Photochemical synthesis, conformational analysis, and transformation of [60]fullerene-o-quinodimethane adducts bearing a hydroxy group

Article abstract of DOI:10.1021/jo0161328

The photochemical reactions of [60]fullerene with various aromatic aldehydes or ketones 1a-n carrying an alkyl group at the ortho position were examined. Some of them afforded stable o-quinodimethane adducts 2 with a hydroxy group attached to the cyclohexene ring. The adducts 2 were found to adopt one or both of two conformers A and E, which possess pseudoaxial and pseudoequatorial hydroxy groups, respectively. The conformer ratios depended remarkably on the substituents attached to the aromatic nucleus and the cyclohexene ring. The dynamic behavior of 2 was also investigated by the VT-NMR technique.

Full text of DOI:10.1021/jo0161328

J . Org. Chem. 2002, 67, 1247-1252
1247
P h otoch em ica l Syn th esis, Con for m a tion a l An a lysis, a n d
Tr a n sfor m a tion of [60]F u ller en e-o-qu in od im eth a n e Ad d u cts
Bea r in g a Hyd r oxy Gr ou p
Yosuke Nakamura, Kyoji O-kawa, Satoshi Minami, Toshio Ogawa, Seiji Tobita, and
J un Nishimura*
Department of Chemistry, Gunma University, Tenjin-cho, Kiryu, Gunma 376-8515, J apan
nisimura@chem.gunma-u.ac.jp
Received September 20, 2001
The photochemical reactions of [60]fullerene with various aromatic aldehydes or ketones 1a -n
carrying an alkyl group at the ortho position were examined. Some of them afforded stable
o-quinodimethane adducts 2 with a hydroxy group attached to the cyclohexene ring. The adducts
2 were found to adopt one or both of two conformers A and E, which possess pseudoaxial and
pseudoequatorial hydroxy groups, respectively. The conformer ratios depended remarkably on the
substituents attached to the aromatic nucleus and the cyclohexene ring. The dynamic behavior of
2 was also investigated by the VT-NMR technique.
In tr od u ction
of benzocyclobutenes, the SO2 extrusion of sulfolenes or
sultines, or the iodide-induced 1,4 elimination of 1,2-bis-
(bromomethyl)benzene derivatives.7 These precursors,
however, are not necessarily easily available. Further-
more, the generation of o-quinodimethane from benzo-
cyclobutenes requires rather high temperatures, which
can lead to undesirable side reactions. In the iodide-
induced 1,4 eliminations of R,R′-dihalides, appropriate
phase-transfer catalysts such as 18-crown-6 are neces-
sary in addition to iodide sources because [60]fullerene
is almost insoluble in many polar organic solvents such
as DMF.
The photoirradiation of o-tolualdehyde (1a ) and related
carbonyl compounds is known to give an o-quinodimethane
species carrying a hydroxy group via the biradical gener-
ated by the intramolecular hydrogen abstraction of the
carbonyl group in the excited triplet state (n-π*) from
the neighboring methyl group.8 o-Quinodimethane readily
reacts with dienophiles, though it partially reverts to the
starting material. Hence, in principle, it seems possible
to obtain [60]fullerene-o-quinodimethane adducts by
using [60]fullerene as a dienophile. However, it is rather
difficult to efficiently produce the photoexcited states of
aromatic carbonyl compounds in the presence of [60]-
fullerene because the latter has stronger absorption
bands throughout most of the UV region. For this reason,
many of the known photochemical reactions involving
[60]fullerene have taken advantage of the excited triplet
state of [60]fullerene formed by intersystem crossing from
the singlet excited state.9
Among the functionalizations of [60]fullerene, Diels-
Alder reactions with o-quinodimethanes as dienes are
very versatile because they provide thermally stable
adducts that are usually not subjected to cycloreversion
into their original components.1-6 The high stability is
provided by the aromatic system generated in the ad-
ducts. o-Quinodimethane derivatives have been obtained
as reactive intermediates, mainly from the thermolysis
* Corresponding author. Telephone: +81-277-30-1310. Fax: +81-
277-30-1314.
(1) (a) Tago, T.; Minowa, T.; Okada, Y.; Nishimura, J . Tetrahedron
Lett. 1993, 34, 8461. (b) Nakamura, Y.; Minowa, T.; Tobita, S.; Shizuka,
H.; Nishimura, J . J . Chem. Soc., Perkin Trans. 2 1995, 2351. (c)
Nakamura, Y.; Minowa, T.; Hayashida, Y.; Tobita, S.; Shizuka, H.;
Nishimura, J . J . Chem. Soc., Faraday Trans. 1996, 92, 377.
(2) (a) Belik, P.; Gu¨gel, A.; Spickermann, J .; Mu¨llen, K. Angew.
Chem., Int. Ed. Engl., 1993, 32, 78. (b) Gu¨gel, A.; Kraus, A.; Spicker-
mann, J .; Belik, P.; Mu¨llen, K. Angew. Chem., Int. Ed. Engl. 1994, 33,
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Chem. 1995, 60, 3307. (d) Kraus, A.; Gu¨gel, A.; Walter, M.; Mu¨llen, K.
Tetrahedron, 1995, 51, 9927. (e) Gu¨gel, A.; Belik, P.; Walter, M.; Kraus,
A.; Harth, E.; Wagner, M.; Spickermann, J .; Mu¨llen, K. Tetrahedron,
1996, 52, 5007.
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Wudl, F. Tetrahedron Lett. 1995, 36, 8307. (b) Ferna´ndez-Paniagua,
U. M.; Illescas, B. M.; Mart´ın, N.; Seoane, C. J . Chem. Soc., Perkin
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dorf, H.; Thilgen, C. Helv. Chim. Acta 1993, 76, 2445. (b) Iyoda, M.;
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Mart´ın, N. Chem. Rev. 1999, 99, 3199.
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10.1021/jo0161328 CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/31/2002

1248 J . Org. Chem., Vol. 67, No. 4, 2002
Nakamura et al.
Ch a r t 1
The results of the photoreactions are summarized in
Table 1.
o-Tolualdehyde (1a : R1 ) R2 ) H) and o-ethylbenzal-
dehyde (1b: R1 ) H, R2 ) Me) afforded the corresponding
o-quinodimethane monoadducts 2a and b, respectively.
2a had been already prepared from benzocyclobutenol as
a precursor of hydroxy-o-quinodimethane by Foote et al.3
It is noteworthy that 2a can be obtained from com-
mercially available 1a in a single step. Although the
isolated yield listed here (32%) is lower than that
obtained by the reported method (59%),3 the yield based
on the consumed [60]fullerene amounts to 87%. The
irradiation of [60]fullerene was also investigated in the
presence of excess 1a . The yields of 2a and bisadducts
are listed in Table 2, along with the recovered [60]-
fullerene yield. With increasing amounts of 1a relative
to the amount of [60]fullerene, the isolated yields of 2a
and bisadducts gradually increased, and the recovery of
[60]fullerene decreased. The highest yield of 2a was
obtained for 1a /[60]fullerene ) 5:1. Using 9 equiv of 1a ,
the yield of 2a decreased while that of the bisadducts
further increased. The decreased yield of 2a under this
condition is ascribed to the formation of products with
higher polarity, probably trisadducts, in addition to the
formation of bisadducts. These results suggest that the
reactivity of 2a with 1a is comparable to that of [60]-
fullerene itself because the bisadditions should proceed
stepwise. The formation of bisadducts was confirmed by
mass spectrometry. Their 1H NMR spectra, however,
indicated the formation of complex mixtures of regioiso-
mers and stereoisomers, which were not subjected to
further purification.
In attempting to accomplish regioselective bisaddition,
we have also examined the reactions using precursors
1o-r containing two o-tolualdehyde moieties tethered by
oligomethylene or oligooxyethylene linkages of various
lengths. Generally, covalent linkages between two reac-
tive species effectively regulates their arrangement and
distance and enhances regioselectivity in bisaddition, as
demonstrated by several research groups.12 However,
there has so far been no example of the application of
this technique to photochemical reactions. The photoir-
radiation of 1o-r and [60]fullerene in benzene under
conditions similar to those mentioned above produced one
o-quinodimethane species that reacted with [60]fullerene
to yield monoaddition products 2o-r bearing an o-
tolualdehyde moiety intact. Even by further irradiation
of 2o-r , the remaining o-tolualdehyde moiety was un-
changed, and thus no desired bisadducts were obtained.
Because the intermolecular reaction between [60]fullerene
In this context, Tomioka et al. have examined the
photoreaction of o-methylbenzophenone (1f) with [60]-
fullerene.10 Unexpectedly, the desired adduct 2f was so
unstable that they isolated only the monoalkyl-1,2-
dihydrofullerene by the cleavage of the C-C bond con-
nected to the fullerene core. In contrast, we have recently
found that 1a and several related compounds afford
sufficiently stable [60]fullerene adducts.11 This reaction
is expected to be a useful method for preparing [60]-
fullerene-o-quinodimethane adducts. Thus, we have
further examined the reactions with various aromatic
carbonyl compounds carrying an alkyl group at the ortho
position. Here we report the versatility of this reaction,
the substituent effects on the reactivity and conforma-
tional behavior, and further functionalization of the
resulting adducts in detail.
Resu lts a n d Discu ssion
P h otor ea ction s Betw een [60]F u ller en e a n d 1a -
n . The photoreactions of [60]fullerene with 1a -n , shown
in Chart 1, were examined. The photoreaction with 1f
and the isolation of the resulting adduct were also
reexamined.
A 1:1 mixture of [60]fullerene and 1a -n in benzene (5
× 10-4 M) was irradiated with a 400 W high-pressure
mercury lamp in a Pyrex vessel with stirring at room
temperature for 6 h. These irradiation conditions can
produce the excited species of 1a -n as well as [60]-
fullerene, though the latter is predominantly already in
the excited state (e.g., the molar extinction coefficients
(ꢀ) of 1a and [60]fullerene are 1 × 102 and 2 × 104 at 313
nm, respectively). Among them, 1a , b, e, f, i, k , and m
gave the desired monoadducts 2 along with the recovered
[60]fullerene and a small amount of bisadducts (eq 1).
(10) Tomioka, H.; Ichihashi, M.; Yamamoto, K. Tetrahedron Lett.
1995, 36, 5371.
(11) O-kawa, K.; Nakamura, Y.; Nishimura, J . Tetrahedron Lett.
2000, 41, 3103.
(12) Diederich, F.; Kessinger, R. Acc. Chem. Res. 1999, 32, 537 and
references therein.

Photochemical Synthesis of C60-o-quinodimethane
J . Org. Chem., Vol. 67, No. 4, 2002 1249
Ta ble 1. P h otor ea ction of [60]F u ller en e w ith 1
dehyde (1i) gave adduct 2i, while 1j, bearing a hydroxy
group at the ortho position of the formyl group, led to
the recovery of [60]fullerene. In the excited state of 1j,
the proton transfer from the hydroxyl group to the
carbonyl group must be predominant, thus preventing
the hydrogen abstraction from the methyl group.13 In
contrast, 1k , carrying a hydroxy group at the para
position of the formyl group, successfully afforded 2k ,
though the yield was extremely low.
precursor
conformer
adduct yield/%a ratio (A/E)b
X
R1
R2
Y
1a
1b
1e
1f
CH
CH
CH
CH
CMe
CH
N
H
H
Me
Ph
H
H
Me
H
H
H
H
2a
2b
2e
2f
2i
32 (63)
17 (80)
9 (87)
4:6
H
H
H
H
0:10c
6:4
29d (69)
33 (58)
5 (89)
6:4
10:0
5.5:4.5
0:10
1i
1k
1m
H
H
H
H
OH 2k
2m
H
15 (83)
The irradiation of aldehydes consisting of polycyclic
aromatic or heteroaromatic rings was also examined.
2-Methyl-1-naphthaldehyde (1l) failed to give the desired
monoadduct. In aromatic aldehydes containing larger π
systems, the excited triplet state has π-π* character;14
this state cannot be involved in the hydrogen abstraction.
Intriguingly, monoadduct 2m was obtained from 1m ,
which has a pyridine ring, whereas only [60]fullerene was
recovered from 1n , which has a thiophene ring.
The obtained monoadducts, except for 2f, were easily
isolated as stable products by column chromatography
(silica gel), and no decomposition products were detected.
The purification of adducts is much easier than that in
the reactions using benzocyclobutenes or 1,2-bis(bro-
momethyl)benzene derivatives as o-quinodimethane pre-
cursors. In contrast, the isolation of 2f has been unsuc-
cessful, although 2f was a major product; a trace amount
(ca. 1-2%) of the monoalkyl 1,2-dihydrofullerene reported
in the literature10 was not completely removed, despite
several attempts to isolate 2f, including recrystallization,
HPLC, and GPC. Because this product was absent
immediately after the photoirradiation, it was apparently
formed during the purification process of 2f.
To clarify the reactive species involved in the photo-
reaction, a mixture of [60]fullerene and 1a was irradiated
at 532 nm by using an Nd:YAG laser, in which [60]-
fullerene can be exclusively photoexcited. Under these
irradiation conditions, intact [60]fullerene was recovered
without the formation of desired adducts. This observa-
tion apparently demonstrates that these photoreactions
require the excited states of carbonyl compounds, which
generate o-quinodimethane by intramolecular hydrogen
abstraction; the excited triplet state of [60]fullerene does
not react with the ground state 1a but decays back to
the ground state.
Considering the extremely small absorbance of carbo-
nyl compounds such as 1a relative to that of [60]fullerene
in the UV, it is noteworthy that the desired o-quin-
odimethane adducts were obtained by irradiation with a
high-pressure mercury lamp in the presence of [60]-
fullerene. The successful progress of this reaction indi-
cates that the o-quinodimethane is quite efficiently
formed from the excited triplet state of carbonyl com-
pounds and, subsequently, undergoes the Diels-Alder
reaction with [60]fullerene sufficiently fast within their
lifetimes. The high efficiency of these processes should
enable the seemingly unfavorable reaction, where the
incident light is only slightly absorbed by the component
(e.g., 1a ) that needs to be photoexcited.
a
Isolated yields are shown, although not optimized. Recovery
b
of [60]fullerene is also shown in parentheses. The symbols A and
E denote conformers possessing a pseudoaxial and a pseudoequa-
torial hydroxy group, respectively (see ref 3).
c Only a single conformer was obtained in which both the hydroxy
and methyl groups adopt pseudoequatorial conformations.
trace amount of the decomposition product is included.
d
A
Ta ble 2. Rea ction s of [60]F u ller en e w ith 1a u n d er
Va r iou s Con d ition s
isolated yields/%
molar ratio
monoadduct
recovery of
bisadduct [60]fullerene/%
of 1a /[60]fullerene
2a
1
3
5
9
32
40
45
18
trace
8
16
63
32
20
7
20
and 1a undoubtedly gave bisadducts, 2o-r should have
had sufficient reactivity for further photoreaction. The
bridging linkage used here, especially that in 1q or r ,
seems sufficiently flexible so that it is unlikely to prevent
the second addition because of steric hindrance. Thus,
the failure of the second o-tolualdehyde moiety to react
with [60]fullerene is interpreted as follows: The irradia-
tion of the monoadduct can produce the excited states of
the second o-tolualdehyde moiety, as in the case of the
first addition step. However, these excited states appear
to decay rapidly because of the intramolecular energy
transfer to the [60]fullerene moiety because the o-
tolualdehyde moiety is located relatively close to the
fullerene surface, in contrast to the intermolecular reac-
tion between 2a and 1a . Hence, no intramolecular
hydrogen abstraction that is necessary for the generation
of o-quinodimethane takes place. The photoirradiation
of 1o-r and [60]fullerene under the present conditions
also failed to give compounds carrying two [60]fullerene
moieties that reacted with both ends of 1o-r .
o-(Methoxymethyl)benzaldehyde 1c (R1 ) H, R2
)
OMe) yielded a product whose UV-vis spectrum indi-
cated a peak around 430 nm, which is characteristic of
1
[60]fullerene monoadducts. The H NMR spectra, how-
ever, were apparently inconsistent with the desired
o-quinodimethane adducts; there were no suitable cyclo-
hexene proton peaks. The identification of the products
has been so far unsuccessful. The irradiation of 1d (R1 )
H, R2 ) Ph) resulted in the recovery of [60]fullerene.
o-Methylacetophenone (1e) and o-methylbenzophenone
(1f) also produced the desired monoadducts, though the
yield using 1e was rather low. In contrast, no desired
adducts were formed from o-toluic acid (1g) and its
methyl ester (1h ).
Str u ctu r a l An a lysis of Mon oa d d u cts. The monoad-
ducts obtained here were characterized by MS, UV, and
NMR spectroscopy. 2a , b, e, f, i, k , and m had molecular
ion peaks corresponding to the desired monoadducts in
(13) Nagaoka, S.; Hirota, N.; Sumitani, M.; Yoshihara, K. J . Am.
Chem. Soc. 1983, 105, 4220.
(14) Kitamura, M.; Baba, H. Bull. Chem. Soc. J pn. 1975, 48, 1191.
The effects of the substituents directly attached to the
benzene ring were also examined. 2,6-Dimethylbenzal-

1250 J . Org. Chem., Vol. 67, No. 4, 2002
Nakamura et al.
Ta ble 3. Ch em ica l Sh ifts (δ) of Cycloh exen e-Rin g
Sch em e 2
P r oton sa
conformer
compound
OH
R1
Ha
R2
A
2a b
2e
2f
3.14
2.84
3.12
3.09
3.12
3.27
3.27
3.01
3.41
3.26
5.81
6.37 (H)
5.62
4.37 (H)
4.35 (H)
4.56 (H)
4.32 (H)
4.28 (H)
4.51 (H)
2.31 (Me)
4.50 (H)
4.26 (H)
4.40 (H)
4.53 (H)
2.71 (Me) 5.85
(Ph)c
5.85
5.61
5.57
4.82
4.66
2i
6.71 (H)
6.32 (H)
6.51 (H)
6.56 (H)
2k
2a b
2b
2e
2f
2k
2m
E
2.62 (Me) 5.08
(Ph)c
5.04
4.76
4.86
6.45 (H)
6.45 (H)
a
b
See Table 1 for each designation. These values agree with
those in reference 3. c Complex spectral patterns are observed.
Sch em e 1
dienol, for which four isomers I-IV are possible, under-
goes a Diels-Alder reaction with [60]fullerene to give 2b
(Scheme 2). Among them, (Z)-dienols II and IV are
known to revert rapidly to the original aldehyde via a
[1,5]-sigmatropic hydrogen shift.15 Of (E)-dienols I and
III, I, which can lead to 2b-E,E, appears to be more
stable than II because of less steric hindrance. The PM3
calculations suggest that I is more stable than III by 3.0
kcal/mol. Such relative stability results in the exclusive
formation of 2b-E,E, which is unlikely to convert into 2b-
A,A because of the flagpole steric hindrance, thus result-
ing in the observation of the single conformer.
the FAB-MS spectra. Their UV-vis spectra were sub-
stantially identical to each other, despite the difference
in substituents. All of these monoadducts displayed a
sharp band around 430 nm and a weak band around 700
nm. These bands are characteristic of [60]fullerene
monoadducts.1,2 1H NMR spectra provided the most
decisive information on the structure and conformation
of adducts. The chemical shifts of cyclohexene-ring
protons are listed in Table 3.
The 1H NMR spectra of both 2e and f indicated the
existence of two conformers similar to 2a , although an
inseparable decomposition product was also involved in
2f, as described above. The assignment of each conformer
was established by comparison with the chemical shifts
of 2a ; in conformer E, the hydroxy proton resonates at a
lower field than it does in conformer A, while the Ha
proton resonates at a higher field. On the basis of these
observations, the major conformers for 2e and f were
assigned as A, which possesses a pseudoaxial hydroxy
group, in contrast to that of 2a . The conformer ratio A/E
was 6:4 for both 2e and f. The decrease in the ratio of E
in 2e and f relative to that of 2a seems to result from
the destabilization of E caused by the steric hindrance
between the Ha proton and the R1 (methyl or phenyl)
group.
As reported by Foote et al.,3 2a is composed of two
conformers 2a -A and 2a -E possessing a pseudoaxial and
a pseudoequatorial hydroxy group, respectively, that
slowly exchange on the NMR time scale at room tem-
perature. The conformer ratio A/E was 6:4, which is
approximately in agreement with that reported in the
literature.3
Adduct 2b obtained from 1b carries another substitu-
ent on the cyclohexene ring. Therefore, two diastereo-
isomers, cis and trans isomers, are possible for 2b, each
of which can be composed of two conformers, as shown
1
in Scheme 1. Intriguingly, the H NMR spectrum of 2b
indicated the existence of a single conformer of one
diastereoisomer. Its stereochemistry was readily deter-
mined on the basis of NOE experiments. Because NOE
interaction was observed between the two protons di-
rectly attached to the cyclohexene ring, the hydroxy and
methyl groups were both assigned as pseudoequatorial
(2b-E,E). This assignment is also supported by the
similarity of chemical shifts of the cyclohexene and OH
protons in 2b to those in 2a -E rather than to those in
2a -A (Table 3). The absence of the trans isomer (2b-E,A
or 2b-A,E) and conformer 2b-A,A of the cis isomer is
apparently related to the stereochemistry of reaction
intermediates generated from 2b. As described above, the
intramolecular hydrogen abstraction of 2b affords an
o-quinodimethane species with a hydroxy group (i.e.,
dienol) via quite a short-lived biradical.6 The resulting
The interconversion between conformers E and A in
2e was investigated by the variable-temperature (VT)
NMR technique. Foote et al. estimated the ∆Gq value for
2a to be 17.6 kcal/mol.3 This value is much larger than
that for the [60]fullerene-o-quinodimethane adduct with
no hydroxy group on the cyclohexene ring (15.2 kcal/
mol).1b The higher barrier for 2a is attributable to the
presence of the hydroxy group, which should destabilize
the transition state and make the inversion difficult. In
2e bearing two geminal substituents, the methyl group
coalesced at 120 °C in Cl2CDCDCl2, whereas two sets of
cyclohexene protons Ha and R2 did not coalesce even at
this temperature, though there was slightly broadening
(15) Haag, R.; Wirz, J .; Wagner, P. J . Helv. Chim. Acta 1977, 60,
2595.

Photochemical Synthesis of C60-o-quinodimethane
J . Org. Chem., Vol. 67, No. 4, 2002 1251
Ta ble 4. Activa tion F r ee En er gies (∆Gq) for Rin g
with increasing temperature. On the basis of the coales-
cence temperature of the methyl group, the ∆Gq value
was estimated to be 19.6 kcal/mol. It is apparent that
the additional methyl group further prevents the ring
inversion relative to 2a .
In ver sion in Ad d u cts
adduct
∆Gq/kcal mol-1
2a
2e
4
5
6
17.6 ( 0.3a
19.6 ( 0.3
17.2 ( 0.3
17.1 ( 0.3
16.8 ( 0.3
The 1H NMR spectrum of 2m produced from 1m
showed a single conformer that was similar to 2b. This
result is in remarkable contrast to 2a , which consists of
two conformers. On the basis of NOE experiments, the
hydroxy group was found to adopt a pseudoequatorial
conformation similar to that of 2b; NOE interaction was
observed between the R1 and Ha protons. The addition
of trifluoroacetic acid to 2m induced considerable low-
a
Reference 3.
have examined the o-acylation of 2m bearing a pyridine
residue and have prepared 4, 5, and 6 with a phenyl, a
1-naphthyl, and a 9-anthryl group, respectively (eq 3).
1
field shifts in the H NMR spectrum, especially for the
pyridine protons, indicating the protonation at the ni-
trogen atom, while only conformer E was still observed.
These results suggest that the hydrogen bonding between
the pyridine nitrogen atom and the hydroxy group is not
responsible for the exclusive presence of conformer E in
2m . The preference for E is probably ascribable to less
steric interaction between the hydroxy group and the
pyridine nitrogen atom than that found in 2a -E, which
possesses a phenyl C-H proton. This steric interaction
was clearly demonstrated by the structural analysis of
2i. Intriguingly, 2i was composed of a single conformer,
which was assigned as A on the basis of the comparison
The o-acylation of 2m with benzoyl chloride and
1-naphthoyl chloride was carried out in the presence of
4-(dimethylamino)pyridine (DMAP) and pyridine in CH2-
Cl2, in a manner similar to that reported by Foote et al.,3
to yield esters 4 and 5, respectively. For the preparation
of 6, 2m was allowed to react with 9-anthroic acid in the
presence of DCC and DMAP in toluene. 4, 5, and 6 are
composed of two conformers each, in contrast to 2m . The
introduction of acyl groups into the hydroxy group of 2m
increases the steric interaction with the pyridine nitrogen
atom, leading to the destabilization of conformer E
relative to that of A. In each of 4-6, the conformer ratio
A/E was estimated to be approximately 1:1. The dynamic
behavior of A and E was examined by VT-NMR in Cl2-
CDCDCl2 in a manner similar to that used with 2e.
Unfortunately, the coalescence of singlet peaks for the
cyclohexene methine (R1) proton was not clearly observed
because they overlapped with the signals of some of the
aromatic protons. Instead, the pyridine R-protons were
found to coalesce at 70 °C for both 4 and 5 and at 60 °C
for 6. On the basis of these temperatures, the ∆Gq values
for 4, 5, and 6 were estimated to be 17.2, 17.1, and 16.8
kcal/mol, respectively. These values are comparable to
that for 2a (Table 4). The difference in the aromatic
nuclei was not so significantly reflected in the ∆Gq values.
1
with the H NMR spectral data of 2a ; the chemical shifts
of the OH, Ha, and R2 protons are comparable to those of
2a -A rather than to those of 2a -E (Table 3). The differ-
ence in the conformer ratios among 2a , 2m , and 2i is
remarkable; 2m adopts only E, 2a , both A and E (4:6),
and 2i, only A. These differences apparently correspond
to the bulkiness of the X site of the aromatic ring; the
value of A/E increases in the order X ) N < CH < CCH3.
In 2k , two conformers A and E were observed and were
similar to those of 2a . However, A was slightly predomi-
nant over E (A/E ) 55:45), in contrast to the value of
A/E for 2a . The relatively high stability of conformer A
in 2k seems to be ascribed to some electronic effects of
the hydroxy group that is attached to the benzene ring
because this substituent is unlikely to affect sterically
the relative stability of the two conformers.
F u n ction a liza tion of Ad d u cts Obta in ed . The hy-
droxy group of the monoadducts that were obtained is
available for further functionalizations, which can alter
the conformational behavior and also provide the adducts
with additional properties.
First, we have examined the oxidation of 2a , which
should transform two conformers into a single entity. 2a
was allowed to react with excess PCC in CH2Cl2/CS2
(1:1) at room temperature for 3 h to give the desired
Su m m a r y
1
product 316 (eq 2). In the H NMR spectrum of 3, the two
Stable o-quinodimethane adducts 2a , b, e, i, k , and m
possessing a hydroxy group that is applicable to further
transformations were obtained from photochemical reac-
tions between the corresponding carbonyl compounds and
[60]fullerene. A and E conformers existed for 2a , e, and
k , while 2b, i, and m exclusively adopted E, A, and E
conformations, respectively. The conformer ratios were
mainly dependent on the bulkiness of the substituents
attached to the aromatic or cyclohexene ring, as clearly
demonstrated by 2a , i, and m . 2m , bearing a pyridine
ring, was successfully transformed into esters 4-6, which
adopted two conformations.
cyclohexene protons were observed at δ 4.82 as a sharp
singlet, indicating that the inversion is sufficiently fast
on the NMR time scale, in contrast with that of 2a . Such
fast inversion was also demonstrated by the 13C NMR
spectrum showing Cs symmetry.
The conversion of the hydroxy group of 2a into an ether
(16) Tomioka, H.; Yamamoto, K. J . Chem. Soc., Chem. Commun.
1995, 1961.
or an ester group was investigated by Foote et al.3 We

1252 J . Org. Chem., Vol. 67, No. 4, 2002
Nakamura et al.
145.26, 145.21, 144.85, 144.66, 144.47, 144.40, 143.11, 142.93,
142.62, 142.57, 142.39, 142.23, 142.08, 141.94, 141.90, 141.79,
141.69, 141.59, 141.57, 141.55, 140.27, 140.08, 139.84, 139.10,
135.86, 135.81, 135.72, 135.63, 135.15, 130.50, 123.94, 73.28
(CHOH), 71.31, 65.22 (C60 sp3-C), 42.05 (CH2); FAB MS m/z
841 (M+).
Exp er im en ta l Section
Gen er a l. NMR spectra were recorded on a J EOL R-500 FT-
NMR spectrometer with tetramethylsilane as an internal
standard. FAB and APCI mass spectra were taken by a J EOL
J MS-HX110A and a Shimadzu LC-MS QP-8000 mass spec-
trometer, respectively. Absorption spectra were recorded on a
Hitachi U3210 spectrophotometer. Carbonyl compounds 1a ,
e-i, and n were commercially available, whereas 1b,17 c,18 d ,8a
l,19 and m 20 were prepared by the lithiation of the correspond-
ing bromides with n-butyllithium, followed by treatment with
DMF.21 1j22 and k 23 were prepared by the formylation of 2,5-
dimethylphenol and m-cresol, respectively, with dichloro-
methyl methyl ether and TiCl4.
Gen er a l P r oced u r e for th e P h otor ea ction of [60]-
F u ller en e a n d Ca r bon yl Com p ou n d s. A mixture of carbon-
yl compound 1b (33.5 mg, 0.25 mmol) and [60]fullerene (180
mg, 0.25 mmol) in benzene (500 mL) was irradiated with a
400 W high-pressure mercury lamp in a Pyrex vessel at room
temperature for 6 h. The reaction mixture was chromato-
graphed on silica gel (toluene/hexane 4:1) to give unreacted
[60]fullerene, monoadduct 2b, and bisadducts. 2b was obtained
as brown powder (36 mg, 17%). The reaction also proceeded
under sunlight.
P r ep a r a tion of 3 by th e Oxid a tion of 2a . A mixture of
2a (84 mg, 0.10 mmol) and PCC (107 mg, 0.50 mmol) in CS2/
CH2Cl2 (20 mL) was stirred at room temperature for 3 h. The
reaction mixture was chromatographed on silica gel (toluene/
hexane (4:1)) to give ketone 316 as a brown powder (51 mg,
1
61%). H NMR (CDCl3, 500 MHz) δ 8.12 (1H, d, J ) 7.7 Hz),
7.84 (1H, t, J ) 7.7 Hz), 7.74 (1H, t, J ) 7.7 Hz), 7.69 (1H, d,
J ) 7.7 Hz), 4.82 (2H, s); 13C NMR (CDCl3, 125 MHz) δ 193.50
(CdO), 155.41, 152.14, 147.67, 147.52, 147.21, 146.50, 146.26,
146.22, 145.68, 145.61, 145.47, 145.41, 144.89, 144.60, 144.57,
142.99, 142.69, 142.62, 142.29, 142.02, 141.79, 141.76, 141.60,
141.53, 140.45, 140.13, 137.91, 135.62, 135.29, 135.27, 134.46,
128.63, 128.29, 127.78, 63.30 (C60 sp3-C), 43.98 (CH2) (Some
peaks are missing because of the overlap.); IR ν(CdO) 1689
cm-1; FAB MS m/z 838 (M+).
P r ep a r a tion of Ester 4. A mixture of 2m (42 mg, 0.050
mmol), benzoyl chloride (46.2 µL, 0.40 mmol), 4-(dimethylami-
no)pyridine (49 mg, 0.40 mmol), and pyridine (40.2 µL, 0.50
mmol) in CH2Cl2 (35 mL) was stirred at room temperature for
24 h. After the solvent was evaporated in vacuo, toluene (10
mL) and 4 N HCl/EtOAc (0.2 mL) were added to dissolve the
solid residue, and the solution was stirred at room temperature
for 30 min. The mixture was extracted with a mixed solvent
of toluene and ethyl acetate (9:1 (v/v)) (3 times), dried over
MgSO4, and concentrated in vacuo. The residue was chromato-
graphed on silica gel (toluene) to give 4 as a brown powder
(36 mg, 76%). 1H NMR (500 MHz, CDCl3) 4-A δ 8.82 (1H, d, J
) 4.6 Hz, pyridine R-proton), 8.29 (2H, d, J ) 7.3 Hz), 8.01
(1H, d, J ) 7.0 Hz, pyridine γ-proton), 7.84 (1H, s), 7.63-7.39
(4H, m, aromatic), 5.59 (1H, d, J ) 14.0 Hz), 4.51 (1H, d, J )
14.0 Hz). 4-E δ 8.71 (1H, d, J ) 5.5 Hz, pyridine R-proton),
8.17 (2H, d, J ) 7.3 Hz), 7.97 (1H, d, J ) 7.3 Hz, pyridine
γ-proton), 7.68 (1H, s), 7.63-7.39 (4H, m, aromatic), 5.00 (1H,
d, J ) 14.2 Hz), 4.58 (1H, d, J ) 14.2 Hz); APCI MS m/z 945
(M+).
Spectroscopic data of 2b, e, f, i, k , and m are as follows.
2b: 1H NMR (500 MHz, CDCl3/CS2) δ 7.95 (1H, d, J ) 6.1
Hz), 7.70-7.60 (3H, m), 6.56 (1H, d, J ) 7.0 Hz), 4.66 (1H, q,
J ) 6.7 Hz), 3.27 (1H, d, J ) 7.0 Hz, OH), 2.31 (3H, d, J ) 6.7
Hz); FAB MS m/z 854 (M+).
2e: 1H NMR (500 MHz, CDCl3/CS2) 2e-A δ 7.85 (1H, d, J )
7.5 Hz), 7.70-7.54 (3H, m), 5.85 (1H, d, J ) 13.8 Hz), 4.35
(1H, d, J ) 13.7 Hz), 2.84 (1H, s, OH), 2.71 (3H, s, CH3). 2e-E
δ 8.05 (1H, d, J ) 8.2 Hz), 7.70-7.54 (3H, m), 5.08 (1H, d, J
) 15.0 Hz), 4.50 (1H, d, J ) 14.9 Hz), 3.01 (1H, s, OH), 2.62
(3H, s, CH3); FAB MS m/z 854 (M+).
2f: 1H NMR (500 MHz, CDCl3/CS2) 2f-A δ 8.20-7.10 (9H,
m), 5.85 (1H, d, J ) 14.0 Hz), 4.56 (1H, d, J ) 14.1 Hz), 3.12
(1H, s, OH). 2f-E δ 8.20-7.10 (9H, m), 5.04 (1H, d, J ) 14.3
Hz), 4.26 (1H, d, J ) 13.7 Hz), 3.41 (1H, s, OH); FAB MS m/z
916 (M+).
2i: 1H NMR (500 MHz, CDCl3/CS2) δ 7.54 (1H, d, J ) 7.0
Hz), 7.50 (1H, d, J ) 7.7 Hz), 7.39 (1H, d, J ) 7.7 Hz), 6.71
(1H, s), 5.61 (1H, d, J ) 13.4 Hz), 4.32 (1H, d, J ) 13.8 Hz),
3.09 (1H, s, OH), 2.66 (3H, s, CH3); FAB MS m/z 854 (M+).
2k : 1H NMR (500 MHz, CDCl3/CS2) 2k -A δ 7.61 (1H, d, J
) 7.9 Hz), 7.16 (1H, d, J ) 2.4 Hz), 6.98 (1H, dd, J ) 7.9, 2.3
Hz), 6.32 (1H, d, J ) 1.8 Hz), 5.57 (1H, d, J ) 13.7 Hz), 5.10
(1H, s, ArOH), 4.28 (1H, d, J ) 13.8 Hz), 3.12 (1H, d, J ) 1.8
Hz, aliphatic OH). 2k -E δ 7.80 (1H, d, J ) 8.2 Hz), 7.18 (1H,
d, J ) 2.1 Hz), 7.08 (1H, dd, J ) 8.5, 2.1 Hz), 6.45 (1H, d, J )
7.0 Hz), 5.00 (1H, s, ArOH), 4.76 (1H, d, J ) 14.0 Hz), 4.40
(1H, d, J ) 14.3 Hz), 3.26 (1H, d, J ) 7.0 Hz, aliphatic OH);
FAB MS m/z 856 (M+).
P r ep a r a tion of Ester 5. 5 was prepared in 70% yield (28
mg) by a procedure similar to that used for 4, using 2m (34
mg, 0.040 mmol), 1-naphthoyl chloride (48.0 µL, 0.40 mmol),
4-(dimethylamino)pyridine (39 mg, 0.32 mmol), and pyridine
1
(32.2 µL, 0.40 mmol). H NMR (500 MHz, CDCl3) 5-A δ 9.10
(1H, d, J ) 3.6 Hz), 8.86 (1H, d, J ) 4.6 Hz, pyridine R-proton),
8.62 (1H, d, J ) 6.7 Hz), 8.08-7.42 (7H, m, aromatic), 8.00
(1H, s), 5.59 (1H, d, J ) 14.2 Hz), 4.49 (1H, d, J ) 14.2 Hz).
5-E δ 9.09 (1H, d, J ) 3.7 Hz), 8.75 (1H, d, J ) 4.6 Hz, pyridine
R-proton), 8.50 (1H, d, J ) 7.0 Hz), 8.08-7.42 (7H, m,
aromatic), 7.81 (1H, s), 5.04 (1H, d, J ) 14.2 Hz), 4.60 (1H, d,
J ) 14.2 Hz); APCI MS m/z 995 (M+).
2m : 1H NMR (500 MHz, CDCl3/CS2) δ 8.82 (1H, d, J ) 5.2
Hz), 8.06 (1H, d, J ) 7.3 Hz), 7.61 (1H, m), 6.45 (1H, d, J )
4.6 Hz), 5.81 (1H, d, J ) 4.9 Hz, OH), 4.86 (1H, d, J ) 13.9
Hz), 4.53 (1H, d, J ) 14.1 Hz); 13C NMR (125 MHz, CDCl3/
CS2) δ 156.60, 156.30, 155.13, 154.37, 151.54, 148.78, 147.74,
147.68, 147.53, 147.48, 146.57, 146.50, 146.46, 146.31, 146.23,
146.17, 146.14, 145.84, 145.63, 145.57, 145.48, 145.43, 145.33,
P r ep a r a t ion of E st er 6. A mixture of 2m (84 mg, 0.10
mmol), 9-anthroic acid (67 mg, 0.30 mmol), DCC (62 mg, 0.30
mmol), and DMAP (12 mg, 0.10 mmol) was refluxed in dry
toluene (50 mL) for 5 days. The reaction mixture was chro-
matographed on silica gel (toluene) and further purified by
GPC (chloroform) to give 6 as a brown powder (49 mg, 47%).
1H NMR (500 MHz, CDCl3) 6-A δ 5.25 (1H, d, J ) 14.1 Hz),
4.29 (1H, d, J ) 13.7 Hz). 6-E δ 5.12 (1H, d, J ) 14.1 Hz),
4.66 (1H, d, J ) 13.7 Hz) (The peaks corresponding to the
cyclohexene methine (R1) proton and a total of 12 protons of
the pyridine and anthracene moieties were observed in the
region δ 9.0-7.4.); APCI MS m/z 1045 (M+).
(17) Klouwen, M. H.; Boelens, H. Recl. Trav. Chim. Pays-Bas 1960,
79, 1022.
(18) Wang, W.; Li, T.; Attardo, G. J . Org. Chem. 1997, 62, 6598.
(19) Comins, D. L.; Brown, J . D.; Mantlo, N. B. Tetrahedron Lett.
1982, 23, 3979.
(20) Ginsburg, S.; Wilson, I. B. J . Am. Chem. Soc. 1957, 79, 481.
(21) (a) Evans, E. A. Chem. Ind. (London) 1957, 1596. (b) Iversen,
P. E.; Lund, H. Acta Chem. Scand. 1966, 20, 2649. (c) Voss, G.; Gerlach,
H. Chem. Ber. 1989, 122, 1199.
Ack n ow led gm en t. This work was financially sup-
ported by the J apan Society for the Promotion of
Science.
(22) Anselmino, O. Chem. Ber. 1902, 35, 4108.
(23) Gross, H.; Rieche, A.; Matthey, G. Chem. Ber. 1963, 96, 308.
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