photo
The functionalization of [60]fullerene with new structures and
properties is an important subject in fullerene chemistry for fur-
ther material and medicinal applications.1 A remarkable array of
their chemical reactions have been explored over the last two
decades.2 Cycloaddition reaction plays an important role in the
preparation of C60 derivatives, among which, 1,3-dipolar cycload-
dition reaction is the commonly used method to synthesize five-
membered ring-fused [60]fullerene derivatives containing one or
two hetero-atoms. Fulleroisoxazolines can be easily prepared from
the reaction of C60 with the in situ generated nitrile oxide.3 How-
ever, there were only a few reports on fullerooxazoles, as isomer
of fulleroisoxazolines, in the literatures (Scheme 1): (1) photo-
chemical reactions of C60 with acylazides4 or thermal reactions of
ber of oxazoline-containing natural products and biologically ac-
tive compounds are present in marine organisms8 and oxazoline
derivatives are also widely used as ligands in organic synthesis.
Thus, the development of a practical and convenient method for
the construction of an oxazoline ring is demanded. In continuation
of our interest in fullerene chemistry,9 herein we report the
PhI(OAc)2/I2-mediated [3+2] type reaction of fullerene with amides
under photo-irradiation to give fullerooxazole derivatives.10
Recently, treatment of alkenes with NBS/nitriles/NaHCO3/water
in the presence of metal triflates or with amides/tert-butyl hypoio-
dite was reported to furnish oxazoline compounds.11 Inspired by
their results, we wanted to apply their methods in the preparation
of fullerooxazoles from the easily available amides through a [3+2]
reaction. Therefore, a model reaction between C60 and benzamide
was carried out (Table 1).
C
60 with azidoformates and hydroxamic acid derivatives,5 followed
by rearrangement of the formed fulleroaziridines to fullerooxaz-
oles; (2) the Gao group reported the electrochemical method to
generate fullerooxazoles through aerobic oxidations of dianionic
C60 in PhCN solution;6 (3) the Wang group developed a one-step
approach starting from nitriles mediated by Fe(ClO4)3Á6H2O.7 Nev-
ertheless, these reactions have some limitations. The reaction of
C60 with acylazides always produces the azafulleroid as by-prod-
uct. Furthermore, the azides are classified as highly explosive and
toxic. Electrochemical method is not practical and always gener-
ates many by-products. Wang’s method needs an excessive
amount of nitriles up to 100 equiv. On the other hand, a great num-
Firstly, a similar operation method as that of Minakata10 and
Hajra’s10 was applied, but no reaction occurred (Table 1, entries
1 and 2). Next, we attempted the ionic reaction pathway through
an iodination-nucleophilic attack-cyclization process to generate
the fullerooxazole 2. A mixture of C60, benzamide, I2, and a base
C602-, O2
(Gao's work)
C60, Fe(ClO4)3
(Wang's work)
PhCN
R-CN
O
O
O
N
C60
this work
R
N
R
NH2
R
(Banks, Mattay,
⇑
Corresponding authors.
E-mail addresses: yht898@yahoo.com (H.-T. Yang), estally@yahoo.com (C.-B.
and Abrahom' swork)
Miao).
Scheme 1. Previous methods for the preparation of fullerooxazoles.
0040-4039/$ - see front matter Ó 2013 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.tetlet.2013.09.002

6800
H.-T. Yang et al. / Tetrahedron Letters 54 (2013) 6799–6803
Table 1
Optimization of the reaction conditions
O
O
O
conditions
+
N
NH2
N
1a
×
2a
Entry
Conditions
Temp (°C)
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
9
1a (1 equiv), NBS (1 equiv), Na2CO3 (1 equiv), Zn(OTf)2 (0.1 equiv)
1a (1 equiv), t-BuOCl (1 equiv), n-Bu4NI (1 equiv)
1a (1 equiv), I2 (1 equiv), Na2CO3 or DBU(2 equiv)
1a (1 equiv), I2 (1 equiv), PhI(OAc)2 (1 equiv)
1a (1 equiv), PhI(OAc)2 (1 equiv)
1a (2 equiv), I2 (2 equiv), PhI(OAc)2 (2 equiv)
1a (3 equiv), I2 (3 equiv), PhI(OAc)2 (3 equiv)
1a (4 equiv), I2 (4 equiv), PhI(OAc)2 (4 equiv)
1a (2 equiv), I2 (2 equiv), PhI(OAc)2 (2 equiv)
1a (2 equiv), I2 (0.2 equiv), PhI(OAc)2 (2 equiv)
1a (2 equiv), I2 (2 equiv), PhI(OAc)2 (2 equiv), dark
1a (2 equiv), I2 (2 equiv), PhI(OAc)2 (2 equiv), 250 W Hg lamp
25
25
25
25
25
25
25
25
60
25
40
40
24
24
24
16
24
16
7
Nr
Nr
Nr
15 (84)
Nr
24 (72)
26 (75)
27 (69)
21 (67)
<4
4
12
36
72
5
10
11
12
10 (83)
26 (77)
a
Isolated yield; the values in parentheses are based on consumed C60
.
was stirred at room temperature for 24 h. Neither Na2CO3 nor DBU
was effective in the reaction (Table 1, entry 3). When PhI(OAc)2
(DIB), an oxidant was used instead of the base, to our delight, the
expected fullerooxazole 2a was produced as a single product in
15% yield without the formation of an azirdinefullerene (Table 1,
entry 4). It was worth noting that I2 and PhI(OAc)2 were both cru-
cial to the successful [3+2] reaction and no reaction occurred in the
absence of either one (Table 1, entries 3 and 5). Increasing the
amount of I2 and PhI(OAc)2 to 2 equiv led to a noticeable improve-
ment on the yield to 24% (Table 1, entry 6). No dramatic improve-
ment on the yield of 2a could be achieved by further increasing the
amount of I2 and PhI(OAc)2 to 3–4 equiv or increasing the temper-
ature to 60 °C, albeit the reaction proceeded faster (Table 1, entries
7–9). Catalytic amount of I2 resulted in only below 4% yield of 2a
(Table 1, entry 10). An interesting phenomenon was observed that
only 9% yield of 2a was generated after 72 h if the reaction was
performed under dark (Table 1, entry 11), which indicated that
the light had great influence on the reaction. When a mixture of
NMR (Scheme 2 and Fig. 1).17 When the molar ratio of 1c, I2, and
DIB was 1:0.5:0.5, the reaction proceeded smoothly (Fig. 1c–f)
and the decomposition of DIB with a concomitant formation of
iodobenzene (#) and HOAc was observed clearly. Meanwhile, 4-
chlorophenyl isocyanate (j) and an unidentified active species
(N) were generated. Surprisingly, the active species (N) disap-
peared and gradually converted back to 1c with the extension of
time (Fig. 1f). It could also be seen that the amount of DIB and I2
was not enough because most of 1c remained. By increasing the
amount of I2 and DIB to 1.2 equiv, most of the amide 1c disap-
peared (see Supporting Information).
On the basis of those suggested mechanism for I2/DIB system11–
15 and our own 1H NMR studies, a possible reaction pathway can be
proposed. The molecular iodine is converted into acetyl hypoiodite
(CH3CO2I) via oxidation by DIB.18 Acetyl hypoiodite, as a good
source of I+, reacts with 1c to generate such active species as 4-
chloro-N,N-diiodobenzamide 4 (N) (Fig. 1c–e), which we first as-
sumed as an unidentified species. Two N–I bond cleavages of 4
yielded the nitrene intermediate, which undergoes rearrangement
to produce 4-chlorophenyl isocyanate. The formation of fulleroox-
azole can be explained by the addition of nitrene intermediate in
C60, benzamide, I2, and PhI(OAc)2 was stirred at 40 °C under the
photo-irradiation of 250 W high pressure mercury lamp, the reac-
tion proceeded quickly and afforded 2a in 26% yield within 5 h
(Table 1, entry 12).
its 1,3-dipolar mesomeric form to C60
.
The combination of DIB and I2, which was deemed to generate
acetyl hypoiodite, has been used by Suárez et al. to produce the
alkoxyl radicals in order to promote b-fragmentations or intramo-
lecular 1,5-/1,6-hydrogen atom transfer.12 Sulfonamidyl,13 phos-
phoramidyl, carbamoyl, and amidyl radical,14 could also be
generated easily using I2/DIB system for further transformation
such as intra-/inter-molecular amination of sp3 C–H bond or 1,5-
hydrogen atom transfer reaction.15 The redox chemistry between
hypervalent iodine and molecular iodine has also been reported
to generate active hypoiodous acid for iodohydroxylation of
alkenes.16
To substantiate this mechanism, equal amounts of I2 and
PhI(OAc)2 were mixed in CDCl3. Contrary to our expectations, only
very little CH3CO2I was detected even after 15 h (see Supporting
Information). However, when 10
lL of water was added to the
mixture of I2 and PhI(OAc)2 in CDCl3, a quick reductive decomposi-
tion of DIB to iodobenzene took place. This result demonstrated
that the combination of DIB and I2 did not take the same effect
as those reported in the literature to generate CH3CO2I because
dry toluene was selected as the solvent in all our experiments.
To understand the actual action of DIB, the reaction of 1c with
DIB in the absence of I2 was monitored by 1H NMR (see Supporting
Information). To our surprise, the generation of 4-chlorophenyl
isocyanate and iodobenzene could also be observed. The biggest
difference was that no active species (N) was detected in the ab-
sence of I2. In combination with the fact that the reaction of C60
with benzamide, and DIB failed to give fullerooxazole 2a in the ab-
sence of I2 (Table 1, entry 5), we concluded that: (i) the active spe-
cies (N) was the crucial intermediate to generate fullerooxazole 2a;
(ii) the combination of amide with DIB did not yield the nitrene
intermediate; (iii) 4-chlorophenyl isocyanate was not generated
To learn the details of the reaction process, the reaction of 4-
chlorobenzamide 1c with I2 and PhI(OAc)2 was examined by 1H
O
O
N
I
I2, PhI(OAc)2
CDCl3
C
NH2
N
I
+
Cl
O + PhI + HOAc
Cl
Cl
Scheme 2. Investigation on the reaction mechanism.

H.-T. Yang et al. / Tetrahedron Letters 54 (2013) 6799–6803
6801
Figure 1. 1H NMR spectra in CDCl3. (a) 4-Chlorobenzamide (b) PhI(OAc)2 (c–f) amide: I2:PhI(OAc)2 = 1:0.5:0.5.
from either the rearrangement of the anticipated nitrene interme-
diate or the active species (N). No formation of azirdinefullerene
unambiguously confirmed that nitrene did not exist in the reaction
as an intermediate.
Once the optimized conditions were established (Table 1, entry
12), we examined the scope and limitation of this kind of [3+2]
type reaction (Table 2). It could be seen that the reaction was tol-
erant to various functional groups. Aryl amides with either elec-
tron-donating or electron-withdrawing group on the phenyl ring
On the base of these results, an alternative plausible reaction
pathway is proposed in Scheme 3. The reaction of DIB with amide
1 generates iminophenyliodinane 3, which undergoes rearrange-
ment to give isocyanate accompanying with the loss of iodoben-
O
O
zene.19 In the presence of I2,
3 can be converted to key
H
R
N
H
R N C O
R
R
N
intermediate 4-chloro-N,N-diiodobenzamide 4, which cannot
transform to either nitrene or isocyanate. N–I bond cleavage of
4 produces the nitrogen radical 5, which is captured by C60 to
generate the fullerene radical 6. The second N–I bond cleavage
of 6 generates biradical 8, which isomerizes to 9 and subsequent
intramolecular coupling reaction affords 2. Photo-irradiation
accelerates the reaction notably because it is beneficial to the
N–I bond cleavage. If C60 does not exist in the reaction mixture,
4 can convert back to amide 1 gradually in the presence of trace
amounts of water (Fig. 1f). There is a competition between the
formation of 4 and isocyanate. Thus, increasing the amount of I2
is beneficial to the formation of 4 (Table 1, entry 6 vs 10). In addi-
tion, the poor solubility of DIB and amide in toluene results in rel-
atively high concentration of I2 in the solution, which is also
beneficial to transformation of 3 to 4. These factors will facilitate
the reaction.
1
CH3COOI
H2
O
×
×
I2
I2
O
×
O
RCONH2
O
I
I
N-I cleavage
- I
1
N
I
R
R
N
PhI(OAc)2
IPh
N
5
4
3
I
N
N
C60
N-I cleavage
- I
R
R
O
O
6
8
N
N
O
coupling
R
R
O
9
2
Scheme 3. Plausible mechanism.

6802
H.-T. Yang et al. / Tetrahedron Letters 54 (2013) 6799–6803
Table 2
CF3COO
NH3
Preparation of fullerooxazolesa
N
O
NHBoc
N
O
TFA
ODCB
I2 (2 equiv)
2l
O
10
O
R
N
PhI(OAc)2 (2 equiv)
l
C
t
r
+
O
C
Et3N
PhN=C=O
ODCB, rt
R
NH2
dry toluene
250 W Hg lamp
h
P
,
N
,
t3
B
C
E
1
2
OD
O
O
N
N
O
Ph
Entry
1
Substrate
Time
Product
Yieldb (%)
26 (77)
N
H
N
H
N
H
Ph
O
O
11
12
1a
4
2a
NH2
Scheme 4. The transformation of 2l.
O
1b
MeO
2
3
4
3.5
2b
2c
2d
29 (88)
23 (85)
20 (75)
NH2
isocyanate to give 11 and 12, respectively (Scheme 4). This trans-
formation allowed the easy conjunction of fullerooxzole moiety
to other molecular skeletons for further investigation of their prop-
erties and applications.
In summary, PhI(OAc)2/I2 system has been successfully utilized
in the [3+2] type reaction between C60 and amides at the first time
for the preparation of fullerooxazole derivatives. Photo-irradiation
has notable acceleration effect on this reaction. The present meth-
od provided a convenient one-step route for the synthesis of
fullerooxazoles under metal-free conditions.
O
1c
Cl
5
6
NH2
O
1d O2N
NH2
O
O2N
5
6
7
5
5
5
2e
2f
24 (79)
30 (86)
23 (88)
NH2
1e
O
NH2
1f
Acknowledgment
N
CONH2
We are grateful for financial support from the National Natural
Science Foundation of China (Nos. 20902039 and 21202011).
2g
1g
O
Supplementary data
1h
8
9
6
6
2h
2i
17 (77)
25 (81)
NH2
Supplementary data (the examination of PhI(OAc)2/I2/amide,
PhI(OAc)2/amide, and PhI(OAc)2/I2 system tracked by 1H NMR in
CDCl3 and NMR Spectra of 2a–c, 2e–l, 11, and 12) associated with
this article can be found, in the online version, at http://dx.doi.org/
10.1016/j.tetlet.2013.09.002.
EtO
O
1i
O
NH2
O
NH2
10
11
5
5
2j
21 (81)
19 (79)
1j
O
References and notes
1k
2k
NH2
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