Absolute stereochemistry of chiral, C60 fullerene bis-adducts

Article abstract of DOI:10.1080/10242430210704

To determine the absolute configuration of chiral fullerene bis-adducts, we have studied the double Bingel reaction of C₆₀ with chiral tether (2S,3S)-(-)-9 derived from (R,R)-(+ -tartaric acid, and have succeeded in isolating two possible chiral bis-adducts 10a (5%) and 10b (2%) in addition to the C_s-symmetrically added derivative 10c (40%). The CD spectra of chiral bis-adducts [CD(+)281]-10a and [CD(-)281]-10b show very intense Cotton effects, which are almost of mirror image, indicating that their chiral C₆₀ π-electron systems are enantiomeric each other. The ¹H and ¹³C NMR spectra of 10a and 10b indicate that they have C₂-symmetrical structures, and the vicinal coupling constants between two equivalent protons H-2 and H-2′ were determined as 1.2 Hz for 10a and 1.8 Hz for 10b, respectively by the ¹³C satellite band method. From the conformational analyses, the absolute configurations of these chiral C₆₀ fullerene bis-adducts were unambiguously determined as [CD(+)281]-(S,S,^fC)-10a and [CD(-)281]-(S,S,^fA) -10b, respectively.

Full text of DOI:10.1080/10242430210704

Enantiomer
ISSN: 1024-2430 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/gena20
Absolute Stereochemistry of Chiral C 60 Fullerene
Bis-Adducts
Kazuhiro Yoshida , Shuichi Osawa , Kenji Monde , Masataka Watanabe &
Nobuyuki Harada
To cite this article: Kazuhiro Yoshida , Shuichi Osawa , Kenji Monde , Masataka Watanabe
& Nobuyuki Harada (2002) Absolute Stereochemistry of Chiral C 60 Fullerene Bis-Adducts,
Enantiomer, 7:1, 23-32, DOI: 10.1080/10242430210704
To link to this article: http://dx.doi.org/10.1080/10242430210704
Published online: 17 Sep 2010.
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Date: 17 July 2016, At: 21:55

Enantiomer, Vol. 7, pp.23–32
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Copyright 2002 Taylor & Francis
1024-2430/02 $12.00 + .00
Short Communication
Absolute Stereochemistry of Chiral C60
Fullerene Bis-Adducts
Kazuhiro Yoshida,
Shuichi Osawa,
Kenji Monde,
ABSTRACT To determine the absolute configuration of chiral fullerene
bis-adducts, we have studied the double Bingel reaction of C60 with chiral
tether (2S,3S)-( )-9 derived from (R,R)-(+)-tartaric acid, and have suc-
ceeded in isolating two possible chiral bis-adducts 10a (5%) and 10b (2%)
in addition to the Cs-symmetrically added derivative 10c (40%). The CD
spectra of chiral bis-adducts [CD(+)281]-10a and [CD( )281]-10b show
very intense Cotton effects, which are almost of mirror image, indicating
that their chiral C60 -electron systems are enantiomeric each other. The
1H and 13C NMR spectra of 10a and 10b indicate that they have C2-
symmetrical structures, and the vicinal coupling constants between two
equivalent protons H-2 and H-20 were determined as 1.2 Hz for 10a and
1.8 Hz for 10b, respectively by the 13C satellite band method. From the
conformational analyses, the absolute configurations of these chiral C60
fullerene bis-adducts were unambiguously determined as [CD(+)281]-
(S,S,fC )-10a and [CD( )281]-(S,S,fA )-10b, respectively.
Masataka Watanabe,
and Nobuyuki Harada
Institute of Multidisciplinary
Research for Advanced Materials,
Tohoku University, Sendai, Japan
KEYWORDS chiral fullerene, Bingel reaction, HPLC separation, absolute stereo-
chemistry, CD Cotton effects, 1H and 13C NMR spectra, 13C satellite band method,
conformational analysis
ullerene C60 is a symmetrical and achiral molecule. However, the
addition reaction at two chiral positions of C60 skeleton makes the
F
-electron system of fullerene chiral. Synthetic and configurational
studies of such chiral fullerene bis-adducts have been carried out by sev-
eral groups. For example, Nakamura et al. first synthesized chiral bis-
adduct 1 using a chiral tether and assigned its absolute configuration
as (fC ) on the basis of MM2/Monte Carlo calculation [1] (Chart 1).
Diederich et al. also synthesized chiral bis-adduct 2 as a sole prod-
uct by the double Bingel reaction and the absolute stereochemistry of
[CD(+)280]-2 was determined as (S,S,fC), because the molecular me-
chanics calculation results indicated that among two possible diastere-
omeric bis-adducts, diastereomer (S,S,fC)-2 is much more stable than the
other diastereomer (S,S,fA)-2 [2]. The same absolute configuration was
determined by the theoretical calculation of CD spectra of chiral bis-
adducts and related compounds based on the -electron SCF-CI-DV
Received November 15, 2001;
in final form December 7, 2001.
Address correspondence to
Prof. Nobuyuki Harada, Institute of
Multidisciplinary Research for
Advanced Materials, Tohoku
University, 2-1-1 Katahira, Aoba,
Sendai 980-8577, Japan. E-mail:
n-harada@tagen.tohoku.ac.jp
23

CHART 1 Previously reported chiral C60 fullerene bis-adducts.
MO method [3]. Nishimura et al. reported other chi-
ral bis-adduct 3 using a chiral tether prepared from
2,3-butanediol [4]. They also tentatively assigned the
absolute configuration of 3 as shown in Chart 1
on the basis of molecular mechanics calculation re-
sults. Shinkai et al. reported the synthesis of boron-
containing chiral bis-adduct 4, the absolute config-
uration of which was assigned by comparison of its
CD spectrum with that of 2 [5].
In most cases only one of two possible diastere-
omers has been isolated and employed for abso-
lute configurational studies, and its stereochemistry
has been determined by the assumption that the
isolated diastereomer should be more stable than
another non-isolated diastereomer. To compare the
stability of two possible diastereomers, their rela-
tive steric energies were calculated by the empirical
molecular mechanics method. Therefore there are
two points of ambiguity in those studies of deter-
mination of absolute configuration. The first point
is that the isolated and major product is not always
the more stable compound. The second is that the
molecular mechanics is an empirical method to cal-
culate steric energy, and therefore it is not guaran-
teed that the conformer obtained by calculation is
the most stable one. In some cases, the isomer ob-
tained by calculation as the most stable conformer
may not be the true one. Therefore it is essential to
isolate two possible diastereomers and to compare
their data. To overcome the weak points of previous
24
K. YOSHIDA ET AL.

absolute configurational studies and to unambigu-
ously determine the absolute stereochemistry of chi-
ral C60 bis-adducts, we took the following strategies.
The double Bingel reaction of C60 with a relatively
tight tether containing acetonide moiety yielded only
a single diastereomer 2 [2]. However, if a loose and
more flexible chiral tether with known absolute con-
figuration is employed, two possible diastereomers
would be obtained and it is relatively easy to discrim-
diastereomers, which was separated and purified by
successive short column chromatography on silica
gel (1, toluene: 2, CHCl3/MeOH = 97/3), flash
column chromatography on silica gel (CHCl3/
toluene = 7/1), and HPLC on silica gel (CHCl3/
toluene = 1/4) yielding chiral bis-adducts 10a (5%)
and 10b (2%) in addition to the Cs-symmetrically
added derivative 10c (40%) (Chart 2). The CD spec-
tra of chiral bis-adducts [CD(+)281]-10a and [CD
( )281]-10b show very intense Cotton effects, which
are almost of mirror image, indicating that their chi-
ral C60 -electron systems are enantiomeric each
other (Figures 1 and 2). On the other hand, the ma-
jor product [CD(+)310]-10c exhibits very weak CD
Cotton effects reflecting its achiral C60 -electron
system (Figure 3).
1
inate their stereostructures by comparing H NMR
spectral data of two diastereomers. Since the chiral-
ity of a tether part can be used as an internal reference
of absolute configuration, the absolute configuration
of chiral C60 part would be determined. As a loose
and flexible tether, we have selected (2S,3S)-( )-2,3-
dimethoxybutane-1,4-diyl bis(ethyl malonate) 9,
which was prepared as shown in Scheme 1.
The double Bingel reaction of C60 with (2S,3S)-
( )-9 in the presence of I2 and 1,8-diazabicyclo[5.4.0]
undec-7-ene (DBU) in toluene gave a mixture of
Both compounds 10a and 10b have structures
1
of C2-symmetry, because their 13C and H NMR
spectra show 38 carbon peaks and 7 proton signals,
respectively [6,7]. On the other hand, since 13C and
SCHEME 1 Synthesis of chiral C60 fullerene bis-adducts by the Bingel reaction.
ABSOLUTE STEREOCHEMISTRY OF CHIRAL C60 FULLERENES
25

CHART 2 Chiral C60 fullerene bis-adducts and their absolute configurations.
1H NMR spectra of bis-adduct 10c exhibit 76 carbon
peaks and 14 proton signals, it has an asymmetric
structure [8]. To determine the absolute stereochem-
istry of chiral bis-adducts 10a and 10b, the 1H NMR
spectra of their tether parts were analyzed in detail.
Both compounds 10a and 10b are of C2-symmetry,
and therefore H-2 and H-20 protons are equivalent
( )-11 (Chart 3): 4.985 (2 H, d, J = 11.0 Hz,
H-1a, H-10a), 4.014 (2 H, dd, J = 11.0, 11.0 Hz,
H-1b, H-10b). Such chemical shift data clearly in-
dicate that the H-1a and H-10a protons of 10a are
syn to the ester carbonyl groups in the preferred con-
formation. Similar phenomenon was also observed
in the other diastereomer 10b: 5.235 (2 H, dd,
J = 11.3, 6.1 Hz, H-1a, H-10a), 4.160 (2 H, dd, J =
11.3, 3.1 Hz, H-1b, H-10b). Other important data to
deduce the preferred conformation of 10a are NOEs
observed between H-1a, H-10a protons (lower mag-
netic field) and OCH3 groups, which indicate that
those moieties are close to one another. In the case of
10b, other protons H-1b and H-10b (higher magnetic
field) showed NOEs with OCH3 groups.
1
to each other in H NMR spectra. To observe the
vicinal coupling constant between these two equiva-
lent protons, we have applied the 13C satellite band
0
method [9] and obtained J2,2 = 1.2 Hz for 10a and
J2,2 = 1.8 Hz for 10b. A remarkable point in the 1H
0
NMR spectrum of 10a is that methylene protons
(H-1a and H-10a) appear at a low magnetic field,
4.958 (2 H, dd, J = 10.1, 2.9 Hz), due to the
anisotropy effect of ester carbonyl group, while the
remaining methylene protons (H-1b and H-10b) are
at 4.225 (2 H, dd, J = 10.1, 9.7 Hz). The anisotropy
effect of ester carbonyl group was confirmed by ob-
serving a similar phenomenon in a model compound
The Karplus equation was next applied to the ob-
served coupling constants. Since one coupling con-
stant leads to four dihedral angles including plus and
minus signs, the combination of three observed vic-
inal coupling constants ( J = 9.7, 2.9, and 1.2 Hz)
26
K. YOSHIDA ET AL.

FIGURE 1 CD and UV spectra of chiral fullerene derivative [CD(+)281]-(S,S,fC )-10a in CH2ClCH2Cl.
FIGURE 2 CD and UV spectra of chiral fullerene derivative [CD( )281]-(S,S,fA)-10b in CH2ClCH2Cl.
ABSOLUTE STEREOCHEMISTRY OF CHIRAL C60 FULLERENES
27

FIGURE 3 CD and UV spectra of fullerene derivative [CD(+)310]-(S,S )-10c in CH2ClCH2Cl.
of 10a generates 43 = 64 possible conformers for
the tether part. By considering the four conditions,
(1) C2-symmetrical structure of 10a, (2) the (S,S ) ab-
solute configuration of two OCH3 groups, (3) syn
conformation of H-1a and H-10a protons to ester
carbonyl groups, and (4) NOEs between H-1a, H-10a
protons and OCH3 groups, all possible conforma-
tions were checked whether they fit the chiral (fC )
or (fA ) bis-adduct skeleton (C60/two cyclopropane
moieties) or not. These studies indicated that only
one conformer of (fC ) satisfies these conditions and
coupling constant data, and its absolute stereostruc-
ture is illustrated in Figure 4 (upper). Namely the ab-
solute stereochemistry of [CD(+)281]-10a was un-
ambiguously determined as (S,S,fC ). Similar studies
led to the conclusion that the other diastereomer
[CD( )281]-10b has the absolute stereochemistry
of (S,S,fA ) as shown in Figure 4 (lower).
Chiral bis-adduct [CD(+)281]-(S,S,fC)-10a was
treated with K2CO3 in EtOH/THF to yield tetra-
ethyl ester [CD(+)281]-(fC)-12 (29%), the 13C and
1H NMR spectra of which show 37 carbon peaks
and 5 proton signals, respectively [10] indicating its
C2-symmetrical structure (Scheme 2). The other chi-
ral bis-adduct of [CD( )281]-(S,S,fA)-10b was con-
verted to [CD( )281]-(fA)-12 (19%), the 13C and 1H
NMR spectra were identical with those of [CD(+)
281]-(fC)-12. The enantiomeric relation between
[CD(+)281]-(fC )-12 and [CD( )281]-(fA)-12 is
established by the CD spectra shown in Figure 5,
which are completely opposite to each other. Those
CD spectra are very similar in shape to those
of chiral bis-adduct [CD(+)281]-(S,S,fC)-10a and
CHART 3 Fullerene bis-adduct ( )-11 having an achiral
tether.
28
K. YOSHIDA ET AL.

FIGURE 4 Stable conformations of chiral fullerene bis-adducts (S,S,fC )-10a and (S,S,fA)-10b: most parts of C60 unit are omitted,
and methyl ester groups are shown instead of ethyl esters for the sake of simplicity.
[CD( )281]-(S,S,fA)-10b, concluding that CD spec-
tra of chiral C60 bis-adducts 10a, 10b, and 12 mainly
depend on their chiral -electron systems of C60
skeleton.
Major bis-adduct [CD(+)310]-(S,S )-10c was sim-
ilarly converted to tetra-ethyl ester 13 (23%), the 13C
and 1H NMR spectra of which show 39 carbon peaks
and 6 proton signals, respectively (Scheme 2) [11].
However it shows no CD reflecting its achiral Cs-
symmetrical structure.
of chiral C60 bis-adducts reflect mainly the absolute
stereostructure of their chiral -electron system of
fullerene skeleton, irrespective of the structure of
tether parts. In fact, the CD spectra of chiral bis-
adducts in Table 1 are similar to one another showing
a Cotton effect of medium intensity around 700 nm
and an intense Cotton effect of opposite sign around
280 nm. For example, the enantiomer 10a having
(fC) absolute configuration exhibits Cotton effects,
ext 696.0 nm (1ε 41.2) and 280.5 (+99.3). There-
fore it is concluded that (fC) enantiomer shows neg-
ative and positive CD Cotton effects around 700
and 280 nm, respectively, and therefore (fA) enan-
tiomer shows CD of opposite pattern. The CD data
In Table 1, the typical CD data and absolute con-
figurations of previously reported chiral bis-adducts
are listed together with those of [CD(+)281]-
(S,S,fC)-10a. As discussed above, the CD spectra
ABSOLUTE STEREOCHEMISTRY OF CHIRAL C60 FULLERENES
29

SCHEME 2 Conversion of chiral fullerene bis-adducts to tetra-ethyl esters.
FIGURE 5 CD and UV spectra of chiral fullerene derivative [CD(+)281]-(fC )-12 and [CD( )281]-(fA)-12 in CH2ClCH2Cl.
30
K. YOSHIDA ET AL.

TABLE 1 Reported CD spectral data and absolute configurations of chiral fullerene bis-adducts
Nakamura
et al.
Diederich
et al.
Nishimura
et al.
Shinkai
et al.
This study
Compound
Abs. config.
CD 1ε
(nm)
CD 1ε
10a
(S,S,fC)
41.2
696.0
+99.3
280.5
1
2
3
4
(R,R,fC)
+4.69
720.0
75.0
(S,S,fC)
37.0
(S,S,fA)
36.3
(fC), (fA)
+26.7
726.0
73.2
706.0
+89.0
281.0
737.0
+60.6
284.0
(nm)
288.0
287.0
of chiral bis-adduct (S,S,fC)-2 studied by Diederich
et al. agree with the present conclusion. However,
the CD data of bis-adducts (R,R,fC)-1 and (S,S,fA )-3
disagree with our conclusion, which implies that
their absolute configurations might be revised.
In conclusion, we have succeeded in the unam-
biguous determination of absolute configurations of
chiral C60 fullerene bis-adducts by intensive NMR
studies of two key diastereomers.
135.68, 139.03, 139.60, 140.49, 141.05, 141.05,
141.07, 141.44, 142.02, 142.21, 142.31, 143.62,
143.74, 144.21, 144.46, 144.53, 144.70, 144.84,
144.95, 145.02, 145.09, 145.34, 145.63, 145.67,
145.67, 146.48, 146.71, 162.75, 163.23; FAB-MS, calcd
for C76H22O10: 1094.1213. Found: 1094.1216.
[7] Bis-adduct [CD( )281]-(20S,30S,fA)-10b: 1H NMR
(600 MHz, CDCl3) 1.444 (6 H, t, J = 7.1 Hz), 3.441 (2 H,
dd, J = 6.1, 3.1 Hz), 3.579 (6 H, s), 4.160 (2 H, dd, J =
11.3, 3.1 Hz), 4.500 (2 H, dq, J = 10.7, 7.1 Hz), 4.530
(2 H, dq, J = 10.7, 7.1 Hz), 5.235 (2 H, dd, J = 11.3,
6.1 Hz); 13C satellite band, 1H NMR (600 MHz, CDCl3)
3.441 (0.02 H, dddd, J = 142.6, 6.1, 3.1, 1.8 Hz);
13C NMR (100 MHz, CDCl3) 14.23, 49.00, 58.93,
63.57, 65.41, 69.09, 71.50, 80.71, 130.25, 136.56,
138.41, 139.01, 140.92, 140.96, 141.01, 141.63,
141.68, 141.79, 142.26, 142.44, 143.60, 143.65,
144.43, 144.48, 144.58, 144.72, 144.75, 145.02,
145.02, 145.10, 145.10, 145.32, 145.64, 145.72,
146.44, 146.69, 162.48, 163.09; FAB-MS, calcd for
ACKNOWLEDGMENT
This work was supported in part by grants from the
Ministry of Education, Science, Sports, Culture, and
Technology, Japan/the Japan Society for the
Promotion of Science (Scientific Research (B)
No. 10554035, (B) No. 11480159, Priority Areas (A)
No. 10146205, (B) No. 10208202, and International
Joint No. 10045022 to N.H.).
C76H22O10: 1094.1213. Found: 1094.1233.
[8] Bis-adduct [CD(+)310]-(20S,30S)-10c: 1H NMR (600 MHz,
CDCl3) 1.388 (3 H, t, J = 7.1 Hz), 1.406 (3 H, t, J = 7.1
Hz), 3.286 (1 H, ddd, J = 6.8, 3.5, 1,8 Hz), 3.604 (3 H, s),
3.676 (3H, s), 3.779 (1 H, ddd, J = 8.0, 3.5, 1.6 Hz), 4.209
(1 H, dd, J = 11.4, 1.6 Hz), 4.394 (1 H, dq, J =
10.8, 7.1 Hz), 4.400 (1 H, dq, J = 10.7, 7.1 Hz),
4.476 (1 H, dq, J = 10.8, 7.1 Hz), 4.480 (1 H, dq,
J = 10.7, 7.1 Hz), 4.521 (1 H, dd, J = 11.6, 6.8 Hz), 4.733
(1 H, dd, J = 11.6, 1.8 Hz), 4.964 (1 H, dd, J = 11.4, 8.0
Hz); 13C NMR (100 MHz, CDCl3) 14.07, 14.19, 48.88,
49.08, 58.87, 58.93, 62.70, 63.38, 63.45, 63.64, 67.04,
67.09, 70.27, 70.29, 79.85, 80.27, 134.49, 136.84,
136.98, 137.66, 137.92, 138.19, 138.39, 139.12,
140.96, 141.06, 141.29, 141.34, 141.96, 142.35,
142.36, 142.39, 143.15, 143.20, 143.63, 143.67,
143.89, 144.00, 144.11, 144.28, 144.28, 144.29,
144.36, 144.44, 144.46, 144.66, 144.72, 144.75,
144.81, 145.05, 145.17, 145.22, 145.26, 145.29,
145.32, 145.34, 145.38, 145.41, 145.52, 145.69,
145.76, 145.92, 145.99, 146.02, 146.16, 146.22,
147.37, 147.46, 147.56, 147.56, 148.92, 150.04,
162.45, 162.75, 162.86, 162.96; FAB-MS, calcd for
REFERENCES
[1] E. Nakamura, H. Isobe, H. Tokuyama, and M. Sawamura,
J. Chem. Soc., Chem. Commun. 1996, 1747–1748.
[2] J.-F. Nierengarten, T. Habicher, R. Kessinger, F. Cardullo,
F. Diederich, V. Gramlich, J.-P. Gisselbrecht, C. Boudon,
and M. Gross, Helv. Chim. Acta 1997, 80, 2238–2267.
[3] H. Goto, N. Harada, J. Crassous, and F. Diederich,
J. Chem. Soc., Perkin Trans. 1998, 2, 1719–1723.
[4] (a) M. Taki, S. Sugita, Y. Nakamura, E. Kasashima,
E. Yashima, Y. Okamoto, and J. Nishimura, J. Am. Chem.
Soc. 1997, 119, 926–932; (b) M. Taki, Y. Nakamura,
H. Uehara, M. Sato, and J. Nishimura, Enantiomer 1998,
3, 231–239.
[5] T. Ishi-i, K. Nakashima, S. Shinkai, and A. Ikeda, J. Org.
Chem. 1999, 64, 984–990.
[6] Bis-adduct [CD(+)281]-(20S,30S,fC)-10a: 1H NMR
(600 MHz, CDCl3) 1.456 (6 H, t, J = 7.1 Hz), 3.435
(2 H, dd, J = 9.7, 2.9 Hz), 3.661 (6 H, s), 4.225 (2 H, dd,
J = 10.1, 9.7 Hz), 4.490 (2 H, dq, J = 10.7, 7.1 Hz),
4.541 (2 H, dq, J = 10.7, 7.1 Hz), 4.958 (2 H, dd, J =
10.1, 2.9 Hz); 13C satellite band, 1H NMR (600 MHz,
CDCl3) 3.435 (0.02 H, dddd, J = 142.8, 9.7, 2.9,
1.2 Hz); 13C NMR (100 MHz, CDCl3) 14.22, 48.89,
59.39, 61.32, 63.68, 69.12, 71.67, 75.47, 129.56,
C
76H22O10: 1094.1213. Found: 1094.1235.
[9] N. Harada, H.-Y. Li, N. Koumura, T. Abe, M. Watanabe,
and M. Hagiwara, Enantiomer, 1997, 2, 349–352.
[10] [CD(+)281]-(fC)-12: 1H NMR (400 MHz, CDCl3) 1.433
(6 H, t, J = 7.1 Hz), 1.435 (6 H, t, J = 7.1 Hz), 4.416
(2 H, dq, J = 10.7, 7.1 Hz), 4.467 (2 H, dq, J = 10.7,
7.1 Hz), 4.493 (4 H, q, J = 7.1 Hz); 13C NMR (100 MHz,
ABSOLUTE STEREOCHEMISTRY OF CHIRAL C60 FULLERENES
31

CDCl3)
14.10, 14.19, 48.78, 63.07, 63.23, 69.27,
(6 H, t, J = 7.1 Hz), 4.403 (2 H, dq, J = 10.8,
7.1 Hz), 4.435 (2 H, dq, J = 10.8, 7.1 Hz), 4.454
(2 H, dq, J = 10.6, 7.1 Hz), 4.510 (2 H, dq, J = 10.6,
7.1 Hz); 13C NMR (100 MHz, CDCl3) 14.10, 14.13,
49.46, 63.11, 63.14, 67.80, 70.50, 134.97, 136.94,
137.37, 138.41, 139.65, 141.07, 141.28, 142.47,
142.82, 143.36, 143.59, 143.69, 144.22, 144.28,
144.37, 144.55, 144.67, 145.04, 145.22, 145.28,
145.37, 145.73, 145.82, 145.89, 145.94, 146.20,
147.27, 147.38, 147.45, 148.66, 163.05, 163.47;
71.87, 130.93, 137.81, 138.21, 138.55, 140.73, 141.00,
141.60, 141.84, 141.99, 142.26, 142.39, 142.54,
143.42, 143.61, 144.25, 144.41, 144.41, 144.44,
144.69, 144.81, 144.99, 145.12, 145.16, 145.27,
145.48, 145.60, 146.39, 146.62, 162.96, 163.74; UV-
Vis (ClCH2CH2Cl)
(102,000); CD (ClCH2CH2Cl)
316.5 nm (ε 35,200), 255.5
max
700.5 nm (1ε 37.0),
ext
486.5 (+23.0), 378.0 ( 26.2), 338.5 (+60.9), 280.5
(+98.3), 262.0 ( 146.1); FAB-MS, calcd for C74H20O8:
1036.1158. Found: 1036.1161.
UV-Vis (ClCH2CH2Cl)
321.5 nm (ε 34,500), 259.5
max
[11] Achiral tetra-ethyl ester 13: 1H NMR (400 MHz,
(111,000); APCI-MS, calcd for C74H20O8: 1036.1158.
Found: 1036.1158.
CDCl3)
1.389 (6 H, t,
J
=
7.1 Hz), 1.457
32
K. YOSHIDA ET AL.