Isolation and characterization of nine tris-adducts of N- methylfulleropyrrolidine derivatives

Article abstract of DOI:10.1021/jo050417t

We report the isolation and characterization of bis- and tris-adducts of fulleropyrrolidine derivatives. First, all eight N-methyl regioisomers with two addends on the C₆₀ sphere have been isolated; second, C₆₀ was used as starting m

Full text of DOI:10.1021/jo050417t

Isolation and Characterization of Nine Tris-adducts of
N-Methylfulleropyrrolidine Derivatives
Silvia Marchesan, Tatiana Da Ros, and Maurizio Prato*
Dipartimento di Scienze Farmaceutiche, Universita` degli Studi di Trieste,
Piazzale Europa 1, 34127 Trieste, Italy
prato@units.it
Received March 4, 2005
We report the isolation and characterization of bis- and tris-adducts of fulleropyrrolidine derivatives.
First, all eight N-methyl regioisomers with two addends on the C60 sphere have been isolated;
second, C60 was used as starting material for the synthesis of tris-adducts, and the products formed
in detectable quantities have been isolated and characterized. Third, the same compounds were
obtained by introducing the third addend on each previously isolated bis-derivative: this approach
facilitated the assignment of the relative geometry through chromatographic comparison of the
diverse reaction mixtures. Finally, the obtained tris-adducts have been characterized by means of
ES-MS, UV-vis, 1H NMR, as well as comparison with UV spectra and elution order of Bingel and
Diels-Alder tris-adducts described in the literature.
Introduction
During the last 15 years, the chemistry of fullerene
has developed at a fast pace.1-4 In the initial period, the
researchers explored the chemical reactivity of the third
allotropic form of carbon; later, attention focused on the
synthesis of new derivatives to study the electrochemi-
cal,5,6 spectroscopic,7-10 and biological11-14 properties of
FIGURE 1. Tris-adduct C3 (equatorial, equatorial, equatorial)
and D3 (trans-3, trans-3, trans-3).
* To whom correspondence should be addressed. Phone: +39 040
558 7883. Fax: +39 040 5257.
fullerene and the possibility to modulate these charac-
teristics and their exploitation in medical and material
science.15,16 The cycloaddition reactions have been widely
used for these purposes,17,18 while new reactions continue
to be reported.19
At the beginning, the research was centered on the
monofunctionalization of the fullerene and, only later, on
the multiple additions, which cause the formation of
several regioisomers. The pioneering work to stere-
ochemically define multiple derivatives has been devel-
oped by Hirsch and co-workers, who undertook the first
extensive work on the isolation and characterization of
multiple adducts of C60 and reported the first tris-
adducts, the so-called C3 and D3 (Figure 1),20 widely used
for biomedical purposes.21-26
(1) Hirsch, A. The Chemistry of the Fullerenes; Thieme: Stuttgart,
1994.
(2) Taylor, R. The Chemistry of Fullerenes; World Scientific: Sin-
gapore, 1995.
(3) Hirsch, A. Top. Curr. Chem. 1999, 199, 1-65.
(4) Wilson, S.; Schuster, D.; Maggini, M.; Prato, M.; Taylor, R. In
Fullerenes: Chemistry, Physics, and Technology; Kadish, K., Ruoff, R.,
Ed.; Wiley: New York, 2000; pp 91-176.
(5) Kessinger, R.; Gomez-Lopez, M.; Boudon, C.; Gisselbrecht,
J.-P.; Gross, M.; Echegoyen, L.; Diederich, F. J. Am. Chem. Soc. 1998,
120, 8545-8546.
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goyen, L.; Diederich, F. Angew. Chem., Int. Ed. 1998, 37, 1919-1922.
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12896-12901.
(9) Nakamura, Y.; Taki, M.; Tobita, S.; Shizuka, H.; Yokoi, H.;
Ishiguro, K.; Sawaki, Y.; Nishimura, J. J. Chem. Soc., Perkin Trans.
2 1999, 127-130.
(10) Kordatos, K.; Da Ros, T.; Prato, M.; Leach, S.; Land, E.;
Bensasson, R. Chem. Phys. Lett. 2001, 334, 221-228.
(11) Bosi, S.; Da Ros, T.; Spalluto, G.; Prato, M. Eur. J. Med. Chem.
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10.1021/jo050417t CCC: $30.25 © 2005 American Chemical Society
Published on Web 05/12/2005
4706
J. Org. Chem. 2005, 70, 4706-4713

Synthesis of Fulleropyrrolidine Tris-adducts
SCHEME 1. Synthesis of Mono-, Bis-, and
Tris-fulleropyrrolidine Derivatives
Hirsch and collaborators clarified the addition pattern
of multiple cyclopropanation reactions. If two of the 30
double bonds of C60 are functionalized with a symmetrical
addend, there are eight possible bis-adducts. In particu-
lar, if the groups are not sterically demanding, all the
products can be observed;27-30 otherwise, only seven are
formed other than cis-1,31-34 although in the Bingel
reaction the second addition rather favors equatorial and
trans-3 bis-adducts. In a very elegant approach toward
the selective synthesis of polyadducts, different macro-
cyclic malonate addends were used to obtain the desired
bis- and tris-adducts.35 In the case of tris-adducts, in
which three 6-6 bonds have been functionalized, the
number of possible regioisomers increases to 46, still
considering a symmetrical addend; otherwise, the num-
ber of possible isomers is much higher. To date, a limited
amount of work20,31,35-43 has been carried out on such
compounds, due to the increased complexity of their
separation and characterization. In addition, most of the
research has dealt with either Bingel or Diels-Alder
reactions, mainly using tethers to direct the regioselec-
tivity.44 As a result, little is known on the relative yields
of tris-adduct formation without steric constrictions, in
particular using fullerene functionalization other than
cyclopropanation.
We have extensively studied the 1,3-dipolar cycload-
dition of azomethine ylides, yielding fulleropyrroli-
dines.18,45,46 This reaction presents a remarkably lower
selectivity compared to other cycloadditions, thus allow-
ing the formation of a higher number of isomers. More-
over, using the less sterically hindered reagents (HCHO
and N-Me-Gly) the possibility exists of formation of
isomers otherwise not observed (cis positions). Moreover,
this reaction gives bis- and tris-adducts, which are
coeluted in chromatography due to their extremely
similar polarity.8,27 This event adds more difficulties to
the isomer isolation and relative structural assignment.
However, we deemed it important to finally attribute the
structure to bis- and tris-fulleropyrrolidines, as these
molecules are increasingly used and show electronic
properties different from those of cyclopropano- and
aziridino-fused systems.47,48
(12) Nakamura, E.; Isobe, H. Acc. Chem. Res. 2003, 36, 807-815.
(13) Tagmatarchis, N.; Shinohara, H. Mini Rev. Med. Chem. 2001,
1, 339-348.
(14) Da Ros, T.; Prato, M. Chem. Commun. 1999, 663-669.
(15) Prato, M. Top. Curr. Chem. 1999, 199, 173-188.
(16) Prato, M. J. Mater. Chem. 1997, 7, 1097-1109.
(17) Bingel, K. Chem. Ber. 1993, 126, 1957-1959.
(18) Maggini, M.; Scorrano, G.; Prato, M. J. Am. Chem. Soc. 1993,
115, 9798-9799.
(19) Mart´ın, N.; Altable, M.; Filippone, S.; Mart´ın-Domenech, AÄ .
Chem. Commun. 2004, 1338-1339.
(20) Lamparth, I.; Hirsch, A. J. Chem. Soc., Chem. Commun. 1994,
1727-1728.
(21) Dugan, L. L.; Turetsky, D. M.; Du, C.; Lobner, D.; Wheeler,
M.; Almli, C. R.; Shen, C. K.-F.; Luh, T.-Y.; Choi, D. W.; Lin, T.-S.
Proc. Natl. Acad. Sci. U.S.A. 1997, 94, 9434-9439.
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FEBS Lett. 1999, 454, 335-340.
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M., Ruoff, R. S., Eds.; John Wiley & Sons: New York, 2000; pp 467-
479.
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W.; Monti, D.; Franceschi, C.; Schettini, G. J. Neurochem. 2000, 74,
1197-1204.
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D.; Wilson, S. Arch. Biochem. Biophys. 2000, 378, 216-223.
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Schoenberger, H.; Hirsch, A.; Moussa, F. J. Photochem. Photobiol. B
2002, 67, 157-162.
The main target of the present work is the exploration
of the regioselectivity in multiple additions, as well as
the investigation of the absorption spectroscopy, due to
the change in the conjugation of the π-electron cromo-
phore.49 We report for the first time the isolation and
characterization of nine fulleropyrrolidine tris-analogues,
three of which present an addition pattern never ob-
served before.
(27) Kordatos, K.; Bosi, S.; Da Ros, T.; Zambon, A.; Lucchini, V.;
Prato, M. J. Org. Chem. 2001, 66, 2802-2808.
(28) Nakamura, Y.; Takano, N.; Nishimura, T.; Yashima, E.; Sato,
M.; Kudo, T.; Nishimura, J. Org. Lett. 2001, 3, 1193-1196.
(29) Schick, G.; Hirsch, A.; Mauser, H.; Clark, T. Chem. Eur. J. 1996,
2, 935-943.
(30) Djojo, F.; Herzog, A.; Lamparth, I.; Hampel, F.; Hirsch, A. Chem.
Eur. J. 1996, 2, 1537-1547.
Results and Discussion
(31) Hirsch, A.; Lamparth, I.; Karfunkel, H. R. Angew. Chem., Int.
Ed. Engl. 1994, 33, 437-438.
The N-methylfulleropyrrolidine bis-adducts were syn-
thesized by reaction of 2 equiv of N-methylglycine (sar-
cosine), 1 equiv of C60, and 10 equiv of HCHO in refluxing
toluene for 1 h (Scheme 1).
(32) Nakamura, Y.; O-kawa, K.; Matsumoto, M.; Nishimura, J.
Tetrahedron 2000, 54, 5429-5434.
(33) Mas-Torrent, M.; Rodriguez-Mias, R. A.; Sol, M.; Molins, M. A.;
Pons, M.; Vidal-Gancedo, J.; Veciana, J.; Rovina, C. J. Org. Chem. 2002,
67, 566-575.
(34) Kreher, D.; Liu, S.-G.; Cariou, M.; Hudhomme, P.; Gorgues, A.;
Mas, M.; Veciana, J.; Rovira, C. Tetrahedron Lett. 2001, 42, 3447-
3450.
(41) Nierengarten, J.-F.; Habicher, T.; Kessinger, R.; Cardullo, F.;
Diederich, F.; Gramlich, V.; Gisselbrecht, J.-P.; Boudon, C.; Gross, M.
Helv. Chim. Acta 1997, 80, 2238-2276.
(42) Cardullo, F.; Seiler, P.; Isaacs, L.; Nierengarten, J.-F.; Haldimann,
R. F.; Diederich, F.; Mordasini-Denti, T.; Thiel, W.; Boudon, C.;
Gisselbrecht, J.-P.; Gross, M. Helv. Chim. Acta 1997, 80, 343-371.
(43) Hirsch, A.; Lamparth, I.; Gro¨sser, T.; Karfunkel, H. R. J. Am.
Chem. Soc. 1994, 116, 9385-9386.
(44) Isaacs, L.; Haldimann, R. F.; Diederich, F. Angew. Chem., Int.
Ed. Engl. 1994, 33, 2339-2342.
(45) Prato, M.; Maggini, M. Acc. Chem. Res. 1998, 31, 519-526.
(46) Tagmatarchis, N.; Prato, M. Synlett 2003, 768-779.
(47) Lu, Q.; Schuster, D. I.; Wilson, S. R. J. Org. Chem. 1996, 61,
4764-4768.
(35) Reuther, U.; Brandmuller, T.; Donaubauer, W.; Hampel, F.;
Hirsch, A. Chem. Eur. J. 2002, 8, 2261-2273.
(36) Rapenne, G.; Crassous, J.; Collet, A.; Echegoyen, L.; F., D.
Chem. Commun. 1999, 1121-1122.
(37) Rapenne, G.; Crassous, J.; Collet, A.; Echegoyen, L. E.; Eche-
goyen, L.; Flapan, E.; F., D. Helv. Chim. Acta 2000, 83, 1209-1223.
(38) Djojo, F.; Hirsch, A.; Grimme, S. Eur. J. Org. Chem. 1999,
3027-3039.
(39) Qian, W.; Rubin, Y. Angew. Chem., Int. Ed. 1999, 38, 2356-
2360.
(40) Isaacs, L.; Diederich, F.; Haldimann, R. F. Helv. Chim. Acta
1997, 80, 317-342.
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Marchesan et al.
which are diagnostic for the addition pattern, were
identical to those observed for analogue addition pat-
terns, in particular for C60 derivatives with five- and six-
membered rings.27,50,51 The number and intensities of the
1H and 13C NMR signals, as well as the elution order,
were compatible with the assigned structure symmetry.
Since there has been no systematic study of the
structure of bis-adducts of N-methylfulleropyrrolidine, we
1
discuss briefly their structural assignments. In its H
NMR spectrum, compound 1a displays one singlet at 4.68
ppm for the eight pyrrolidine protons and one singlet at
3.15 ppm for the two methyl groups, consistent with the
D2h symmetry of the trans-1 isomer, as confirmed by the
peculiar UV-vis absorption pattern and by the elution
order, as reported in the literature.8,27,47 Compounds 1b
FIGURE 2. HPLC chromatogram of the bis-addition reaction,
after 30 min, registered at 320 nm (method A, see the
Experimental Section).
1
and 1c show H NMR spectra, 13C NMR spectra, UV-
vis absorption pattern, and elution order in agreement
with the geometry assigned to isomers trans-2 and trans-
3, respectively.
The reaction was followed by HPLC, equipped with a
diode array detector, which allows UV-vis spectra
comparisons. After 30 min, the chromatogram presented
one peak for the monoadduct, seven peaks corresponding,
respectively, to the isomers trans-1, trans-2, trans-3, cis-
1, trans-4, equatorial, cis-2 (named 1a-g following the
elution order), and tris-adducts in traces (Figure 2).
After 1 h, the reaction mixture appeared too complex
to allow the assignment of each peak: electrospray mass
spectrometry (ES-MS) analysis revealed the formation
of various tris-adducts. In addition, as previously ob-
served,27 it was not possible to identify the peak corre-
sponding to the cis-3 (1h), even if the compound was
eventually obtained after tedious chromatographic sepa-
rations. In fact, some isomers have extremely similar
polarities: repeated HPLC analysis revealed the coelu-
tion of different bis- and tris-adducts combined under the
same peak. In certain cases, the UV-vis spectra of the
coeluted compounds were similar, so that ES-MS analysis
proved essential to unambiguously assign the number of
adducts (Figure 3).
Compound 1f is the only bis-adduct possessing a vivid
red color. Its 13C NMR spectrum is the only one consistent
with the Cs symmetry of an equatorial structure, display-
ing 27 peaks integrating two carbons each and two peaks
integrating one carbon each between 135 and 159 ppm.
This isomer is also characterized by the relative 90°
orientation of the two pyrrolidines, which are nonequiva-
1
lent and in H NMR display one multiplet at 4.01 ppm
integrating six protons and one broad singlet at 3.87 ppm
integrating 2H; finally, the six nonequivalent methyl
protons resonate at 2.80 ppm. The UV-vis absorption
pattern and elution order are in agreement with the
equatorial N-mTEG-fulleropyrrolidine previously char-
acterized.27 The elution order and the relative yield of 1f
are also consistent with equatorial attribution.
The isomer 1h presents a 13C NMR spectrum with 28
signals integrating two carbons each, reflecting C2 symme-
try, displayed by trans-2, trans-3, and cis-3 isomers. Since
the first two have been already identified, the only isomer
consistent with the data is the cis-3. Indeed, visible spec-
tra comparisons with the cis-3 reported by Nishimura48
corroborate this assignment. Notably, the 1H NMR
signals are shifted downfield with respect to the trans-2
and trans-3 isomers, displaying two doublets at 4.21 and
3.99 ppm and other two doublets at 3.99 and 3.93 ppm.
The NMR spectra of the last three compounds (1d, 1e,
and 1g) display Cs symmetry as expected for cis-1, trans-
All the N-methylfulleropyrrolidine bis-adducts were
separated by repeated medium-pressure column chro-
matography, preparative TLC, and further purification
by semipreparative HPLC. The eight isomers were
isolated and fully characterized by ES-MS, UV-vis, and
1H and 13C NMR and are in accordance with the previ-
ously reported data.8,48 The UV-vis absorption profiles,
FIGURE 3. UV-vis spectra of compound bis-1g (cis-2) and tris-2g (trans-3, trans-4, equatorial).
4708 J. Org. Chem., Vol. 70, No. 12, 2005

Synthesis of Fulleropyrrolidine Tris-adducts
4, and cis-2. The most abundant is 1e, which is charac-
terized by an olive green color, in contrast with the
brown-orange color generally displayed by the other
adducts. Visible spectra comparisons clearly indicate a
trans-4 geometry: the absorption pattern and elution
order are identical to the analogue N-mTEG-bis-fullero-
pyrrolidine. Isomers 1d and 1g also show visible spectra
and elution order identical to the N-mTEG-bis-fullero-
pyrrolidines cis-1 and cis-2, respectively.14 The extremely
low yield of 1d is typical of cis-1, if we consider that this
isomer is the least favored due to steric repulsion between
addends.
The 1,3-dipolar cycloaddition of azomethine ylides
leads to the formation of not only all the eight possible
bis-adducts but also of many tris-derivatives, whose
isolation and characterization represent an impressive
challenge. If, on one hand, the systematic investigation
of bis-addition regioselectivity has been extensively
pursued, no work has been carried out on tris-fulleropy-
rrolidines. The only tris-pyrrolidine derivative isolated
so far (trans-3, trans-3, trans-3) has been reported by
Rubin and collaborators.52
FIGURE 4. HPLC chromatogram of the tris-addition reaction,
registered at 320 nm (method B, see the Experimental Sec-
tion).
The reaction of C60 with 3 equiv of N-methylglycine
and an excess of HCHO in refluxing toluene was followed
by HPLC: the crude was very complex, and at least 17
products (bis- and tris-adducts) were detected. We pro-
ceeded with the chromatographic separations using
repeated columns and preparative TLC in silica gel and
eluant mixtures of toluene/ethyl acetate. Nine isomers
(named 2a-i after the elution order) were purified, and
ES-MS analysis corroborated that all the molecules are
N-methylfulleropyrrolidine tris-adducts (Figure 4).
Next, we heated each bis-adduct with 1 equiv of
N-methylglycine and an excess of HCHO in toluene. The
reactions proceeded with difficulty compared to reaction
with C60. Nonetheless, due to the reduced material
availability, the bis-isomers trans-1, cis-1, and cis-3 did
not allow the identification of their relative addition tris-
products. However, a thorough study of the chromato-
grams related to the other isomer additions (Figure 5),
paying particular attention to the peaks which presented
identical retention times and UV-vis spectra in the 400-
800 nm range, allowed a first partial assignment of the
addition patterns of compounds 2a-i.
Compound 2a exhibits a cherry red color and can be
easily recognized as the trans-3, trans-3, trans-3 already
reported by Rubin.52 The high symmetry of the compound
(D3) is reflected in its NMR spectra. The protons give two
singlets, one at 2.85 ppm for the equivalent methyl
groups and one broad at 4.06 ppm for the pyrrolidine
protons. The C60 sp2 carbons give only nine signals
between 160 and 140 ppm, the sp3 fullerene and pyrro-
lidine carbons give two signals at 69.40 and 69.20 ppm,
and finally the equivalent methyl groups resonate at
42.36 ppm. This isomer is one of the first tris isomers to
be formed and shows an extremely similar polarity to the
trans-4 isomer, which can be easily distinguished by
sight, the first being cherry red and the second olive
green.
The approach adopted in the present work includes,
first, the synthesis and isolation of the bis-adducts using
C
60 as starting material and, second, the introduction of
the third group on each previously purified bis-derivative.
This has been revealed to be crucial for the geometry
assignment, since the reaction is irreversible and thus
the positional relationships among addends present in
the bis-adduct are preserved in any tris-derived. The
addition pattern of the products has been deduced on the
basis of the precursor known geometry and verified via
analysis of the NMR spectra, which reflect the symmetry
of the compounds. In fact, in this sense, there are three
possible cases: adducts with all the addends in the same
relative position (e.g., trans-3, trans-3, trans-3) which
present a 3-fold symmetry; adducts with two addends in
the same relative position (e.g., trans-3, trans-3, trans-
4) which possess a 2-fold symmetry; and, finally, asym-
metrical adducts with the addends in three different
positional relationships (e.g., trans-3, trans-4, equatorial).
Furthermore, when possible, the data obtained were
further verified via comparison of the UV-vis spectra
and elution order of Bingel or Diels-Alder tris-deriva-
tives.
The nomenclature of tris-adducts has been adopted
from Hirsch et al.31 Basically, if we call the three addends
1, 2, and 3, the first sterochemical relationship is between
1 and 2, the second between 2 and 3, and the third is
between 3 and 1. For example, trans-3, trans-4, equatorial
means that addend 1 and 2 are in trans-3 relation, 2 and
3 in trans-4 relation, and 1 and 3 in equatorial relation.
(48) While the present work was already completed, a thorough
investigation of formation of N-methyl-bis-pyrrolidines has appeared:
Nishimura, T.; Tsuchiya, K.; Ohsawa, S.; Maeda, K.; Yashima, E.;
Nakamura, Y.; Nishimura, J. J. Am. Chem. Soc. 2004, 126, 11711-
11717.
(49) Boudon, C.; Gisselbrecht, J.-P.; Gross, M.; Isaacs, L.; Anderson,
H. L.; Faust, R.; Diederich, F. Helv. Chim. Acta 1995, 78, 1334-1344.
(50) Taki, M.; Sugita, S.; Nakamura, Y.; Kasashima, E.; Yashima,
E.; Okamoto, Y.; Nishimura, J. J. Am. Chem. Soc. 1997, 119, 926-32.
(51) Da Ros, T.; Prato, M.; Lucchini, V. J. Org. Chem. 2000, 65,
4289-4297.
(52) Schick, G.; Levitus, M.; Kvetko, L.; Johnson, B. A.; Lamparth,
I.; Lunkwitz, R.; Ma, B.; Khan, S. I.; Garcia-Garibay, M. A.; Rubin, Y.
J. Am. Chem. Soc. 1999, 121, 3246-3247.
Compound 2b also shows a vivid red color and was
found in the addition reactions carried out on the trans-3
and trans-4 isomers; thus, two addition patterns are
1
known. The H NMR spectrum highlights a simplicity
due to the presence of one plane of symmetry: there are
three AB systems (dd) for the pyrrolidines and two
J. Org. Chem, Vol. 70, No. 12, 2005 4709

Marchesan et al.
FIGURE 5. HLPC chromatograms of tris-addition on each bis-adduct, registered at 320 nm (program B, see Experimental Section).
§The peak, attributed to 1g, also contains two tris-adducts which are not completed identified. They present, respectively, the
equatorial and cis-2 geometries the first and the trans-3 and cis-2 geometries the second, but it was not possible to identified the
third addition pattern.
singlets for the methyl groups. The only compatible
geometry is trans-3, trans-3, trans-4, confirmed via
comparison with elution order and UV-vis spectrum of
the analogue Bingel derivative (Figure 6).38
Compound 2c is olive green and was found in the
reaction mixtures of trans-2 and trans-4. In this case, the
1H NMR spectrum also reflects the presence of an
element of symmetry, being very similar to that of
compound 2b. The only possible addition pattern is trans-
2, trans-4, trans-4, in accordance with the data related
to the corresponding Bingel tris-adduct.38
by the tris-adducts displaying a cis-2 addition pattern
(approximately 10% each). This result is not very sur-
prising if we consider that the azomethine ylide 1,3-
dipolar cycloaddition is less chemoselective compared to
cyclopropanation, as already reported.47 Furthermore, it
is well-known that addends on the cis-2 position are
favored by the HOMO-LUMO coefficients, but such
derivatives are not generally recovered if the groups are
sterically demanding: the choice for small molecules such
as HCHO and N-methylglycine for our study proved
essential for their isolation.
Compounds 2d, 2e, and 2g are brown-orange and were
found in the crudes of trans-2, trans-3, equatorial; trans-
2, trans-4, equatorial; and trans-3, trans-4, equatorial,
Conclusions
N-Methylfulleropyrrolidine bis-adducts constitute a
series of isomers whose polarity is extremely similar, as
the groups introduced on the C60 sphere are small and
do not display particularly polar functional groups. Their
separation is a task also complicated by other factors,
mainly the coformation and coelution of diverse tris-
adducts. Here, we have reported the isolation and
characterization of the complete series. Higher adducts
have become a topic of great interest, and until now, all
of the work conducted on tris-derivatives has concen-
trated on Bingel or Diels-Alder functionalizations. For
the first time, nine fulleropyrrolidine tris-adducts have
been purified and unambiguously characterized, includ-
ing three isomers (trans-2, trans-3, cis-2; trans-2, trans-
4, cis-2; and trans-2, equatorial, cis-2) which possess an
addition pattern never described before for fullerene
adducts. The most abundant product is the asymmetrical
trans-2, trans-3, equatorial, in accordance with the
diverse regioselectivity already noticed for the azome-
thine ylide 1,3-dipolar cycloaddition compared to cyclo-
propanation.47
1
respectively; thus, their geometries are known. The H
NMR spectra reflect their asymmetry, showing all six AB
systems for the pyrrolidine protons and the three singlets
for the methyl groups. The elution order and UV-vis
spectra of 2d, 2e, and 2g were compatible with the
corresponding tris-malonates known in the literature.38
Surprisingly, in contrast to the cyclopropanation reaction,
compound 2d is the most favored isomer, the only one
formed in sufficient quantities to allow 13C NMR analysis,
which shows all 54 signals of the C60 sp2 carbons as well
as the 15 fullerene and pyrrolidine sp3 carbons.
Compounds 2f, 2h, and 2i are brown and were im-
mediately identified as the isomers trans-2, trans-3, cis-
2; trans-2, trans-4, cis-2; and trans-2, equatorial, cis-2.
Their asymmetry is confirmed by their 1H NMR spectra,
where the 6 AB systems and the three methyl singlets
can be distinguished.
The relative yields of the tris-adducts clearly indicate
the favored formation of trans-2, trans-3, equatorial
(27%), followed by trans-3, trans-4, equatorial (13%), and
4710 J. Org. Chem., Vol. 70, No. 12, 2005

Synthesis of Fulleropyrrolidine Tris-adducts
FIGURE 6. Tris-adduct models and UV-vis spectra.
Retention time: monoadduct, 23 min; trans-1, 30 min;
trans-2, 31 min; trans-3, 32 min; cis-1, 34 min; trans-3, trans-
3, trans-3, 35 min; trans-4, 38 min; equatorial, 53 min; cis-2
and cis-3, 66 min. The solution was concentrated under
reduced pressure, and bis- and tris-adducts were purified from
unreacted C60 and monoadduct by medium-pressure column
chromatography on silica gel (0.063-0.200 mm), eluting with
toluene. C60 and the monoadduct are precipitated by CS2/
MeOH and dried under vacuum. The monoadduct (0.49 g, 0.63
mmol) was then dissolved in 250 mL of toluene with N-
methylglycine (56.3 mg, 0.63 mmol) and formaldehyde (37.9
mg, 1.26 mmol). The reaction was followed by HPLC using
the previously reported program A. All the bis- and tris-
adducts were separated by medium-pressure column chroma-
tography on fine silica gel (0.015-0.04 mm), eluting with
toluene/petroleum ether 4/1, toluene, then toluene/ethyl ac-
etate, and finally toluene/methanol. Bis-adducts trans-1, trans-
2, trans-3, and cis-1 eluted with toluene/petroleum ether 4/1;
trans-4 and the tris trans-3, trans-3, trans-3 eluted with
toluene/ethyl acetate 9/1; bis-adducts equatorial, cis-2, cis-3
eluted with toluene/ethyl acetate 85/15; finally, higher adducts
elute with toluene/methanol 1/1. Bis-adducts trans-1, trans-
2, trans-3, and cis-1 were separated through a medium-
pressure column chromatography on fine silica gel (0.015-
0.04 mm), using a mixture of toluene/ethyl acetate 99/1. The
impure fractions were further separated by semipreparative
HPLC eluting with toluene/ethyl acetate 85/15 (tR: trans-1,
22 min; trans-2, 24 min; trans-3, 28 min; cis-1, 29 min). Bis-
adduct trans-4 (green) was separated from tris-adduct trans-
Visible spectra comparisons were a very useful tool for
addition pattern assignment, and the absorption profiles
in the range of 400-800 nm have proved to be indepen-
dent from the nature of the addend and distinctive of the
geometry of each isomer, as long as the C60 derivatives
present five- or six-membered rings. Therefore, we sug-
gest the use of the UV-vis spectra of the tris-pyrrolidines
(Figure 6) as a reference for future geometry attribution
on tris-adducts presenting five- or six-membered rings.
Experimental Section
Materials and Methods. To record electrospray mass
spectra, compounds were dissolved in THF/MeOH 1/1 solutions
unless otherwise noted. The NMR spectra have been recorded
in CDCl3 solutions, unless otherwise stated. TMS has been
used as internal standard, and chemical shifts are given in
parts per million (ppm) relative to that of tetramethylsilane.
The HPLC analysis was conducted with a Phenomenex Pro-
digy 5 µm silica 100 Å column for the direct-phase purifications.
Synthesis of N-Methyl-bis-fulleropyrrolidines. A solu-
tion of 1.00 g of C60 (1.38 mmol), 0.25 g of N-methylglycine
(2.78 mmol), and 0.21 g of formaldehyde (6.94 mmol) in 700
mL of toluene was heated to reflux for 1 h. The reaction was
followed by HPLC, using the following elution program A: t
) 0 min, toluene 100%, flow 0 mL/min; t ) 3 min, toluene
100%, flow 1 mL/min; t ) 33 min, toluene/ethyl acetate 1/4,
flow 1 mL/min; t ) 83 min, toluene 100%, flow 1 mL/min; t )
86 min, toluene 100%, flow 0 mL/min
J. Org. Chem, Vol. 70, No. 12, 2005 4711

Marchesan et al.
1
3, trans-3, trans-3 (cherry red) by a preparative TLC in CH2Cl2.
The fractions with the equatorial and cis-2 were separated by
repeated column chromatography on fine silica gel (0.015-
0.04 mm) eluting first with 100% toluene and then adding
ethyl acetate until reaching 10%. Finally, cis-3 isomer (reten-
tion time 25 min) was separated by semipreparative HPLC
using the following eluting program with a constant flow of 1
mL/min: t ) 0 min, toluene/2-propanol 49/1; t ) 10 min,
toluene/2-propanol 49/1; t ) 11 min, toluene/2-propanol 9/1; t
) 26 min, toluene/2-propanol 9/1; t ) 27 min, toluene/2-
propanol 49/1.
m/z 835 (MH+); H NMR (200 MHz) δ 3.93 (m, 4H), 3.77 (m,
4H), 2.78 (s, 6H); UV-vis (cyclohexane) λmax 241, 256, 316, 446,
712, 743.
1h: cis-3 N-methyl-bis-fulleropyrrolidine; C66H14N2 (MW
834.852); relative yield 1.4% (2 mg, 0.0024 mmol); ES-MS m/z
835 (MH+); 1H NMR (200 MHz) δ 4.21 (d, J ) 9.2 Hz, 2H),
3.99 (d, J ) 9.5 Hz, 2H), 3.99 (d, J ) 9.5 Hz, 2H), 3.93 (d, J )
9.5 Hz, 2H), 2.85 (s, 6H); 13C NMR (50 MHz) δ 151.8 (2C), 149.7
(2C), 149.0 (2C), 148.5 (2C), 148.3 (2C), 148.0 (2C), 147.5 (2C),
146.9 (2C), 146.2 (2C), 145.9 (2C), 145.7 (2C), 145.4 (2C), 145.4
(2C), 145.4 (2C), 145.1 (2C), 145.0 (2C), 144.7 (2C), 142.1 (2C),
142.1 (2C), 141.8 (2C), 141.7 (2C), 141.3 (2C), 139.7 (2C), 138.5
(2C), 136.7 (2C), 135.0 (2C), 134.0 (2C), 130.3 (2C), 71.4 (2C),
69.9 (2C), 69.8 (2C), 66.1 (2C), 41.5 (2C); UV-vis (cyclohexane)
λmax 241, 256 (sh), 316, 462, 560 (br), 654, 720.
Each bis-adduct was dissolved in CS2, precipitated with
acetone, washed with MeOH, and dried under vacuum.
1a: trans-1 N-methyl-bis-fulleropyrrolidine; C66H14N2 (MW
1
834.852); relative yield 0.6% (1.0 mg, 0.012 mmol); H NMR
Synthesis of N-Methyl-tris-fulleropyrrolidines. From
60. A solution of 1.00 g of C60 (1.38 mmol), 0.37 g of
(200 MHz, CDCl3/CS2) δ 4.68 (s, 8H), 3.15 (s, 6H); UV-vis
(cyclohexane) λmax 246, 330 (sh), 457, 491, 712, as reported by
Lu et al.47
C
N-methylglycine (4.17 mmol), and 0.42 g of formaldehyde (13.9
mmol) in 700 mL of toluene was heated to reflux for 1 h and
followed by TLC in toluene/ethyl acetate 4/1 as well by HPLC
(program A). The solution was concentrated under reduced
pressure, and bis- and tris-adducts were purified from unre-
acted C60 and monoadduct by medium-pressure column chro-
matography on silica gel, eluting with toluene. All the bis-
adducts were separated using the same methodology previously
described: due to the complexity of the isomers mixture, it is
necessary to separate the bis-adducts first. The cherry red 2a
(trans-3, trans-3, trans-3) was found in the fraction containing
the bis-isomer trans-4 (green) from which it can be separated
by preparative TLC in CH2Cl2. Compounds 2b (trans-3, trans-
3, trans-4), 2c (trans-2, trans-4, trans-4), and 2d (trans-2,
trans-3, equatorial) were contained in the same fraction as the
equatorial bis-adduct. They were separated by HPLC in
toluene/ethyl acetate 85/15 (tR: 2b, 46 min; 2c, 55 min; 2d,
59 min).
Compounds 2e (trans-2, trans-4, equatorial), 2f (trans-2,
trans-3, cis-2), 2g (trans-3, trans-4, equatorial), 2h (trans-2,
trans-4, cis-2), and 2i (trans-2, equatorial, cis-2) were eluted
together with bis-adducts cis-2 and cis-3. They were separated
by HPLC using the following eluting program B with a
constant flow of 1 mL/min: t ) 0 min, toluene/ethyl acetate
4/1; t ) 20 min, toluene/ethyl acetate 4/1; t ) 40 min, toluene/
ethyl acetate 7/3; t ) 52 min, toluene/ethyl acetate 4/1. tR: 2e,
29 min; 2f, 34 min; 2g, 38 min; 2h, 43 min; 2i, 46 min.
From N-Methyl-bis-fulleropyrrolidines. A solution of 10
mg of each N-methylfulleropyrrolidine bis-adduct (1.2‚10-2
mmol), 1.07 mg of N-methylglycine (1.2‚10-2 mmol), and 3.60
mg of formaldehyde (1.2‚10-1 mmol) in 5 mL of toluene (o-
dichlorobenzene for trans-1 and trans-2 isomers) was heated
to reflux overnight and followed by TLC in toluene/ethyl
acetate 4/1. The solution was concentrated under reduced
pressure, and tris-adducts were purified from unreacted bis-
adduct by medium-pressure column chromatography on fine
silica gel (0.015-0.040 mm), eluting with toluene/ethyl acetate
95/5. Both the fraction with the products and the fraction with
the unreacted bis-adduct were analyzed by HPLC using the
eluting program B. Retention times: 2a, 10 min; 2b, 17 min;
2c, 22 min; 2d, 23 min; 2e, 29 min; 2f, 34 min; 2g, 38 min;
2h, 43 min; 2i, 46 min. Equatorial and cis-2 bis-adducts were
eluted together with tris-adducts and therefore were separated
through careful repeated semipreparative HPLC.
1b: trans-2 N-methyl-bis-fulleropyrrolidine; C66H14N2 (MW
834.852); relative yield 24.4% (35 mg, 0.042 mmol); ES-MS
m/z 834 (M+), 417 (M2+); 1H NMR (200 MHz, CDCl3/CS2) δ
4.64 (d, J ) 9.2 Hz, 2H), 4.46 (d, J ) 8.8 Hz, 2H), 4.35 (d, J )
6.6 Hz, 2H), 4.30 (d, J ) 6.5 Hz, 2H), 3.05 (s, 6H); its low
solubility did not allow 13C NMR analysis; UV-vis (cyclohex-
ane) λmax 245, 262 (sh), 310 (sh), 428, 474, 650, 722.
1c: trans-3 N-methyl-bis-fulleropyrrolidine; C66H14N2 (MW
834.852); relative yield 18.5% (26 mg, 0.031 mmol); ES-MS
1
m/z 834 (M+); H NMR (200 MHz, CDCl3/CS2) δ 4.42 (d, J )
9.1 Hz, 2H), 4.33 (d, J ) 9.1 Hz, 2H), 4.17 (d, J ) 9.3 Hz, 2H),
4.07 (d, J ) 9.2 Hz, 2H), 2.94 (s, 6H); 13C NMR (50 MHz) δ
158.0 (2C), 155.5 (2C), 155.4 (2C), 154.7 (2C), 152.6 (2C), 149.0
(2C), 148.7 (2C), 148.6 (2C), 148.1 (2C), 148.1 (2C), 146.5 (2C),
145.2 (2C), 145.1 (2C), 145.0 (2C), 145.0 (2C), 144.8 (2C), 144.5
(2C), 143.6 (2C), 143.5 (2C), 142.4 (2C), 141.5 (2C), 141.3 (2C),
141.1 (2C), 140.9 (2C), 139.7 (2C), 138.4 (2C), 136.3 (2C), 135.4
(2C), 70.4 (2C), 70.1 (2C), 70.1 (2C), 69.2 (2C), 41.6 (2C); UV-
vis (cyclohexane): λmax 246, 411 (sh), 463, 486 (sh), 640 (br),
695.
1d: cis-1 N-methyl-bis-fulleropyrrolidine; C66H14N2 (MW
834.852); relative yield 0.6% (0.9 mg, 0.0011 mmol); ES-MS
m/z 834 (M+), 418 (MH+/2); 1H NMR (200 MHz, CDCl3/CS2) δ
4.22 (d, J ) 8.7 Hz, 4H), 4.03 (d, J ) 8.5 Hz, 2H), 3.61 (d, J )
9.8 Hz, 2H), 2.85 (s, 6H); UV-vis (cyclohexane) λmax 246, 330
(sh), 429, 648, 714. Its low yield did not give enough material
for 13C NMR analysis.
1e: trans-4 N-methyl-bis-fulleropyrrolidine; C66H14N2 (MW
834.852); relative yield 17.8% (25 mg, 0.030 mmol);. ES-MS
1
m/z 834 (M+); H NMR (200 MHz, CDCl3/CS2) δ 4.29 (d, J )
9.2 Hz, 2H), 4.16 (d, J ) 9.2 Hz, 2H), 4.08 (m, 4H), 2.88 (s,
6H); 13C NMR (50 MHz, CDCl3/CS2) δ 154.2 (2C), 152.3 (2C),
151.1 (2C), 150.6 (1C), 150.3 (2C), 149.4 (1C), 148.9 (2C), 148.0
(2C), 147.6 (2C), 147.3 (1C), 147.1 (2C), 146.0 (2C), 145.8 (4C),
145.3 (2C), 144.7 (2C), 144.7 (2C), 144.3 (2C), 143.1 (1C), 142.4
(2C), 141.9 (2C), 141.5 (2C), 141.5 (2C), 141.1 (2C), 141.0 (2C),
138.9 (2C), 138.4 (2C), 135.9 (2C), 135.2 (2C), 131.0 (2C), 70.0
(2C), 69.7 (2C), 69.5 (2C), 69.3 (2C), 41.4 (2C); UV-vis
(cyclohexane) λmax 225, 241, 265, 306, 411 (sh), 450, 639, 705.
1f: equatorial N-methyl-bis-fulleropyrrolidine; C66H14N2
(MW 834.852); relative yield 35.0% (50 mg, 0.060 mmol); ES-
1
MS m/z 835 (MH+); H NMR (200 MHz) δ 4.01 (m, 6H), 3.87
2a: N-methyl-tris-fulleropyrrolidine trans-3, trans-3, trans-
(s, 2H), 2.79 (s, 6H); 13C NMR (50 MHz) δ 158.7 (2C), 153.2
(2C), 152.7 (2C), 152.5 (2C), 149.6 (1C), 148.7 (2C), 147.9 (2C),
147.9 (1C), 147.5 (2C), 147.0 (2C), 147.0 (2C), 146.5 (2C), 146.4
(2C), 145.6 (2C), 145.0 (2C), 144.8 (2C), 144.5 (2C), 144.5 (2C),
144.2 (2C), 143.5 (2C), 143.1 (2C), 142.1 (2C), 141.6 (2C), 141.5
(2C), 141.3 (2C), 140.5 (2C), 139.0 (2C), 136.6 (2C), 135.4 (2C),
70.2 (2C), 69.9 (2C), 69.5 (2C), 69.0 (2C), 41.6 (1C), 41.4 (1C);
UV-vis (cyclohexane) λmax 241, 256 (sh), 316, 422, 440 (sh).
3; C69H21N3 (MW 891.956); relative yield 4.6% (2.7 mg, 0.003
mmol); ES-MS m/z 893 (MH+); H NMR (400 MHz) δ 4.06 (s,
1
12H), 2.85 (s, 9H); 13C NMR (50 MHz) δ 158.20 (6C), 155.9
(6C), 152.0 (6C), 149.3 (6C), 148.5 (6C), 144.4 (6C), 142.9 (6C),
140.5 (6C), 69.4 (6C), 69.2 (6C), 42.4 (3C); the low amount of
obtained compound did not allow recording of the 13C NMR
spectrum; UV-vis (CH2Cl2) λmax 225, 241, 265, 306, 440, 490
(br), 538.
1g: cis-2 N-methyl-bis-fulleropyrrolidine; C66H14N2 (MW
834.852); relative yield 1.7% (2.5 mg, 0.0030 mmol); ES-MS
2b: N-methyl-tris-fulleropyrrolidine trans-3, trans-3, trans-
4; C69H21N3 (MW 891.956); relative yield 5.5% (3.2 mg, 0.004
4712 J. Org. Chem., Vol. 70, No. 12, 2005

Synthesis of Fulleropyrrolidine Tris-adducts
1
mmol); ES-MS m/z 893 (MH+); H NMR (400 MHz) δ 4.22 (d,
2f: N-methyl-tris-fulleropyrrolidine trans-2, trans-3, cis-2;
C69H21N3 (MW 891.956); relative yield 10.2% (5.9 mg, 0.007
mmol); ES-MS m/z 893 (MH2+); 1H NMR (400 MHz) δ 4.51 (d,
J ) 11.7 Hz, 1H), 4.31 (d, J ) 9.8 Hz, 1H), 4.07 (m, 4H), 3.92
(m, 2H), 3.77 (d, J ) 11.7 Hz, 1H), 3.60 (m, 2H), 3.48 (d, J )
9.8 Hz, 1H), 2.94 (s, 3H), 2.78 (s, 3H), 2.70 (s, 3H); the low
amount of obtained compound did not allow recording of the
13C NMR spectrum; UV-vis (CH2Cl2) λmax 225, 241, 265, 306,
448, 649.
2g: N-methyl-tris-fulleropyrrolidine trans-3, trans-4, equa-
torial; C69H21N3 (MW 891.956); relative yield 13.4% (7.8 mg,
0.009 mmol); ES-MS m/z 893 (MH+); 1H NMR (400 MHz) δ
4.12 (m, 2H), 4.04 (m, 2H), 3.84 (m, 4H), 3.72 (m, 4H), 2.81 (s,
3H), 2.79 (s, 3H), 2.70 (s, 3H); the low amount of obtained
compound did not allow recording of the 13C NMR spectrum;
UV-vis (CH2Cl2) λmax 225, 241, 265, 307, 457 (br).
2H), 4.15 (d, 2H), 4.08 (d, 2H), 4.00 (d, 2H), 3.89 (m, 4H), 2.87
(s, 3H), 2.77(s, 6H); the low amount of obtained compound did
not allow recording of the 13C NMR spectrum; UV-vis (CH2Cl2)
λmax 225, 241, 265, 306, 475 (sh), 530, 572.
2c: N-methyl-tris-fulleropyrrolidine trans-2, trans-4, trans-
4; C69H21N3 (MW 891.956); relative yield 8.6% (5.0 mg, 0.006
1
mmol); ES-MS m/z 893 (MH+); H NMR (400 MHz) δ 4.28 (d,
J ) 8.8 Hz, 2H), 4.23 (d, J ) 13.2 Hz, 4H), 4.33 (d, J ) 8.8 Hz,
2H), 3.99 (d, J ) 10.9 Hz, 2H), 3.90 (d, J ) 10.9 Hz, 2H), 2.91
(s, 6H), 2.76 (s, 3H); the low amount of obtained compound
did not allow recording of the 13C NMR spectrum; UV-vis
(CH2Cl2) λmax 225, 241, 265, 306, 503, 591, 644.
2d: N-methyl-tris-fulleropyrrolidine trans-2, trans-3, equa-
torial; C69H21N3 (MW 891.956); relative yield 27.0% (15.7 mg,
0.018 mmol); ES-MS (THF-MeOH 1:1) m/z 893 (MH+); 1H
NMR (400 MHz) δ 4.38 (d, J ) 9.4 Hz, 1H), 4.32 (d, J ) 9.4
Hz, 1H), 4.31 (d, J ) 9.4 Hz, 1H), 4.19 (d, J ) 11.0 Hz, 1H),
4.10 (d, J ) 11.1 Hz, 1H), 4.01 (d, J ) 8.0 Hz, 1H), 3.92 (d, J
) 7.8 Hz, 1H), 3.89 (d, J ) 9.5 Hz, 1H), 3.85 (m, 2H), 3.80 (m,
2H), 2.96 (s, 3H), 2.81 (s, 3H), 2.73 (s, 3H); 13C NMR (50 MHz)
δ 161.5 (1C), 161.1 (1C), 159.5 (1C), 156.5 (1C), 156.1 (1C),
154.0 (1C), 153.2 (1C), 153.1 (1C), 152.6 (1C), 151.6 (1C), 151.5
(1C), 151.4 (1C), 151.0 (1C), 150.4 (1C), 150.2 (1C), 149.5 (1C),
149.1 (1C), 149.0 (1C), 148.8 (1C), 148.5 (1C), 148.3 (1C), 148.3
(1C), 148.0 (1C), 147.3 (1C), 147.1 (1C), 146.9 (1C), 146.4 (1C),
146.3 (1C), 146.0 (1C), 145.9 (1C), 145.7 (1C), 145.6 (1C), 145.0
(1C), 144.4 (1C), 144.1 (1C), 143.7 (1C), 143.7 (1C), 143.4 (1C),
142.7 (1C), 142.2 (1C), 141.8 (1C), 141.8 (1C), 141.5 (1C), 141.4
(1C), 141.2 (1C), 141.2 (1C), 140.8 (1C), 140.6 (1C), 140.3 (1C),
139.8 (1C), 139.7 (1C), 139.5 (1C), 133.5 (1C), 132.7 (1C), 70.0
(1C), 69.9 (1C), 69.9 (1C), 69.6 (1C), 69.5 (1C), 69.4 (1C), 69.1
(1C), 68.93 (1C), 69.0 (1C), 68.7 (1C), 68.4 (1C), 41.8 (1C), 41.7
(1C), 41.5 (1C); UV-vis (CH2Cl2) λmax 225, 241, 265, 306, 441,
475 (sh), 554 (br), 618.
2h: N-methyl-tris-fulleropyrrolidine trans-2, trans-4, cis-
2; C69H21N3 (MW 891.956); relative yield 5.8% (3.4 mg, 0.004
1
mmol); ES-MS m/z 893 (MH+); H NMR (400 MHz) δ 4.37 (d,
J ) 9.2 Hz, 1H), 4.29 (d, J ) 9.5 Hz, 1H), 4.08 (d, J ) 9.2 Hz,
1H), 3.95 (m, 4H), 3.82 (m, 4H), 3.66 (d, J ) 9.2 Hz, 1H), 2.91
(s, 3H), 2.82 (s, 3H), 2.72 (s, 3H); the low amount of obtained
compound did not allow recording of the 13C NMR spectrum;
UV-vis (CH2Cl2) λmax 225, 241, 265, 306, 460, 642, 709.
2i: N-methyl-tris-fulleropyrrolidine trans-2, equatorial, cis-
2; C69H21N3 (MW 891.956); relative yield 11.0% (6.4 mg, 0.007
1
mmol); ES-MS m/z 893 (MH+); H NMR (400 MHz) δ 4.16 (d,
J ) 6.8 Hz, 2H), 4.98 (d, J ) 9.2 Hz, 1H), 3.94 (d, J ) 9.2 Hz,
1H), 3.84 (m, 2H), 3.66 (m, 4H), 3.57 (d, J ) 11.4 Hz, 1H),
3.39 (d, J ) 11.44 Hz, 1H), 2.80 (s, 6H), 2.65 (s, 3H); the low
amount of obtained compound did not allow recording of the
13C NMR spectrum; UV-vis (CH2Cl2) λmax 225, 241, 265, 306,
440.
Acknowledgment. This work was carried out with
partial support from the EU (RTN network WONDER-
FULL), MIUR (cofin prot. 2004035502), and the Uni-
versity of Trieste. We are grateful to Dr. Fabio Hollan
(CSPA, University of Trieste) for his continuous support
with mass spectrometry.
2e: N-methyl-tris-fulleropyrrolidine trans-2, trans-4, equa-
torial; C69H21N3 (MW 891.956); relative yield 7.2% (4.2 mg,
0.005 mmol); ES-MS m/z 893 (MH+); 1H NMR (400 MHz) δ
4.38 (d, J ) 11.1 Hz, 2H), 4.17 (d, J ) 11.1 Hz, 2H), 4.12 (m,
2H), 4.03 (m, 2H), 3.94 (m, 4H), 2.89 (s, 3H), 2.88 (s, 3H), 2.76
(s, 3H); the low amount of obtained compound did not allow
recording of the 13C NMR spectrum; UV-vis (CH2Cl2) λmax 225,
241, 265, 306, 455, 540 (br), 655, 709.
JO050417T
J. Org. Chem, Vol. 70, No. 12, 2005 4713