Optically active telluronium imides: Optical resolution, absolute configuration, and mechanism of racemization

Article abstract of DOI:10.1002/hc.10185

Thermodynamically and kinetically stabilized asymmetric diaryltelluronium imides were synthesized and optically resolved into their enantiomers on an optically active column using medium-pressure column chromatography. The relationship between the absolut

Full text of DOI:10.1002/hc.10185

Heteroatom Chemistry
Volume 14, Number 6, 2003
Optically Active Telluronium Imides:
Optical Resolution, Absolute Configuration,
and Mechanism of Racemization
Toshio Shimizu, Yoshito Machida, and Nobumasa Kamigata
Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University,
Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
Received 27 February 2003
synthetic course via telluronium imides has been re-
ABSTRACT: Thermodynamically and kinetically sta-
ported to show higher optical yields than that via
bilized asymmetric diaryltelluronium imides were
the corresponding selenonium imides. However, to
synthesized and optically resolved into their enan-
our knowledge, there had been no report concern-
tiomers on an optically active column using medium-
ing the isolation of optically active selenonium and
pressure column chromatography. The relationship
telluronium imides, probably because selenonium
between the absolute configuration and the op-
and telluronium imides are unstable toward hydrol-
tical properties of the chiral telluronium imides
ysis. Recently, we reported the isolation of optically
was clarified. The mechanism of the racemization,
active selenonium imides and clarified their stere-
which involves the formation of telluroxides by
ochemistry and configurational stabilities [8,9]. On
the hydrolysis of the telluronium imides, was pro-
the other hand, telluronium imides are considered to
ꢀ
C
posed. 2003 Wiley Periodicals, Inc. Heteroatom Chem
be much more unstable toward hydrolysis [10] than
the corresponding selenonium imides, and few com-
pounds have been synthesized even in their racemic
14:523–529, 2003; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.10185
form [10,11]. Therefore, optically active telluronium
imides have not yet been isolated so far. An electron-
INTRODUCTION
withdrawing group on the nitrogen atom is known to
stabilize telluronium imides [11]. We successfully
synthesized telluronium imides that were stabilized
not only thermodynamically with an electron-with-
drawing group on the nitrogen atom but also kineti-
cally with bulky substituents on the tellurium atom,
and attempted to resolve them into their optical
isomers. We report herein the optical resolution of
asymmetric telluronium imides, the absolute config-
uration, and mechanism of their racemization [12].
Many chiral tricoordinate sulfur compounds are
known and used as chiral sources in asymmetric
synthesis [1]. Some optically active tricoordinate se-
lenium and tellurium compounds have also been
isolated, and their properties and applicability to
asymmetric reactions have been studied [2–5]. Op-
tically active selenonium [6] and telluronium imides
[7] have also been applied to asymmetric synthe-
sis as important transient intermediates, and the
RESULTS AND DISCUSSION
Correspondence to: Nobumasa Kamigata; e-mail: kamigata-
nobumasa@c.metro-u.ac.jp.
Contract grant sponsor: Ministry of Education, Science, Sports,
Preparation of Racemic Telluronium Imides
Mesityl 2,4,6-triisopropylphenyltelluronium N-
toluene-4ꢁ-sulfonimide (1) was synthesized by
and Culture, Japan.
c
ꢀ
2003 Wiley Periodicals, Inc.
523

524 Shimizu, Machida, and Kamigata
reacting the corresponding telluroxide, which was
prepared by oxidation of telluride with tert-butyl
hypochlorite [13], with toluene-4-sulfonamide in the
presence of molecular sieves in 97% yield, as shown
in Scheme 1. Similarly, bulkier telluronium N-
toluene-4-sulfonimide 2 was obtained in 89% yield.
However, a less bulky telluronium imide, phenyl
2,4,6-triisopropylphenyltelluronium N-toluene-4ꢁ-
sulfonimide, could not be isolated because of facile
hydrolysis although its formation was confirmed by
1H NMR measurement of the reaction mixture. Tel-
luronium N-trifluoromethanesulfonimide 3 was syn-
thesized by reacting the corresponding telluroxide
with trifluoromethanesulfonamide in the presence
of sodium sulfate in 86% yield. In a similar reaction,
telluronium N-trifluoromethanesulfonimide pos-
sessing a 2,4,6-tri-tert-butylphenyl group 4 could be
obtained in 92% yield, whereas phenyl 2,4,6-tri-tert-
butylphenyltelluronium N-toluene-4ꢁ-sulfonimide
could not be synthesized because the reaction failed
to proceed due to steric hindrance.
corresponding telluroxide was observed. When 2-
propanol was used as the mobile phase, a peak cor-
responding to toluene-4-sulfonamide was also de-
tected. These results indicate that 1 was hydrolyzed
in the column despite careful purification of the sol-
vents. In the case of telluronium imide with a bulkier
substituent 2, two peaks corresponding to each of
the enantiomers of 2 were observed, as shown in
Fig. 1. This result clearly indicates that changing the
alkyl substituents on one of the benzene rings from
methyl to ethyl group is very effective for stabilizing
the telluronium imides toward the hydrolysis. Sim-
ilarly, telluronium N-trifluoromethanesulfonimides
3 and 4 could also be optically resolved into their
respective enantiomers.
The optical resolution of telluronium imides 2,
3, and 4 was carried out on a preparative scale using
the same type of chiral column. As a result, optically
pure telluronium imides (+)-2, (+)-3, and (+)-4 were
obtained from the respective first fractions that were
eluted, as shown in Table 1, and their optical puri-
ties were confirmed by HPLC. Optically active (−)-
isomers (−)-2, (−)-3, and (−)-4 were also obtained in
the optically pure form from the second-eluted por-
tions by repeated chromatographic separations.
Optical Resolution of Telluronium Imides
Telluronium imide
1 was subjected to high-
performance liquid chromatography (HPLC) on an
analytical scale by using an optically active column
packed with cellulose carbamate derivative/silica gel
and hexane/2-propanol (95/5) as the mobile phase.
However, no peak corresponding to the telluronium
imide was detected, whereas a peak assigned to the
Circular Dichroism Spectra and
Absolute Configuration of Optically Active
Telluronium Imides
The circular dichroism spectra of optically ac-
tive telluronium imides (+)-2, (+)-3, and (+)-4
O
NTs
Te
Te
TsNH2, MS (3A)
C6H6, reflux
1
NTs
Te
TsNH2, MS (3A)
C6H6, reflux
O
Te
2
NTf
Te
TfNH2, Na2SO4
CH2Cl2, r.t.
3
O
NTf
Te
TfNH2, Na2SO4
CH2Cl2, r.t.
Te
FIGURE 1 Optical resolution of telluronium imides 1–4 on
an optically active column packed with cellulose carbamate
derivative/silica gel (Daicel Chiralcel OD; 4.6 × 250 mm) by
HPLC on an analytical scale at 25◦C. (a) hexane/2-propanol
(95/5); (b) hexane/2-propanol (90/10); (c) hexane/2-propanol
(98/2); (d) hexane/2-propanol (97/3).
4
SCHEME 1

Optically Active Telluronium Imides 525
TABLE 1 Optical Resolution and Specific Rotation of Telluronium Imides 2–4a
First Enantiomer
Second Enantiomer
Compound
2-Propanol (%)b
[α]D (c)c
ee (%)
[α]D (c)c
ee (%)
2
3
4
10
2
3
+55.0 (0.44)
+79.0 (0.52)
+57.6 (0.085)
100
100
100
−53.2 (0.65)
−82.3 (0.20)
−61.0 (0.050)
100
100
100
aOptical resolution was carried out on an optically active column packed with cellulose carbamate derivative/silica gel (Daicel Chiralcel OD;
10× 250 mm) by HPLC on a preparative scale at 25◦C.
bVolume percentage of 2-propanol in hexane used as mobile phase.
cSpecific rotations were taken in acetonitrile at 25◦C.
showed positive first Cotton effects in acetoni-
trile at 285, 286, and 293 nm, respectively, and
(−)-2, (−)-3, and (−)-4 showed negative first Cot-
ton effects in the corresponding regions, as de-
picted in Fig. 2. Those first Cotton effects showed
good agreement with those of the optically ac-
tive selenium analogue; the spectrum of (R)-
(+)-phenyl 2,4,6-tri-tert-butylphenylselenonium N-
toluene-4ꢁ-sulfonimide (R)-(+)-5 showed a positive
first Cotton effect at 272 nm, and that of the (S)-(−)-
isomer showed a negative first Cotton effect, the ab-
solute configuration of which has been clearly char-
acterized by X-ray crystallographic analysis of the
(−)-isomer [9]. Based on a comparison of the optical
properties, the absolute configuration of telluronium
imides (+)-2, (+)-3, and (+)-4 was assigned to the R-
form and that of (−)-2, (−)-3, and (−)-4 to the S-form.
Configurational Stability and Mechanism of
Racemization of Optically Active Telluronium
Imides
Optically active telluronium imide (R)-(+)-2 was sta-
ble in the solid state under nitrogen; however, racem-
ization was observed in solution. The decrease in
the optical purity of (R)-(+)-2 showed a good lin-
ear relationship with the first-order rate plots in
chloroform that had been freshly distilled from cal-
cium hydride, at 25◦C (k = 6.67 × 10−6 s−1; t1/2
=
28.9 h). Racemization was also observed in care-
fully dried acetonitrile at 25◦C (k = 5.00 × 10−6 s−1;
t1/2 = 38.5 h). Pyramidal inversion is one possible
mechanism of the racemization. However, the bar-
rier for the pyramidal inversion of telluronium imide
has been calculated to be higher than those for the
pyramidal inversion of the corresponding sulfur and
selenium analogues; the pyramidal inversion ener-
gies for model molecules, dimethylchalcogen-onium
N-trifluoromethanimides, are 34.4 (chalcogen = S),
44.3 (chalcogen = Se), and 54.4 (chalcogen = Te) kcal
mol−1 [14]. Therefore, racemization via the pyra-
midal inversion process seems unlikely, at least at
room temperature. Edge inversion is also a possible
mechanism of the racemization [15]; however, this
is improbable because the structure of the transition
NTs
Se
2
Ar
1
Ar
1
Ar = C H
6
5
2
Ar = 2,4,6-(t-Bu) C H
3
6
2
5
(R)-(+)-
FIGURE 2 Circular dichroism spectra of optically active telluronium imides 2–4 in acetonitrile with UV spectra of their racemic
samples.

526 Shimizu, Machida, and Kamigata
state is not favored because of the presence of bulky
substituents.
On the other hand, telluronium imides are
easily hydrolyzed to give the corresponding tel-
luroxides and amines [11]. When a CDCl3 solution
of racemic telluronium imide 2 and phenyl 2,4,6-
triisopropylphenyl telluroxide (6) was stored at
room temperature, both 2,4,6-triethylphenyl 2ꢁ,4ꢁ,6ꢁ-
triisopropylphenyl telluroxide (7) and phenyl
2,4,6-triisopropylphenyltelluronium N-toluene-4ꢁ-
sulfonimide (8) were found together with the starting
materials (Scheme 2). Furthermore, a CDCl3 solu-
tion of phenyl 2,4,6-tri-tert-butylphenyl telluroxide
and trifluoromethanesulfonamide yielded telluro-
nium imide 4 together with the starting materials
at room temperature even without sodium sulfate.
These results indicate that telluronium imides and
telluroxides exist in equilibrium through hydrolysis
of the imides and imination of the oxides. We
previously clarified that optically active telluroxides
readily racemize in the presence of a trace amount
of water remaining in the solvent despite careful
purification [13,16]. Therefore, the mechanism
involving the corresponding telluroxides, which
are formed in situ by hydrolysis of the telluronium
imides, is the most plausible for the racemization of
telluronium imides.
When optically active telluronium imide (R)-(+)-
4 was stored in acetonitrile (3.3 × 10−5 M) containing
a large excess (65 equiv) of 1 N NaOH solution, Cot-
ton effects corresponding to optically active tellurox-
ide (R)-(+)-9 [13] appeared immediately with a de-
crease in that of (R)-(+)-4 (Fig. 3), whereas no Cotton
effect for the telluroxide was observed when (R)-(+)-
4 was hydrolyzed under neutral conditions, probably
because racemization of the resulting telluroxide oc-
curred more rapidly than hydrolysis of the imide un-
der neutral conditions. Under acidic conditions, de-
composition of the telluronium imide was observed.
FIGURE 3 Hydrolysis of optically active telluronium imide
(R)-(+)-4 under basic conditions.
Since the stereochemistry of the resulting tellurox-
ide formed under basic conditions was R [13,16],
the hydrolysis of telluronium imides proceeds with
a retention of stereochemistry, at least under basic
conditions. This result differs from that with sulfo-
nium imide: sulfonium imides are known to be hy-
drolyzed with an inversion of stereochemistry under
basic conditions [17]. This difference in the mech-
anism of hydrolysis may be due to the ease of the
formation of hypervalent tellurane as an intermedi-
ate compared with that of sulfurane.
A plausible mechanism for the racemization of
telluronium imides under basic conditions is shown
in Scheme 3. The addition of water to the opti-
cally active telluronium imide from the side oppo-
site the bulkiest substituent (Ar2) gives tellurane 10
catalyzed by OH− under basic conditions. Telluranes
10 and 11 exist in equilibrium. Elimination of amide
from the tellurane yields telluroxide 12 with a reten-
tion of stereochemistry, which then racemizes via an
achiral hydrate [13,16]. Imination of the resulting
racemized telluroxide gives the racemic telluronium
imide.
O
Te
+
2
CDCl3, r.t.
6
O
NTs
Te
Te
+
CONCLUSION
Kinetically and thermodynamically stabilized tel-
luronium imides were synthesized by reacting the
corresponding telluroxides with amides. Optically
7
8
SCHEME 2

Optically Active Telluronium Imides 527
SCHEME 3
active telluronium imides were isolated by chro-
matographic resolution on a chiral column. The rela-
tionship between the absolute configuration and the
optical properties was clarified by comparison with
that of optically active selenonium imides, which
was previously determined by us. The mechanism of
the racemization involving the formation of hyper-
valent tellurane and telluroxide was also proposed.
solution was concentrated under reduced pressure
to give telluronium imide (1: 97%; 2: 89%). Further
purification was not carried out to prevent the hy-
drolysis during the handling.
Mesityl
2,4,6-Triisopropylphenyltelluronium
Toluene-4ꢁ-sulfonimide
(rac-1). mp
156–157◦C
1
(colorless solid). H NMR (500 MHz, CDCl3) δ 0.94
(d, 6H, J = 6.7 Hz), 1.12 (d, 6H, J = 6.7 Hz), 1.23
(d, 6H, J = 6.7 Hz), 2.25 (s, 3H), 2.31 (s, 3H), 2.45
(s, 6H), 2.86 (sep, 1H, J = 6.7 Hz), 3.45 (sep, 2H,
J = 6.7 Hz), 6.83 (s, 2H), 7.03 (s, 2H), 7.07 and 7.68
(ABq, 4H, J = 8.1 Hz); 13C NMR (125 MHz, CDCl3)
δ 20.8, 21.3, 22.4, 23.6, 23.7, 24.3, 24.6, 34.1, 34.9,
124.0, 125.7, 126.1, 127.7, 128.7, 131.1, 140.1, 141.5,
142.5, 143.9, 153.2, 153.5; 125Te NMR (158 MHz,
CDCl3) δ 991.0; IR (KBr) νmax 3000–2760, 1590,
1560, 1460, 1380, 1270, 1125, 1020, 940, 845, 810,
740, 675, 565, 550 cm−1; UV (MeCN) λmax 209 (ε
4.6 × 104), 242 (ε 3.3 × 104), 286 (sh, ε 5.5 × 103) nm;
MS m/z 621 (130Te, M+), 619 (128Te, M+), 452, 203,
119; HRMS calcd for C31H41NO2S130Te 621.1925,
found 621.1900.
EXPERIMENTAL
Hexane and benzene were distilled from sodium
metal before use. Chloroform, dichloromethane, and
2-propanol were freshly distilled from calcium hy-
dride. Acetonitrile was distilled from phosphorus(V)
oxide before use. All reactions were carried out un-
der nitrogen.
Preparation of Diaryl Telluroxides
Phenyl 2,4,6-triisopropylphenyl telluroxide [16],
mesityl 2,4,6-triisopropylphenyl telluroxide [13],
2,4,6-triethylphenyl 2ꢁ,4ꢁ,6ꢁ-triisopropylphenyl tellur-
oxide, and phenyl 2,4,6-tri-tert-butylphenyl tellurox-
ide [13] were prepared from corresponding tellurides
by oxidation with tert-butyl hypochlorite in 69, 81,
62, and 86% yields, respectively [13].
2,4,6-Triethylphenyl 2ꢁ,4ꢁ,6ꢁ-Triisopropylphenyltell-
uronium Toluene-4ꢁꢁ-sulfonimide (rac-2). Colorless
viscous oil. 1H NMR (500 MHz, CDCl3) δ 0.96 (d, 6H,
J = 6.7 Hz), 1.01 (t, 6H, J = 7.6 Hz), 1.09 (d, 6H,
J = 6.7 Hz), 1.17 (t, 3H, J = 7.6 Hz), 1.21 (d, 6H,
J = 6.7 Hz), 2.31 (s, 3H), 2.57 (q, 2H, J = 7.6 Hz),
2.75–2.97 (m, 5H), 3.49 (sep, 2H, J = 6.7 Hz), 6.92
(s, 2H), 7.02 (s, 2H), 7.07 and 7.69 (ABq, 4H, J =
8.1 Hz); 13C NMR (125 MHz, CDCl3) δ 15.4, 15.7, 21.3,
23.7, 24.3, 24.6, 28.5, 28.7, 34.1, 34.7, 124.1, 125.8,
Synthesis of Diaryl Telluronium
Toluene-4-sulfonimides (rac-1 and 2)
Typically, a benzene solution (100 ml) of telluroxide
(3.0 mmol) and toluene-4-sulfonamide (3.0 mmol)
was refluxed for 12 h equipped with a Dean-Stark
condenser including molecular sieves 3A (5 g). The

528 Shimizu, Machida, and Kamigata
126.5, 128.3, 128.7, 128.8, 140.0, 144.0, 148.0, 148.7,
153.1, 153.3; 125Te NMR (158 MHz, CDCl3) δ 992.2;
IR (neat) νmax 3000–2700, 1590, 1560, 1460, 1260,
1125, 1080, 925, 670, 565, 550 cm−1; UV (MeCN)
λmax 242 (ε 4.0 × 104), 285 (sh, ε 7.8 × 103) nm; MS
m/z 663 (130Te, M+), 661 (128Te, M+), 494, 203, 161;
HRMS calcd for C34H47NO2S130Te 663.2390, found
663.2362.
Optical Resolution of Racemic Telluronium
Imides by Means of Medium-Pressure Liquid
Chromatography Using an Optically Active
Column
Typical procedure for optical resolution of telluro-
nium imides: Racemic telluronium imide (20 mg)
in eluent (0.3 ml) was applied to an optically ac-
tive column packed with cellulose carbamate deriva-
tive/silica gel (Daicel Chiralcel OD; 10 × 250 mm)
and eluted with hexane containing 10 (for 2), 2 (for
3), and 3 (for 4) vol% 2-propanol at a flow rate of 1.5
for 2 and 1.0 ml min−1 for 3 and 4. About 6 mg of
each optically active telluronium imide was collected
from the first and second eluates, respectively. In the
case of 2, optically pure (+)- and (−)-telluronium
imides were obtained by the above procedure. With 3
and 4, each eluate was subjected to chromatographic
resolution again to give the optically pure telluro-
nium imide. Their optical purities were determined
by HPLC analysis using the same type of chiral col-
umn (4.6 × 250 mm) at an analytical scale.
Synthesis of Diaryl Telluronium
Trifluoromethanesulfonimides (rac-3 and 4)
Typically, a dichloromethane solution (20 ml) of
telluroxide (1.0 mmol) and trifluoromethanesulfon-
amide (1.0 mmol) was stirred for desired period (3:
12 h; 4: 1.5 h) in the presence of sodium sulfate
(6 g) at room temperature. The solution was concen-
trated under reduced pressure to give telluronium
imide (3: 86%; 4: 92%). Further purification was
not carried out to prevent the hydrolysis during the
handling.
2,4,6-Triethylphenyl 2ꢁ,4ꢁ,6ꢁ-Triisopropylphenyltell-
uronium Trifluoromethanesulfonimide (rac-3). Col-
orless viscous oil. 1H NMR (500 MHz, CDCl3) δ 1.03
(d, 6H, J = 6.6 Hz), 1.10 (t, 6H, J = 7.5 Hz), 1.18–
1.24 (m, 15H), 2.61 (q, 2H, J = 7.5 Hz), 2.75–3.01
(m, 5H), 3.44 (sep, 2H, J = 6.6 Hz), 6.99 (s, 2H),
7.09 (s, 2H); 13C NMR (125 MHz, CDCl3) δ 15.2, 15.7,
23.6, 24.4, 28.4, 28.8, 34.1, 35.3, 119.3, 121.9, 124.6,
125.2, 128.9, 148.6, 148.7, 153.2, 153.9; 125Te NMR
(158 MHz, CDCl3) δ 1028.6; IR (neat) νmax 3000–2800,
1590, 1560, 1460, 1290, 1180, 1125, 1080, 988, 610,
570, 515 cm−1; UV (MeCN) λmax 206 (ε 5.5 × 104),
249 (ε 1.9 × 104), 287 (sh, ε 3.7 × 103) nm; MS m/z
641 (130Te, M+), 639 (128Te, M+), 494, 203, 161. Anal.
Calcd for C28H40F3NO2S130Te: C, 52.61; H, 6.31; N,
2.19. Found: C, 52.61; H, 6.32; N, 2.10.
Compound (R)-(+)-2. Colorless viscous oil;
100% ee; [α]D +55.0 (c 0.44, MeCN); CD (MeCN)
λmax 248 ([θ] + 9.0 × 103), 285 ([θ] + 4.6 × 103) nm.
1H and 13C NMR spectra were almost same with
those of racemic one.
Compound (S)-(−)-2. Colorless viscous oil;
100% ee; [α]D −53.2 (c 0.65, MeCN); CD (MeCN) λmax
249 ([θ] − 9.8 × 103), 285 ([θ] − 4.8 × 103) nm. 1H and
13C NMR spectra were almost same with those of
racemic one.
Compound (R)-(+)-3. Colorless viscous oil;
100% ee; [α]D +79.0 (c 0.52, MeCN); CD (MeCN)
λmax 208 ([θ] + 4.4 × 104), 218 ([θ] + 7.9 × 103), 234
([θ] + 3.4 × 104), 252 ([θ] − 1.6 × 104), 286 ([θ] +
1.4 × 104) nm. 1H and 13C NMR spectra were almost
same with those of racemic one.
Phenyl 2,4,6-Tri-tert-butylphenyltelluronium Tri-
fluoromethanesulfonimide (rac-4). mp 127–128◦C
(decomp, colorless prisms from dichloromethane);
1H NMR (500 MHz, CDCl3) δ 1.36 (s, 9H), 1.45 (s,
18H), 6.99–7.00 (m, 2H), 7.34–7.44 (m, 3H), 7.58
(s, 2H); 13C NMR (125 MHz, CDCl3) δ 30.9, 33.6,
35.2, 39.3, 119.4, 122.0, 125.6, 126.2, 130.1, 131.7,
133.4, 154.6, 157.9; 125Te NMR (158 MHz, CDCl3) δ
1069.0; IR (KBr) νmax 3000–2800, 1585, 1530, 1477,
1440, 1400, 1370, 1300, 1200, 1160, 1120, 975, 740,
690, 610, 570, 515 cm−1; UV (MeCN) λmax 223 (sh,
ε 2.2 × 104), 238 (sh, ε 1.6 × 104), 268 (sh, ε 8.3 ×
103), 293 (sh, ε 3.8 × 103) nm; MS m/z 599 (130Te,
M+), 597 (128Te, M+), 452, 245, 77; HRMS calcd for
C25H34F3NO2S130Te 599.1325, found 599.1302.
Compound (S)-(−)-3. Colorless viscous oil;
100% ee; [α]D −82.3 (c 0.20, MeCN); CD (MeCN)
λmax 206 ([θ] − 5.2 × 104), 219 ([θ] − 8.2 × 103), 234
([θ] − 3.2 × 104), 253 ([θ] + 1.5 × 104), 286 ([θ] −
1.3 × 104) nm. 1H and 13C NMR spectra were almost
same with those of racemic one.
Compound (R)-(+)-4. Colorless viscous oil;
100% ee; [α]D +57.6 (c 0.085, MeCN); CD (MeCN)
λmax 220 ([θ] − 3.9 × 104), 237 ([θ] + 1.0 × 104), 247
([θ] + 6.7 × 103), 268 ([θ] + 1.1 × 104), 278 ([θ] +
9.5 × 103), 293 ([θ] + 1.3 × 104) nm. 1H and 13C NMR
spectra were almost same with those of racemic one.

Optically Active Telluronium Imides 529
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Compound (S)-(−)-4. Colorless viscous oil;
100% ee; [α]D −61.0 (c 0.050, MeCN); CD (MeCN)
λmax 222 ([θ] + 3.8 × 104), 238 ([θ] − 1.2 × 104), 253
([θ] − 5.7 × 103), 267 ([θ] − 1.1 × 104), 278 ([θ] −
9.0 × 103), 293 ([θ] − 1.3 × 104) nm. 1H and 13C NMR
spectra were almost same with those of racemic one.
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