Preparation and Characterization of Six Bis(N-methylpyrrolidine)-C60 Isomers: Magnetic Deshielding in Isomeric Bisadducts of C60

Article abstract of DOI:10.1021/jo960466t

A series isomers of bis(N-methylpyrrolidine)-C60 2 (prato bisdducts) was prepared by the 1,3-dipolar cycloaddition of N-methylazomethine ylide to C60.Six isomers were separated and characterized by ESI-MS, UV/vis, and 1H and 13C NMR spectroscopy.TThe structures of these bisadducts were assigned based on (1) comparison of their molecular symmetries with their 1H and 13C NMR spectra, (2) comparison of their UV/vis spectra with those of corresponding Bingel-Hirsch bisadducts, and (3) the order of deshielding of the methylene and N-methyl 1H NMR resonances.Prato bisaddition is less chemoselective than Bingel-Hirsch bisaddition to C60.

Full text of DOI:10.1021/jo960466t

4764
J . Org. Chem. 1996, 61, 4764-4768
P r ep a r a tion a n d Ch a r a cter iza tion of Six
Bis(N-m eth ylp yr r olid in e)-C60 Isom er s: Ma gn etic
Desh ield in g in Isom er ic Bisa d d u cts of C60
Qing Lu, David I. Schuster,* and Stephen R. Wilson*
Department of Chemistry, New York University, Washington Square, New York, New York 10003
Received March 7, 1996X
A series of isomers of bis(N-methylpyrrolidine)-C60 2 (Prato bisadducts) was prepared by the 1,3-
dipolar cycloaddition of N-methylazomethine ylide to C60. Six isomers were separated and
characterized by ESI-MS, UV/vis, and 1H and 13C NMR spectroscopy. The structures of these
bisadducts were assigned based on (1) comparison of their molecular symmetries with their 1H
and 13C NMR spectra, (2) comparison of their UV/vis spectra with those of corresponding Bingel-
Hirsch bisadducts, and (3) the order of deshielding of the methylene and N-methyl 1H NMR
resonances. Prato bisaddition is less chemoselective than Bingel-Hirsch bisaddition to C60.
In d r od u ction
The soccer ball-shaped molecule C60 appears to undergo
reactions associated with poorly-conjugated electron-
deficient alkenes.1 However, a unique feature of C60 is
that a large number of products may arise from polyad-
dition of even one reagent to C60 since it has 30 reactive
[6,6] double bonds. Well-designed polyadducts of C60 with
defined three-dimensional structures have potential for
biological applications, such as molecular recognition.2
For example, it has been reported that a water-soluble
C60 derivative inhibits HIV protease and reverse tran-
scriptase.3,4 In order to be able to design three-dimen-
sional structures based on C60, it is important to control
the chemoselectivity of the C60 polyaddition. The chem-
istry of C60 has been dominated, thus far, mainly with
investigation of its monoaddition reactions. The synthe-
sis of isomerically pure polyadducts of C60 has been
reported in only a few cases.5 For example, Hirsch et
al.5d isolated and characterized seven isomers of bis-
(ethoxycarbonyl)methylene-C60. In nucleophilic cyclo-
propanations of C60 (Scheme 1), attack at specific [6,6]
double bonds is significantly preferred. The most favor-
able positions are at the equatorial and trans-3 positions
relative to the addend already bound to the fullerene core
(Figure 1).
F igu r e 1. Positional relationships and Hirsch nomenclature
of the eight different double bonds in a C60 bisadduct relative
to the 6-6 bond carrying the first addend R.
Sch em e 1
The 1,3-dipolar cycloaddition of azomethine ylides to
C60 affording fulleropyrrolidines was reported by Prato
and co-workers.6 This high yield reaction occurs exclu-
sively across [6,6] bonds. Since the addend is sym-
metrical in N-methylpyrrolidine-C60,6a there are again
eight possibilities for bisaddition. We selected this
reaction as another candidate for the investigation of the
chemoselectivity of bisaddition to C60. In this paper, we
report the preparation, isolation, and characterization of
six isomers of bis(N-methylpyrrolidine)-C60. One would
expect different proportions of isomeric bisadducts com-
pared with that in Hirsch’s reaction, since the two
reactions proceed by totally different mechanisms.
X Abstract published in Advance ACS Abstracts, May 15, 1996.
(1) For reviews, see: (a) Hirsch, A. Angew. Chem., Int. Ed. Engl.
1993, 32, 1138. (b) Taylor, R.; Walton, D. R. M. Nature 1993, 363, 685.
(c) Diederich, F.; Isaacs, L.; Philip, D. Chem. Soc. Rev. 1994, 243. (d)
Hirsch, A. The Chemistry of the Fullerenes; Thieme Medical Publish-
ers: New York, 1994.
(2) J ensen, A. W.; Wilson, S. R.; Schuster, D. I. Bioorg. Med. Chem.,
in press.
(3) Friedman, S. H.; DeCamp, D. L.; Sijbesma, R. P.; Srdanov, G.;
Wudl, F.; Kenyon, G. L. J . Am. Chem. Soc. 1993, 115, 6506.
(4) Sijbesma, R. P.; Srdanov, G.; Wudl, F.; Castoro, J . A.; Wilkins,
C.; Friedman, S. H.; DeCamp, D. L.; Kenyon, G. L. J . Am. Chem. Soc.
1993, 115, 6510.
(5) (a) Fagan, P. J .; Calabrese, J . C.; Malone, B. J . J . Am. Chem.
Soc. 1991, 113, 9408. (b) Hawkins, J .; Meyer, A.; Lewis, T.; Bunz, U.;
Nunlist, R.; Ball, G.; Ebbesen, T.; Katsumi, T., J . Am. Chem. Soc. 1992,
114, 7954. (c) Hawkins, J .; Meyer, A.; Nambu, M. J . J . Am. Chem.
Soc. 1993, 115, 9844. (d) Hirsch, A.; Lamparth, I.; Karfunkel, H. R.
Angew. Chem., Int. Ed. Engl. 1994, 33, 437. (e) Henderson, C. C.;
Assink, R. A.; Cahill, P. A. Angew. Chem., Int. Ed. Engl. 1994, 33,
786. (f) Hirsch, A.; Lamparth, I.; Cro¨sser, T.; Karfunkel, H. R. J . Am.
Chem. Soc. 1994, 116, 9385. (g) Lamparth, I.; Maichle-Mo¨ssmer, C.;
Hirsch, A. Angew. Chem., Int. Ed. Engl. 1995, 34, 1607. (h) Wilson, S.
R.; Lu, Q. Tetrahedron Lett. 1995, 36, 5707.
(6) (a) Maggini, M.; Scorrano, G.; Prato, M. J . Am. Chem. Soc. 1993,
115, 9798. (b) Maggini, M.; Scorrano, G.; Bianco, A.; Toniolo, C.;
Sijbesma, R. P.; Wudl, F.; Prato, M. J . Chem. Soc., Chem. Commun.
1994, 305. (c) Maggini, M.; Karlsson, A.; Pasimeni, L.; Scorrano, G.;
Prato, M.; Valli, L. Tetrahedron Lett. 1994, 35, 2985. (d) Prato, M.;
Maggini, M.; Scorrano, G.; Brusatin, G.; Innocenzi, P.; Guglielmi, M.;
Meneghetti, M.; Bozio, R. Mater. Res. Soc. Symp. Proc. 1995, 359
(Science and Technology of Fullerene Materials), 351-6. (e) Prato, M.;
Maggini, M.; Scorrano, G. Proc.-Electrochem. Soc. 1994, 94 (24)
(Recent Advances in the Chemistry and Physics of Fullerenes and
Related Materials), 713-22. (f) Corvaja, C.; Maggini, M.; Prato, M.;
Scorrano, G.; Venzin, M. J . Am. Chem. Soc. 1995, 117, 8857.
S0022-3263(96)00466-5 CCC: $12.00 © 1996 American Chemical Society

Magnetic Deshielding in Bisadducts of C60
J . Org. Chem., Vol. 61, No. 14, 1996 4765
as trans-1, trans-2, trans-3, and cis-3, respectively. The
1H NMR spectra of these bisadducts match the assigned
structures. Two singlets at δ 4.67 (CH2) and δ 3.14 (CH3)
are observed in the spectrum of 2a , consistent with the
D2h symmetry of trans-1. Four doublets at δ 4.64 (J )
9.3 Hz), δ 4.46 (J ) 9.3 Hz), δ 4.32 (J ) 6.6 Hz), and δ
4.30 (J ) 6.6 Hz) along with one singlet at δ 3.05 (CH3)
are observed in the spectrum of 2b; four doublets at δ
4.41 (J ) 9.6 Hz), δ 4.32 (J ) 9.6 Hz), δ 4.16 (J ) 9.4
Hz), and δ 4.06 (J ) 9.4 Hz) along with one singlet at δ
2.92 (CH3) are observed in the spectrum of 2d ; and four
doublets at δ 4.05 (J ) 8.6 Hz), δ 4.03 (J ) 8.6 Hz), δ
3.98 (J ) 8.6 Hz), and δ 3.88 (J ) 8.6 Hz) along with one
singlet at δ 2.80 (CH3) are observed in the spectrum of
2f. These spectra are consistent with the C2 symmetries
of trans-2, trans-3, and cis-3. Each of these structures
has two nonequivalent methylene groups possessing
coupled diastereotopic protons, resulting in pairs of AB
quartets.
Bisadduct 2e was initially assigned as the e isomer
according to its order of elution (its UV/vis spectrum in
the 400-700 nm region does not match any of the UV/
vis spectra of the Hirsch bisadducts), but its 1H NMR
spectrum rules out this assignment. Four doublets are
observed at δ 4.30 (J ) 10 Hz), δ 4.16 (J ) 10 Hz), δ 4.06
(J ) 9.6 Hz), and δ 4.03 (J ) 9.6 Hz) along with one
singlet at δ 2.88 (CH3), consistent with either Cs or C2
symmetry. The e bisadduct should have two equivalent
methylene groups possessing nonequivalent protons
coupled to each other, as well as two nonequivalent
methylene groups with magnetically equivalent protons.
F igu r e 2. HPLC chromatogram of the mixture of isomeric
bisadducts of bis(N-methylpyrrolidine)-C60 2a -f. Condi-
tions: 250 × 4.6 mm “Adsorbosphere Silica” column, 1000:1:1
toluene/EtOAc/Et3N as mobile phase (1 mL/min), 4 µL injec-
tion, UV/vis detection at 340 nm.
Sch em e 2
1
Therefore, the H NMR spectrum of the e isomer should
consist of two doublets and three singlets (for two CH2
and one CH3 group).
The 13C NMR spectrum of 2e shows 35 signals (30 sp2
fullerene carbons between δ 155 and δ 128, 2 sp3 fullerene
carbons at δ 69.81 and δ 69.58, two CH2 groups at δ 70.05
and δ 69.39 and one CH3 group at δ 41.38), compatible
with the Cs symmetry of trans-4. Thus, on the basis of
1H and 13C NMR spectra, bisadduct 2e was assigned as
the trans-4 isomer (the only other possibility is cis-2,
which is much less likely to be formed due to steric
hindrance between the adjacent substituents).
Resu lts a n d Discu ssion
Bisadduct 2c, a minor product, is tentatively assigned
as the e isomer based on its UV/vis spectrum in the 400-
700 nm region. A similarity in UV/vis absorption in this
region exists between 2c and e-C62(CO2H)4,8 although no
such similarity exists between 2c and e-C62(CO2Et)4
The monoadduct, N-methylpyrrolidine-C60 (1), was
prepared and isolated according to the reported proce-
dure6a and was then subjected to the same reaction
conditions (Scheme 2) to give bis(N-methylpyrrolidine)-
C
60 isomers 2 (Prato bisadducts). Flash chromatographic
1
(Figure 3). The H NMR spectrum of 2c shows only one
separation on silica gel gave (in order of elution following
1) a fraction containing four bisadducts 2a -d and a
mixed fraction containing two additional bisadducts 2e,f
as well as trisadducts. Further separation on a semi-
preparative “Econosil Silica” HPLC column led to isola-
tion of six bisadducts 2a -f in a 7.3:20:5.6:24:18:25 ratio.
Electrospray ionization MS (ESI-MS) confirmed that all
six components are N-methylpyrrolidine-C60 bisadducts.
Analysis of the original reaction mixture on an “Adsor-
bosphere Silica” HPLC column gave virtually the same
isomer ratio as above (Figure 2). The fact that the ratio
of bisadducts is not significantly time-dependent indi-
cates similar reactivity of these bisadducts toward further
reaction.
On the basis of comparison of the UV/vis spectra
(Figure 3) of these bisadducts in the 400-700 nm region
and their order of chromatographic elution with those of
the isomers of bis(ethoxycarbonyl)methylene-C60 (Hirsch
bisadducts),7 some tentative structure assignments could
be made. On this basis, 2a , 2b, 2d and 2f were assigned
singlet at δ 4.03 for CH2 and another singlet at δ 2.83
for CH3. Apparently, the NMR spectrometer (even at 500
MHz) cannot sense the slight difference between the
three magnetically nonequivalent methylene groups. This
observation is not very surprising as a similar situation
was noted in the Hirsch isomers. Only two multiplets
at ca. δ 4.45 (CH2) and δ 1.45 (CH3) are observed in the
1H NMR spectrum of e-C62(CO2Et)4.7 Attentive analysis
of all 1H NMR spectra of the Hirsch and Prato bisadducts
indicates that when two addends on C60 approach the
(7) We repeated the Hirsch bisaddition reaction, separated the
regioisomeric bisadducts, and obtained 1H NMR spectra for trans-
2,trans-3,trans-4 equatorial and cis-3 isomers and UV/vis spectra for
trans-1,trans-2,trans-3,trans-4 equatorial, cis-3, and cis-2 isomers,
consistent with those reported in: Hirsch, A.; Lamparth, I.; Karfunkel,
H. R. Proc.-Electrochem. Soc. 1994, 94 (24) (Recent Advances in the
Chemistry and Physics of Fullerenes and Related Materials), 734-
46.
(8) For the UV/vis spectrum of e-C62(CO2H)4 in the 400-600 nm
region, see: Lamparth, I.; Hirsch, A. J . Chem. Soc., Chem. Commun.
1994, 1727.

4766 J . Org. Chem., Vol. 61, No. 14, 1996
Lu et al.
F igu r e 3. UV/vis spectra of regioisomeric bisadducts C62(CO2Et)4 (Scheme 1) and UV/vis spectra of regioisomeric bisadducts
bis(N-methylpyrrolidine)-C60 2a -f.
equatorial from the trans-1 orientation, chemical shift
differences become smaller. Indeed, this phenomenon
may be helpful in structure determination of C60 bisad-
ducts.
The methylene and N-methyl resonances in 2a -f are
all downfield with respect to typical aliphatic pyrrolidines
(for example, δ 2.32 for the N-methyl and δ 2.45 for the
R-methylene groups in N-methylpyrrolidine) because of
ring currents on the surface of the C60 cage.9 It is
interesting furthermore to compare the chemical shifts
of the methylene and N-methyl resonances in the Prato
bisadducts 2 (Table 1). The order of the chemical shifts
of the methylene and N-methyl resonances from trans-1
(9) (a) Pasquarello, A.; Schlueter, M.; Haddon, R. C. Science 1992,
257, 5077. (b) Haddon, R. C.; Cockayne, E.; Elser, V. Synth. Met. 1993,
59, 369.

Magnetic Deshielding in Bisadducts of C60
J . Org. Chem., Vol. 61, No. 14, 1996 4767
F igu r e 4. Structures of three N-methylpyrrolidine monoad-
ducts of C70
.
Ta ble 1. Or d er of th e Ch em ica l Sh ifts of th e Meth ylen e
a n d N-Meth yl 1H NMR Reson a n ces fr om tr a n s-1 to cis-3
in P r a to Bisa d d u cts 2
δ NCH3, deshielding
δ CH2, ppm
compd isomer
ppm
order
2a
2b
2d
2e
2c
2f
trans-1
4.67
3.14
3.05
2.92
2.88
2.83
2.80
1
2
3
4
5
6
trans-2 4.64 4.46 4.32 4.30
trans-3 4.41 4.32 4.16 4.06
trans-4 4.30 4.16 4.06 4.03
e
4.03
cis-3
4.05 4.03 3.98 3.88
F igu r e 5. Chemoselectivities of Hirsch (Scheme 1) and Prato
bisadditions (Scheme 2).
Ta ble 2. Or d er of th e Ch em ica l Sh ifts of th e Meth ylen e
a n d Meth yl 1NMR Reson a n ces fr om tr a n s-2 to cis-3 in
Hir sch Bisa d d u cts C62(CO2Et)4 (Sch em e 1)
Su m m a r y
Prato bisadducts 2 were prepared by the 1,3-dipolar
cycloaddition of N-methylazomethine ylide to C60. Six
isomers were separated and characterized by ESI-MS,
deshielding
δ CH2, ppm
δ CH3, ppm
isomer
order
trans-2
trans-3
trans-4
e
4.69
4.56
4.53
4.52
4.46
4.46
1.61
1.52
1.50
1.48
1.44
1.43
1
2
3
4
5
1
UV/vis, and H and 13C NMR spectroscopy. The struc-
tures of these bisadducts were assigned on the basis of
(1) comparison of their different molecular symmetries
with their 1H and 13C NMR spectra, (2) comparison of
their UV/vis spectra with those of the bisadducts from
the Bingel-Hirsch cyclopropanation, and (3) the order
4.49 4.46 4.43
4.48 4.42
1.48 1.46 1.42
1.46 1.40
cis-3
to cis-3 can be attributed to differing ring currents
associated with the overall π-bonding structure of iso-
meric C60 derivatives. The same deshielding order of the
methylene and methyl resonances is observed in the
Hirsch bisadducts (Table 2).7 The structure assignments
made above for trans-1, trans-2, trans-3, trans-4, e and
cis-3 Prato bisadducts are strongly supported by this
observation.
The chemical shifts of the methyl groups in the
N-methylpyrrolidine monoadducts of C70 (Figure 4), at δ
2.74, δ 2.60 and δ 2.51 for 3a (1,9-isomer), 3b (7,8-
isomer), and 3c (22,23-isomer), respectively, indicate the
influence of the curvature of the fullerene surface on the
deshielding effect.10 Deshielding of the methyl substitu-
ent is more pronounced at the region of sharper surface
curvature. Deshielding in the polar region of C70 has
been observed in isomeric C70 isoxazolines.11 We suggest
that the shape of the C60 sphere may be somewhat
distorted after Prato bisaddition. Positioning of substit-
uents on the regions of the C60 surface corresponding to
variations in surface curvature, proceeding from trans-1
(most spherical) to cis-3 (most flat), could account for the
deshielding order shown in Table 1. This relative order
of chemical shifts may prove highly useful in structure
assignments of other series of C60 bisadducts when the
1
of deshielding of the methylene and N-methyl H NMR
resonances. Prato bisaddition is less chemoselective than
Hirsch bisaddition to C60.
Exp er im en ta l Section
Gen er a l In for m a tion . Commercial reagents were used as
received. C60 (>99%) was obtained from MER Corp.
P r ep a r a tion of Mon o(N-m eth ylp yr r olid in e)-C60 (1). A
mixture of C60 (110 mg, 0.15 mmol), N-methylglycine (27 mg,
0.30 mmol), and paraformaldehyde (23 mg, 0.75 mmol) was
heated at reflux in 200 mL of toluene under Ar for 2 h. The
resulting brown solution was washed with water, dried over
Na2SO4, and concentrated in vacuo. The crude product was
purified by flash chromatography on silica gel (eluent: toluene
and then toluene/triethylamine 100:1), affording 52 mg (45%)
of the monoadduct: ESI-MS (TFA/toluene/MeOH) m/z 778 (M
+ H+); 1H NMR (200 MHz, CDCl3/CS2) δ 4.42 (s, 4H), 3.02 (s,
3H).
P r ep a r a tion of Bis(N-m eth ylp yr r olid in e)-C60 (2a -f).
N-Methylpyrrolidine bisadducts of C60 were synthesized from
the monoadduct using the same experimental conditions as
those described above. Flash chromatography on silica gel
(eluent: 100:1 toluene/triethylamine then 100:5:1 toluene/
EtOAc/triethylamine) was used for preliminary product sepa-
ration. The first fraction contains bisadducts 2a -d . The
second fraction includes two further bisadducts, 2e and 2f, as
well as trisadducts. A semipreparative 250 × 10 mm “Econosil
Silica” HPLC column was used to isolate a total of six
bisadducts, 2a , 2b, 2c, 2d , 2e, and 2f, in a 7.3:20:5.6:24:18:25
ratio [eluent: 1000:1:1 toluene/AcOEt/triethylamine for 2a , 2b,
2c and 2d ; 1000:1:1 toluene/MeOH/triethylamine for 2e and
2f (3 mL/min); UV/vis detection at 340 nm].
1
addends have groups which give distinct H NMR signals.
It is worthy of note that Hirsch bisaddition (Scheme
1) is more chemoselective than Prato bisaddition (Scheme
2). Thus, e-C62(CO2Et)4 and trans-3-C62(CO2Et)4 are
preferentially favored in Hirsch bisaddition, while trans-
2, trans-3, trans-4, and cis-3 are the major isomers in
Prato bisaddition (Figure 5).
2a : ESI-MS (TFA/toluene/MeOH) m/z 835 [M + H+]; 1H
NMR (200 MHz, CDCl3/CS2) δ 4.67 (s, 4H), 3.14 (s, 6H); UV/
vis (400-700 nm, CH2Cl2) see Figure 3.
(10) Wilson, S. R.; Lu, Q. J . Org. Chem. 1995, 60, 6496.
(11) Meier, M. S.; Poplawska, M.; Compton, A. L.; Shaw, J . P.;
Selegue, J . P.; Guarr, T. F. J . Am. Chem. Soc. 1994, 116, 7044.
2b: ESI-MS (TFA/toluene/MeOH) m/z 835 [M + H+]; 1H
NMR (200 MHz, CDCl3/CS2) δ 4.64 (d, J ) 9.3 Hz, 2H), 4.46

4768 J . Org. Chem., Vol. 61, No. 14, 1996
Lu et al.
(d, J ) 9.3 Hz, 2H), 4.32 (d, J ) 6.6 Hz, 2H), 4.30 (d, J ) 6.6
Hz, 2H), 3.05 (s, 6H); UV/vis (400-700 nm, CH2Cl2) see Figure
3.
(2C-sp3), 69.58 (2C-sp3), 69.39 (CH2), 41.38 (CH3); UV/vis (400-
700 nm, CH2Cl2) see Figure 3.
2f: ESI-MS (TFA/toluene/MeOH) m/z 835 [M + H+]; 1H
NMR (200 MHz, CDCl3/CS2) δ 4.05 (d, J ) 8.6 Hz, 2H), 4.03
(d, J ) 8.6 Hz, 2H), 3.98 (d, J ) 8.6 Hz, 2H), 3.88 (d, J ) 8.6
Hz, 2H), 2.80 (s, 6H); UV/vis (400-700 nm, CH2Cl2) see Figure
3.
2c: ESI-MS (TFA/toluene/MeOH) m/z 835 [M + H+]; 1H
NMR (200 MHz, CDCl3/CS2) δ 4.03 (s, 4H), 2.83 (s, 6H); UV/
vis (400-700 nm, CH2Cl2) see Figure 3.
2d : ESI-MS (TFA/toluene/MeOH) m/z 835 [M + H+]; 1H
NMR (200 MHz, CDCl3/CS2) δ 4.41 (d, J ) 9.6 Hz, 2H), 4.32
(d, J ) 9.6 Hz, 2H), 4.16 (d, J ) 9.4 Hz, 2H), 4.06 (d, J ) 9.4
Hz, 2H), 2.92 (s, 6H); UV/vis (400-700 nm, CH2Cl2) see Figure
3.
Ack n ow led gm en t. We thank NSF (CHE-9400666)
and the NYU Research Challenge Fund for partial
financial support of this work. We also thank MER
Corp. for a gift of C60.
2e: ESI-MS (TFA/toluene/MeOH) m/z 835 [M + H+]; 1H
NMR (200 MHz, CDCl3/CS2) δ 4.30 (d, J ) 10.0 Hz, 2H), 4.16
(d, J ) 10.0 Hz, 2H), 4.06 (d, J ) 9.6 Hz, 2H), 4.03 (d, J ) 9.6
Hz, 2H), 2.88 (s, 6H); 13C NMR (500 MHz, CDCl3/CS2) δ 154.38
(2C), 152.45 (2C), 151.24 (2C), 150.75 (2C), 150.48 (2C), 149.51
(1C), 149.08 (2C), 148.19 (2C), 147.77 (2C), 147.27 (2C), 146.12
(2C), 145.98 (4C), 145.47 (2C), 145.83 (2C), 145.81 (2C), 144.51
(2C), 142.53 (2C), 142.03 (2C), 141.67 (2C), 141.65 (2C), 141.30
(2C), 141.16 (2C), 139.07 (2C), 138.53 (2C), 136.01 (2C), 135.33
(2C), 131.16 (1C), 128.91 (1C), 128.15 (1C), 70.05 (CH2), 69.81
Su p p or tin g In for m a tion Ava ila ble: 1H, 13C NMR and
ESI-MS spectra (18 pages). This material is contained in
libraries on microfiche, immediately follows this article in the
microfilm version of the journal, and can be ordered from the
ACS; see any current masthead page for ordering information.
J O960466T