A rigid macrocyclic bis-malonate for the regioselective preparation of trans-1 and trans-3 fullerene bis-adducts

Article abstract of DOI:10.1016/j.tetlet.2013.04.024

A macrocyclic bis-malonate incorporating two rigid di(phenylethynyl)silane moieties has been prepared and used to functionalize C₆₀ in a double Bingel cyclopropanation. Two regioisomeric bis-adducts have been thus obtained, namely the trans-1 and trans-3 isomers. The formation of these specific isomers is favored by both the size of the starting macrocycle and the minimum of strain in the final products.

Full text of DOI:10.1016/j.tetlet.2013.04.024

Tetrahedron Letters 54 (2013) 3160–3163
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Tetrahedron Letters
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A rigid macrocyclic bis-malonate for the regioselective preparation
of trans-1 and trans-3 fullerene bis-adducts
⇑
David Sigwalt, Michel Holler, Jean-François Nierengarten
Laboratoire de Chimie des Matériaux Moléculaires, Université de Strasbourg et CNRS (UMR 7509), Ecole Européenne de Chimie, Polymères et Matériaux (ECPM), 25 rue
Becquerel, 67087 Strasbourg Cedex 2, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A macrocyclic bis-malonate incorporating two rigid di(phenylethynyl)silane moieties has been prepared
and used to functionalize C60 in a double Bingel cyclopropanation. Two regioisomeric bis-adducts have
been thus obtained, namely the trans-1 and trans-3 isomers. The formation of these specific isomers is
favored by both the size of the starting macrocycle and the minimum of strain in the final products.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 6 March 2013
Accepted 5 April 2013
Available online 13 April 2013
Keywords:
Fullerene
Malonate
Macrocycle
Regioselectivity
The polyfunctionalization of C60 through multiple addition reac-
tions has generated unprecedented stereochemical problems.1 In
the case of fullerene bis-adducts, mixtures of regioisomers are ob-
tained by successive reactions at the C60 core. Actually, mono-func-
tionalized C60 derivatives possess nine different 6–6 bonds (bonds
at the junction between two six-membered rings) that can react in
a second addition (Fig. 1).2,3 As a typical example, the sequential
double Bingel cyclopropanation4 of C60 with 2-bromomalonate in
the presence of a base gave seven out of the eight possible
the specific addition pattern of the product depends on the length
of the spacers. In this Letter, we now show that this concept is not
limited to flexible cyclobis-malonates. The reaction of C60 with a ri-
gid macrocyclic bis-malonate is also well suited for the regioselec-
tive preparation of specific fullerene bis-adducts.
The preparation of the rigid macrocyclic bis-malonate is de-
picted in Scheme 1. Treatment of alkyne 19 with nBuLi (1 equiv)
in THF at 0 °C followed by reaction with di-tert-butylsilyl bis(tri-
fluoromethanesulfonate) (tBu2Si(OTf)2, 0.5 equiv) gave 2 in 81%
yield. Cleavage of the tetrahydropyran-2-yl (THP) protecting
groups was then achieved by treatment of 2 with p-toluenesulfonic
acid (pTsOH) in ethanol. Reaction of the resulting diol (3) with mal-
onyl chloride in the presence of 4-dimethylaminopyridine (DMAP)
under pseudo high dilution conditions afforded 4 in 9% yield.10
Macrocycle 4, which has a ring size of 40 atoms, was characterized
by NMR spectroscopy and mass spectrometry. Crystals suitable for
X-ray crystal analysis were also obtained by slow diffusion of n-
pentane into a CH2Cl2 solution of 4.11 As shown in Figure 2, the
X-ray crystal structural analysis of 4 reveals a centro-symmetrical
structure for the macrocyclic bis-malonate with Si(1)–Si(10) and
C(11)–C(110) distances of 10.424(1) and 17.688(2) Å, respectively.
The reaction of 4 with C60 was initially performed under the
typical conditions developed by Diederich and co-workers for the
preparation of fullerene bis-adducts from bis-malonates.6a Specifi-
cally, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was added to a
solution of 4, C60, and iodine in toluene at room temperature.
Whereas reagent 4 was rapidly consumed, all the starting C60
was recovered at the end of the reaction thus showing that a fast
decomposition of 4 occurred under these conditions. In order to
prevent decomposition of this reagent, the reaction was then
C
60(C(CO2Et)2)2 bis-adducts,2 only the cis-1 isomer was not formed
for steric reasons. The first efficient methodology allowing the reg-
ioselective preparation of C60 bis-adducts has been introduced by
Diederich and co-workers.5 Starting from a mono-functionalized
fullerene derivative in which the addend is carrying a reactive
group at the end of a tether, they have shown that an intramolec-
ular reaction provides a specific bis-adduct. The regioselectivity of
the cyclization reaction results from the length of the spacer and
steric constraints allowing the reactive group to attack a specific
double bond on the fullerene scaffold. In a simplified version, C60
has been directly treated with a bis-functional reagent in which
the two reactive groups are interconnected by a spacer.6,7 Macro-
cyclization reactions onto the C60 core provide directly bis-adducts
with good regioselectivities. This is for example the case for the
reaction of C60 with bis-malonates when quite rigid spacers are
used.6 An alternative concept using flexible cyclo-oligomalonates
has been also reported.8 The regioselectivity of these reactions is
governed by the distribution of strain within the macrocycle and
⇑
Corresponding author. Tel.: +33 368 852 763; fax: +33 368 852 774.
E-mail address: nierengarten@unistra.fr (J.-F. Nierengarten).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.04.024

D. Sigwalt et al. / Tetrahedron Letters 54 (2013) 3160–3163
3161
Figure 1. Addition of a second addend to a C2v-symmetrical C60 mono-adduct can in principle lead to nine different regioisomeric bis-adducts. Relative to the first addend, the
second one can be located either in the same hemisphere (cis), in the opposite hemisphere (trans), or on the equatorial belt (e). For identical addends, a second attack onto the
e-edge or e-face positions leads to identical products. In the particular case of C60(C(CO2Et)2)2, the symmetry of the bis-adducts can be either C2 (cis-3, trans-2, trans-3), Cs (cis-
1, cis-2, e, trans-4), or D2h (trans-1).
OR
OTHP
(i)
2 R = THP
3 R = H
Si
(ii)
H
1
OR
O
O
O
O
O
(iii)
Si
Si
O
O
O
4
(iv)
O
O
O
O
O
O
O
O
Si
O
O
Si
Si
+
O
O
O
Si
O
O
O
5
6
trans-1 (D2h
)
trans-3 (C2)
Scheme 1. Reagents and conditions: (i) nBuLi, THF, 0 °C, 1 h, then tBu2Si(OTf)2, 0 °C, 1 h (81%); (ii) pTsOH, EtOH, rt, 12 h (78%); malonyl chloride, DMAP, CH2Cl2, rt, 12 h (9%);
(iv) C60, DBU, I2, PhMe, ꢀ15 °C, 1 h (5: 8%, 6: 18%).
performed at lower temperatures. No reaction was observed at
temperature lower than ca. ꢀ20 °C and the best results were ob-
tained when the reaction mixture was stirred for 1 h at ꢀ15 °C. Un-
der optimized conditions,12 the reaction of 4 with C60 gave the
regioisomeric bis-adducts 5 and 6 in 8% and 18% isolated yields,
respectively. Fullerene derivatives 5 and 6 were characterized by
1H and 13C NMR, UV–vis, and IR spectroscopies. In addition, their
structure was confirmed by MALDI-TOF mass spectrometry show-
ing the expected molecular ion peak in both cases.12
In the case of 5, the relative position of the two cyclopropane
rings on the fullerene surface was unambiguously established by
the D2h symmetry deduced from the 1H and 13C NMR spectra.

3162
D. Sigwalt et al. / Tetrahedron Letters 54 (2013) 3160–3163
Figure 2. ORTEP plot of the structure of 4 (the thermal ellipsoids are shown at 50%
probability level; C: gray; O: red, Si: yellow; H: white).
Among all the possible regioisomeric fullerene bis-adducts, a sym-
metry as high as D2h can only be present if the addition pattern on
the fullerene moiety is trans-1.13 Additionally, the greenish color
and the absorption spectrum of 5 are also diagnostic signatures
of a trans-1 addition pattern (Fig. 3).
The trans-1 addition pattern was nicely confirmed by the X-ray
crystal structure analysis of 5.14 As shown in Figure 4, compound 5
adopts a [1]rotaxane structure with the trans-1 C60 bis-adduct core
located within the cavity of the surrounding macrocyclic bis-mal-
onate. As observed for 4, the structure of 5 is also centro-symmet-
ric. However, due to the connection to the fullerene core, the Si(1)–
Si(10) (16.280(2) Å) and C(31)–C(310) (9.923(6) Å) distances are sig-
nificantly different for 5 when compared to 4. Indeed, the two rigid
bis(phenylethynyl)silane moieties are connected by two flexible
malonate subunits providing sufficient adaptability to the system
to form the trans-1 C60 bis-adduct during the double Bingel
cyclopropanation.
Figure 4. ORTEP plots of the structure of 5 (the thermal ellipsoids are shown at 50%
probability level; C: gray; O: red, Si: yellow; H: white; the co-crystallized CHCl3
molecules are not shown for clarity).
semi-empirical level. The trans-2 isomer was effectively found
noticeably higher in energy than 5 (
D
E = ꢀ22 kJ/mol) and 6
(D
E = ꢀ41 kJ/mol). Importantly, the increase in energy observed
The molecular symmetry (C2) deduced from the 1H and 13C
NMR spectra of 6 suggests that this bis-adduct could be either a
trans-2 or a trans-3 regioisomer. The UV–vis spectrum of 6 is in-
deed fully consistent with a trans-3 bis-adduct (Fig. 3). The absorp-
tion spectra of C60 bis-adducts being highly dependent on the
addition pattern and characteristic for each of the regioisomers,2,6
the stereochemistry of compound 6 was thus elucidated. To further
support this structural assignment, computational studies were
also performed. The molecular geometry of the various regioisom-
ers (trans-1, trans-2, and trans-3) was optimized with SPARTAN’10
Macintosh Parallel Edition (Wavefunction Inc., USA) at the AM1
when going from the trans-3 (6) to the trans-1 isomer (5) is in good
agreement with the experimental product distribution. The differ-
ence in heat of formation for the various regioisomers reflects the
difference in strain within the rigid parts of the macrocyclic bis-
malonate. The two regioisomers in which this strain is minimal
are actually formed in the double Bingel cyclopropanation of C60
with bis-malonate 4. In contrast, the steric constraints are too
important in the case of the trans-2 regioisomer thus its formation
is prevented.
In conclusion, the reaction of a rigid macrocyclic bis-malonate
with C60 gave access to fullerene bis-adducts with an excellent reg-
ioselectivity. The formation of specific isomers is favored by both
the size of the starting macrocycle and the minimum of strain in
the final products. With its trans-1 addition pattern combined to
a peculiar [1]rotaxane structure, bis-adduct 5 is perfectly suited
for further functionalization with two additional malonate moie-
ties to produce fullerene tetra-adducts with a D2h-symmetrical
all-e addition pattern.15,16 In this way, a wide range of unprece-
dented nanomaterials constructed around a central fullerene core
will become accessible. This will be easily achieved by combining
this chemistry with our approach based on the use of click reac-
tions for the successive grafting of different functional groups onto
the fullerene scaffold.17 Work in this direction is under way in our
laboratory.
Acknowledgments
This research was supported by the CNRS, the University of
Strasbourg and the Agence Nationale de la Recherche (ANR, Pro-
gramme Blanc 2011, Sweet60s). We further thank L. Brelot and C.
Bailly for the X-ray crystal structure resolutions and M. Schmitt
for the high field NMR measurements.
Figure 3. Absorption spectra (CH2Cl2) of compounds
characteristic features of trans-1 (5) and trans-3 (6) bis-addition patterns.
5 and 6 revealing the

D. Sigwalt et al. / Tetrahedron Letters 54 (2013) 3160–3163
3163
Crystallographic data: formula: C58H64O8Si2 (M = 945.27 g molꢀ1); crystal
system: monoclinic, space group P 21/c; a = 8.0891(4) Å; b = 11.9245(6) Å;
c = 28.5114(14) Å; b = 97.852(1)°; V = 2724.4(2) Å3; Z = 2; F(000) = 1008; a total
of 23,609 reflections collected; 1.85°< h <30.00°, 7933 independent reflections
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.
04.024.
with 4572 having I >2r
(I); 313 parameters; final results: R1(F2) = 0.0524;
wR2(F2) = 0.0985, goof = 1.002 (CCDC 927709).
12. Compounds 5 and 6. DBU (0.16 mL, 1.06 mmol) was added to a stirred solution
of C60 (156 mg, 0.22 mmol), I2 (138 mg, 0.54 mmol), and
4 (205 mg,
0.22 mmol) in a mixture of toluene (312 mL) and CH2Cl2 (30 mL) at ꢀ15 °C.
The resulting solution was stirred for 1 h, then filtered through a short plug of
SiO2 (CH2Cl2) and evaporated. Column chromatography (SiO2, toluene/
References and notes
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cyclohexane 6:4) gave
5 (30 mg, 8%) and 6 (66 mg, 18%). Compound 5:
Greenish–brown solid. IR (neat): 2160 (C„C), 1732 (C@O). UV/vis (CH2Cl2):
246 (100,500), 256 (105,900), 327 (24,000), 410 (sh, 2800), 442 (1900), 471
(2500). 1H NMR (400 MHz, CDCl3): 7.47 (d, J = 8 Hz, 8H), 7.36 (d, J = 7 Hz, 8H),
5.58 (s, 8H), 1.13 (s, 36). 13C NMR (100 MHz, CDCl3): 163.7, 144.7, 144.2, 144.1,
143.3, 142.2, 140.9, 138.2, 134.9, 132.5, 131.3, 125.0, 106.0, 90.3, 69.7, 69.3,
43.6, 28.1, 27.9, 20.0. MS (MALDI-TOF): 1661 ([M]+, calcd for C118H60O8Si2:
1661.9). Compound 6: Dark brown solid. IR (neat): 2160 (C„C), 1727 (C@O).
UV/vis (CH2Cl2): 252 (155,700), 272 (sh, 97400), 320 (sh, 30,400), 380 (7900),
411 (3400), 422 (2700), 488 (2400), 580 (sh, 800), 638 (sh, 300), 688 (200). 1
H
NMR (400 MHz, CDCl3): 7.44 (d, J = 7 Hz, 4H), 7.37 (d, J = 7 Hz, 4H), 7.33 (d,
J = 7 Hz, 4H), 7.27 (d, J = 7 Hz, 4H), 5.60 (d, J = 11 Hz, 2H), 5.57 (d, J = 11 Hz, 2H),
5.34 (d, J = 11 Hz, 2H), 5.15 (d, J = 11 Hz, 2H), 1.12 (s, 18H), 1.11 (s, 18H). 13C
NMR (100 MHz, CDCl3): 163.0, 162.7, 146.6, 146.4 (two peaks), 146.2, 145.8,
145.7, 145.5, 145.2, 145.0, 144.6, 144.4, 144.3, 144.2, 144.1, 143.6, 143.2 (two
peaks), 143.1, 143.0, 142.3, 142.0, 141.7, 141.4, 141.1, 139.9, 138.3, 136.8,
134.9, 134.7, 132.4, 132.0, 130.8, 130.6, 124.7, 124.5, 106.4 (two peaks), 90.7,
90.4, 71.3, 70.9, 69.2, 69.1, 51.9, 28.0, 27.9, 19.3. MS (MALDI-TOF): 1660.4
([M]+, calcd for C118H59O8Si2: 1660.9).
13. For examples of trans-1 fullerene bis-adducts, see: (a) Bourgeois, J.-P.;
Echegoyen, L.; Fibbioli, M.; Pretsch, E.; Diederich, F. Angew. Chem., Int. Ed.
1998, 37, 2118–2121; (b) Bourgeois, J.-P.; Diederich, F.; Echegoyen, L.;
Nierengarten, J.-F. Helv. Chim. Acta 1998, 81, 1835–1844; (c) Bourgeois, J.-P.;
Woods, C. R.; Cardullo, F.; Habicher, T.; Nierengarten, J.-F.; Gehrig, R.;
Diederich, F. Helv. Chim. Acta 2001, 84, 1207–1226.
14. Crystals suitable for X-ray crystal structure analysis were obtained by slow
evaporation of a CS2/CHCl3 solution of 5. Data were collected at 173 K on a Bruker
APEX-II CCD diffractometer (MoKa radiation, k = 0.71073 Å). The structure was
solved by direct methods (SHELXS-97) and refined against F2 using the SHELXL-97
software. The nonhydrogen atoms were refined anisotropically, using weighted
full-matrix least-squares on F2. The H-atoms were included in calculated
positions and treated as riding atoms using SHELXL default parameters.
Crystallographic data: formula: (C118H60O8Si2)(CHCl3)2 (M = 1900.58 gmolꢀ1);
7. (a) Isobe, H.; Tokuyama, H.; Sawamura, M.; Nakamura, E. J. Org. Chem. 1997, 62,
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10. Compound 4. A solution of DMAP (490 mg, 4.01 mmol) in CH2Cl2 (90 mL) was
added dropwise over 12 h to a stirred solution of 3 (610 mg, 1.51 mmol) and
malonyl chloride (0.16 mL, 1.64 mmol) in CH2Cl2 (750 mL) at room
temperature. The mixture was filtered through a short plug of SiO2 (CH2Cl2)
and evaporated. Column chromatography (SiO2, cyclohexane/CH2Cl2 2:8) gave
5 (135 mg, 9%). Colorless solid. IR (neat): 2164 (CC), 1733 (C@O). 1H NMR
(400 MHz, CDCl3): 7.48 (d, J = 7 Hz, 8H), 7.21 (d, J = 7 Hz, 8H), 5.12 (s, 8H), 3.47
(s, 4H), 1.22 (s, 36). 13C NMR (100 MHz, CDCl3): 166.0, 135.8, 132.4, 128.2,
123.3, 106.4, 89.4, 66.8, 41.9, 28.0, 19.9. MS (MALDI-TOF): 945 (100%, [M]+,
crystal system: monoclinic, space group
P
21/c; a = 13.7434(10) Å;
b = 24.2628(17) Å; c = 12.8120(9) Å; b = 95.214(2)°; V = 4254.5(5) Å3; Z = 2;
F(000) = 1952; a total of 30,649 reflections collected; 1.68°< h <28.27°, 10,442
independentreflections with5488 having I >2r(I);619 parameters; finalresults:
R1(F2) = 0.0879; wR2(F2) = 0.2374, goof = 1.052 (CCDC 927710).
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Athans, A. J.; Echegoyen, L. Eur. J. Org. Chem. 2009, 3396–3403.
16. Preliminary results revealed that the reaction of compound 5 with 2 equiv of a
malonate derivative in the presence of I2 and DBU gave the corresponding D2h
-
symmetrical all-e fullerene tetra-adduct in good yields.
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calcd for
C
58H64O8Si2: 945.3), 888 (63%, [MꢀtBu]+, calcd for C54H55O8Si2:
888.2), 805 (6%, [MꢀSi(tBu)2+2H]+, calcd for C50H48O8Si1: 805.0).
11. Crystals suitable for X-ray crystal structure analysis were obtained by slow
diffusion of n-pentane into a CH2Cl2 solution of 4. Data were collected at 173 K
on a Bruker APEX-II CCD diffractometer (MoK
a radiation, k = 0.71073 Å). The
structure was solved by direct methods (SHELXS-97) and refined against F2 using
the SHELXL-97 software. The nonhydrogen atoms were refined anisotropically,
using weighted full-matrix least-squares on F2. The H-atoms were included in
calculated positions and treated as riding atoms using SHELXL default parameters.