Isolation of stable enantiomerically pure telluroxides and their stereochemistry

Article abstract of DOI:10.1021/jo991721n

Optical resolution of kinetically and thermodynamically stabilized diaryl telluroxides possessing bulky substituents (rac-1a-d) and amino group (rac-2a-c), respectively, by liquid chromatography using optically active columns yielded stable enantiomerically pure telluroxides. The absolute configurations of the optically active telluroxides were determined by comparing their specific rotations and CD spectra with those of sulfur or selenium analogues. The kinetics for the racemization of optically active telluroxides in solution was studied, and it was found that kinetic and thermodynamic stabilization were very effective preventing the racemization of telluroxides. The stabilization energy of telluroxides by intramolecular coordination of the amino group to the tellurium atom was estimated to be ca. 5 kcal mol^-1 by variable temperature ¹H NMR measurement. The mechanism for the racemization of optically active telluroxides was studied by an isotope experiment using H₂¹⁸O, and the results indicated that optically active telluroxides underwent racemization via an achiral tetracoordinated hydrate.

Full text of DOI:10.1021/jo991721n

J . Org. Chem. 2000, 65, 2127-2133
2127
Isola tion of Sta ble En a n tiom er ica lly P u r e Tellu r oxid es a n d Th eir
Ster eoch em istr y
Hideo Taka, Yuko Yamazaki, Toshio Shimizu, and Nobumasa Kamigata*
Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minami-ohsawa,
Hachioji, Tokyo 192-0397, J apan
Received November 4, 1999
Optical resolution of kinetically and thermodynamically stabilized diaryl telluroxides possessing
bulky substituents (rac-1a -d ) and amino group (rac-2a -c), respectively, by liquid chromatography
using optically active columns yielded stable enantiomerically pure telluroxides. The absolute
configurations of the optically active telluroxides were determined by comparing their specific
rotations and CD spectra with those of sulfur or selenium analogues. The kinetics for the
racemization of optically active telluroxides in solution was studied, and it was found that kinetic
and thermodynamic stabilization were very effective preventing the racemization of telluroxides.
The stabilization energy of telluroxides by intramolecular coordination of the amino group to the
tellurium atom was estimated to be ca. 5 kcal mol-1 by variable temperature 1H NMR measurement.
The mechanism for the racemization of optically active telluroxides was studied by an isotope
experiment using H218O, and the results indicated that optically active telluroxides underwent
racemization via an achiral tetracoordinated hydrate.
In tr od u ction
optically pure alkyl aryl selenoxide had not been isolated
until recently because optically active alkyl aryl selenox-
ides undergo racemization more rapidly than diaryl
selenoxides.9b Fortunately, there is another technique for
stabilizing molecular structures, i.e., thermodynamic
stabilization by an electronic effect or coordination of
intramolecular substituents, and there are many reports
concerning stabilization through the intramolecular co-
ordination of amino groups.10 We previously reported the
preparation of alkyl aryl selenoxides possessing an amino
group, and the isolation of optically pure alkyl aryl
selenoxides by chromatographic resolution using a chiral
stationary phase.11
Recently, our studies have focused on the synthesis and
stereochemistry of optically active selenium and tel-
lurium compounds.1-3 Among tricoordinated optically
active selenium and tellurium compounds, it had been
thought that optically active selenoxides and telluroxides
are too difficult to isolate because the racemization was
estimated to be very rapid. Since the first synthesis of
an optically active selenoxide (11% ee), stabilized against
racemization by bulky substituents on the selenium
atom, was reported by Davis et al. in 1983,4 there have
been several reports on the synthesis of optically active
selenoxides, by means of optical resolution using frac-
tional recrystallization of diastereomeric mixtures,5 com-
plexation with a chiral ligand,6 chromatographic resolu-
tion of racemic mixtures using an optically active columns,7
and asymmetric oxidation of selenides.8,9 We first isolated
an optically pure diaryl selenoxide (100% ee) that was
stabilized by bulky substituents in 1986;5 however, an
On the other hand, optically active telluroxides have
not yet been isolated because they undergo racemization
even more rapidly than optically active selenoxides,
although optically active telluroxides have been proposed
as intermediates in asymmetric reactions by Uemura et
al.12 We designed and synthesized configurationally
stable telluroxides using two stabilizing methods; one is
kinetic stabilization by bulky substituents13 and the other
is thermodynamic stabilization by the intramolecular
coordination of the amino group to the tellurium atom
and succeeded to resolve these racemic compounds into
enantiomerically pure form by means of HPLC using a
chiral stationary phase. The absolute configurations of
the optically active telluroxides were determined on the
basis of their specific rotations and CD spectra, and the
* To whom correspondence should be addressed. Tel: +81 (426) 77-
2556. Fax: +81 (426) 77-2525. E-mail: kamigata-nobumasa@c.metro-
u.ac.jp.
(1) For review, see: Kamigata, N.; Shimizu, T. Rev. Heteroatom
Chem. 1991, 4, 226.
(2) For review, see: Shimizu, T.; Kamigata, N. Org. Prep. Proced.
Int. 1997, 29, 603.
(3) For review, see: Shimizu, T.; Kamigata, N. Rev. Heteroatom
Chem. 1998, 18, 11.
(4) Davis, F. A.; Billmers, J . M.; Stringer, O. D. Tetrahedron Lett.
1983, 24, 3191.
(5) (a) Shimizu, T.; Kobayashi, M. Chem. Lett. 1986, 161. (b)
Shimizu, T.; Kikuchi, K.; Ishikawa, Y.; Ikemoto, I.; Kobayashi, M.;
Kamigata, N. J . Chem. Soc., Perkin Trans. 1 1989, 597.
(6) Toda, F.; Mori, K. J . Chem. Soc., Chem. Commun. 1986, 1357.
(7) (a) Shimizu, T.; Kobayashi, M. Bull. Chem. Soc. J pn. 1986, 59,
2654. (b) Shimizu, T.; Kobayashi, M. J . Org. Chem. 1987, 52, 3399.
(8) (a) Kobayashi, M.; Ohkubo, H.; Shimizu, T. Bull. Chem. Soc. J pn.
1986, 59, 503. (b) Shimizu, T.; Kobayashi, M.; Kamigata, N. Sulfur
Lett. 1988, 8, 61. (c) Shimizu, T.; Kobayashi, M.; Kamigata, N. Bull.
Chem. Soc. J pn. 1989, 62, 2099.
(10) (a) Sadekov, I. D.; Maksimenko, A. A.; Maslakov, A. G.; Minkin,
V. I. J . Organomet. Chem. 1990, 391, 179. (b) Yoshifuji, M.; Sangu, S.;
Kamijo, K.; Toyota, K. Chem. Ber. 1996, 129, 1049. (c) Belzner, J .;
Schar, D.; Herbst-Irmer, R.; Kneisel, B. O.; Noltemeyer, M. Tetrahedron
1998, 54, 8481. (d) Mugesh, G.; Singh, H. B.; Butcher, R. J . Tetrahedron
Asymmetry 1999, 10, 237.
(11) Shimizu, T.; Enomoto, M.; Taka, H.; Kamigata, N. J . Org. Chem.
1999, 64, 8242.
(12) Chiba, T.; Nishibayashi, Y.; Singh, J . D.; Ohe, K.; Uemura, S.
Tetrahedron Lett. 1995, 36, 1519.
(9) (a) Davis, F. A.; Stringer, O. D.; McCauley, J . P., J r. Tetrahedron
1985, 41, 4747. (b) Davis, F. A.; Reddy, R. T. J . Org. Chem. 1992, 57,
2599.
(13) Preliminary communication: Shimizu, T.; Yamazaki, Y.; Taka,
H.; Kamigata, N. J . Am. Chem. Soc. 1997, 119, 5966.
10.1021/jo991721n CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/03/2000

2128 J . Org. Chem., Vol. 65, No. 7, 2000
Taka et al.
Sch em e 1
configurational stability of optically active telluroxides
was studied.
Resu lts a n d Discu ssion
Previously, we isolated optically pure selenoxide that
was stabilized against the racemization by bulky sub-
stituents.5 Optically active telluroxides have been pre-
sumed to undergo racemization more rapidly than
optically active selenoxides.14 Therefore, substituents,
bulkier than in the case of the selenoxides or some other
stabilizing method, such as intramolecular coordination
of amino group, will be necessary to isolate an optically
active telluroxide.
P r ep a r a tion of Ra cem ic Tellu r oxid es 1a -d a n d
2a -c. 2,4,6-Triisopropylphenyl mesityl telluride (3a ) was
synthesized in 77% yield by reacting mesitylmagnesium
bromide and bis(2,4,6-triisopropylphenyl)ditelluride
(Scheme 1). Similarly, 2,4,6-tri-tert-butyldiphenyl tel-
luride (3b) and 2,4,6-tri-tert-butylphenyl mesityl telluride
(3c) were synthesized in yields of 90 and 88% by reacting
2,4,6-tri-tert-butylphenyllithium with diphenyl ditelluride
or dimesityl ditelluride, respectively. Telluride 3d pos-
sessing a 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt)
group, which is known to be extremely bulky,15,16 was
synthesized in 62% yield by reacting 2,4,6-tris[bis(tri-
methylsilyl)methyl]phenyllithium16 with diphenyl ditel-
luride. 2-(N,N-Dimethylaminomethyl)phenyl mesityl tel-
luride (4a ) and 2-[(N,N-dimethylamino)methyl]-2′,4′,6′-
triisopropyldiphenyl telluride (4b) were synthesized in
yields of 54 and 90% by reacting 2-(N,N-dimethylamino-
methyl)phenyllithium with dimesityl ditelluride or
bis(2,4,6-triisopropylphenyl) ditelluride, respectively.
2-[(N,N-Dimethylamino)methyl]-2′,4′,6′-tri-tert-butyldi-
phenyl telluride (4c) was synthesized in 64% yield by
reacting 2,4,6-tri-tert-butylphenyllithium with bis[2-(N,N-
dimethylaminomethyl)phenyl] ditelluride. Finally, asym-
metric diaryl telluroxides 1a -d possessing a bulky group
and 2a -c possessing an intramolecular amino group
were obtained in yields of 72-99% by oxidation of the
corresponding tellurides 3a -d and 4a -c with tert-butyl
hypochlorite.
Reagents and conditions: (a) Mg, THF, rt; (b) (TipTe)2; (c)
n-BuLi, THF, -60 °C; (d) (PhTe)2; (e) (MesTe)2; (f) (DMAMPTe)2;
(g) t-BuOCl, MeOH, CH2Cl2, -25 °C, then aq NaOH; Tip: 2,4,6-
triisopropylphenyl; DMAMP: 2-{(N,N-dimethylamino)methyl}-
phenyl.
F igu r e 1. Chromatographic resolution of racemic diaryl
telluroxides 1a -c by means of HPLC using an optically active
column (Daicel Chiralpak AS).
Op tica l Resolu tion of Tellu r oxid es by Mea n s of
HP LC. Diaryl telluroxide (1a ) was subjected to several
columns with a chiral stationary phase using HPLC at
an analytical scale. Racemic telluroxide 1a was resolved
into two peaks corresponding to the enantiomers when
optically active columns, such as Daicel Chiralpak AS
and AD, and Chiralcel OB, OJ , OC, OD, OF, and OJ ,
were used. Among these columns, the chromatogram of
telluroxide 1a using a column with amylose carbamate
derivative/silica gel (Daicel Chiralpak AS) as a chiral
stationary phase showed the best resolution on an
analytical scale (eluent: hexane/isopropyl alcohol ) 95/
5) (Figure 1). Similarly, telluroxides 1b (eluent: hexane/
isopropyl alcohol ) 95/5) and 1c (eluent: hexane/
isopropyl alcohol ) 98/2) could also be resolved into their
enantiomers. On the other hand, when telluroxide 1d was
subjected to several optically active columns at an
analytical scale, optical resolution was not achieved,
maybe because the very bulky Tbt group inhibited
recognition of the asymmetry of the telluroxide moiety
on the chiral stationary phase.
(14) (a) Detty, M. R. J . Org. Chem. 1980, 45, 274. (b) Shimizu, T.;
Kobayashi, M.; Kamigata, N. Bull. Chem. Soc. J pn. 1988, 61, 3761.
(15) For review, see: (a) Tokitoh, N.; Matsuhashi, Y.; Shibata, K.;
Matsumoto, T.; Suzuki, H.; Saito, M.; Manmaru, K.; Okazaki, R. Main
Group Met. Chem. 1994, 17, 55. (b) Tokitoh, N.; Okazaki, R. Main
Group Chem. News 1995, 3 (3), 4. (c) Tokitoh, N. J . Synth. Org. Chem.
J pn. 1996, 52, 136; see also references therein.
(16) Okazaki, R.; Unno, M.; Inamoto, N. Chem. Lett. 1987, 2293.

Enantiomerically Pure Telluroxides
optically
J . Org. Chem., Vol. 65, No. 7, 2000 2129
Ta ble 1. Ch r om a togr a p h ic Resolu tion of Tellu r oxid es
first enantiomer
[R]D (CHCl3)c
second enantiomer
telluroxides
active columna
i-PrOH,b %
ee (%)d
[R]D (CHCl3)
ee (%)
1c
2b
2c
AS
OD
OD
2
30
5
+25.3 (c 0.22)
+39.5 (c 0.15)
+166.2 (c 0.32)
100
100
100
-23.6 (c 0.11)
-11.9 (c 0.13)
-66.1 (c 0.12)
93
38
40
a
b
AS: Daicel Chiralpak AS, AD: Daicel Chiralcel OD. The volume percentage of isopropyl alcohol in hexane used as mobile phase.
c Specific rotations were taken at 25-27 °C. Enantiomeric purities were determined by HPLC analysis.
d
F igu r e 2. Chromatographic resolution of racemic diaryl
telluroxides 2a -c by means of HPLC using an optically active
column (Daicel Chiralcel OD).
F igu r e 3. Chromatographic resolution of racemic diaryl
telluroxides 2a and 2b by means of HPLC at -3 °C (Daicel
Chiralcel OD).
F igu r e 4. CD spectra of optically active telluroxides (+)-1b,
(-)-1b, (+)-1c, and (-)-1c and selenoxides (R)-(+)-5 and (S)-
(-)-5 in acetonitrile.
Chromatographic resolution of diaryl telluroxide 2a
possessing an intramolecular amino group was also
examined using several chiral stationary phases at an
analytical scale. Racemic telluroxide 2a was resolved into
two peaks corresponding to the enantiomers when a
column with cellulose carbamate derivative/silica gel
(Daicel Chiralcel OD, eluent: hexane/isopropyl alcohol
) 60/40) was employed, as shown in Figure 2. Similarly,
telluroxides 2b (eluent: hexane/isopropyl alcohol ) 70/
30) and 2c (eluent: hexane/isopropyl alcohol ) 95/5)
could also be resolved into their enantiomers.
The chromatograms of telluroxides 1a , 2a , and 2b
showed an unusual shape and indicated that racemiza-
tion had occurred in the column, while the racemization
of telluroxides 1b, 1c, and 2c was not observed in the
column. However, when chromatographic resolution was
carried out at -3 °C, telluroxides 2a and 2b could be
optically resolved very nicely into two peaks correspond-
ing to the enantiomers without racemization in the
column, as shown in Figure 3. These results show that
bulky substituents effectively inhibited the racemization
of telluroxides in the column.
enantiomeric purities were determined by HPLC analy-
sis. Our inability to isolate optically pure telluroxide (-)-
1c is due to tailing of the first eluted enantiomer.
Similarly, optically pure telluroxides (+)-2b and (+)-2c
were isolated from the first eluent, and optically active
telluroxides (-)-2b and (-)-2c were obtained from the
second eluent. The results are summarized in Table 1.
Optically active telluroxides 1a , 1b, and 2a could not be
isolated because racemization of these telluroxides oc-
curred during concentration of the solution, and the CD
spectra of optically active telluroxides (+)- and (-)-1b
could be narrowly measured.
Cir cu la r Dich r oism Sp ectr a a n d Absolu te Con -
figu r a tion of Op tica lly Active Tellu r oxid es. The CD
spectra of optically active telluroxides (+)-1b and (+)-1c
showed positive first Cotton effects at 313 and 305 nm,
respectively, while those of (-)-1b and (-)-1c showed
negative effects in the same region, as shown in Figure
4. These first Cotton effects correspond well with those
of optically active 2,4,6-tri-tert-butyldiphenyl selenoxides
{(R)-(+)-5 and (S)-(-)-5}, for which the relationship
The optical resolution of racemic telluroxides 1a -c and
2a -c was carried out by HPLC using the same type of
optically active column at a preparative scale. For tel-
luroxide 1c, repeated resolution of the first and second
fractions gave optically active telluroxides. The first
eluted enantiomer had a positive specific rotation {(+)-
1c: ee 100%; [R]D +25.3 (c 0.22, CHCl3)}, and the second
eluted enantiomer had a negative specific rotation
{(-)-1c: ee 93%; [R]D -23.6 (c 0.11, CHCl3)}, and their
between the absolute configurations and the CD spectra
has been clarified.14b Therefore, the absolute configura-

2130 J . Org. Chem., Vol. 65, No. 7, 2000
Taka et al.
Ta ble 2. F ir st Or d er Ra te Con sta n ts for Ra cem iza tion of Op tica lly Active Tellu r oxid es in Solu tion sa
k/s-1 (t1/2/h)
solvent
CHCl3
(R)-(+)-1b
(R)-(+)-1c
(R)-(+)-2b
(R)-(+)-2c
(S)-(-)-7b
(R)-(+)-8c
7.41 × 10-4 (0.260) 2.75 × 10-6 (69.3) 1.36 × 10-4 (1.41) 1.45 × 10-7 (1327)
Ae
A
MeOH
Bf
B
6.05 × 10-5 (3.18)
B
B
2.00 × 10-4 (0.963) 5.58 × 10-6 (34.5) 6.00 × 10-6 (32.1)
MeOH/H2Od
B
1.18 × 10-3 (0.163) 5.13 × 10-5 (3.76) 3.34 × 10-5 (5.76)
a
b
d
In ca. 5 mM solution at 26 ( 1 °C. Reference 11. c Reference 14b. MeOH/H2O ) 4/1. e A: No racemization was observed even after
5 days. f B: Racemization was completed within 1 min.
F igu r e 6. Correlation between enantiomeric purity and 18O-
labeled telluroxide for racemization of optically active tellurox-
ides (R)-(+)-1c and 2c in methanol in the presence of H218O.
and 2c showed a good linear relationship with first-order
rate plots, and the rate constants are summarized in
Table 2. The rate constants of telluroxides (R)-(+)-1b and
-1c in chloroform were 7.41 × 10-4 and 2.75 × 10-6 s-1
,
respectively. The racemization of optically active tel-
luroxides (R)-(+)-2b and -2c was also observed, and the
rate constants in chloroform were 1.36 × 10-4 and 1.45
× 10-7 s-1, respectively. These results mean that tel-
luroxides 1c and 2c are more stable than telluroxides
1b and 2b, respectively, against racemization in chloro-
form, and a bulky group on the tellurium atom was
effective for preventing the racemization of telluroxide.
On the other hand, (S)-(-)-2-(N,N-dimethylaminometh-
yl)diphenyl selenoxides{(S)-(-)-7}11 and (R)-(+)-mesityl
phenyl selenoxide {(R)-(+)-8}14b did not racemize even
after 5 days in chloroform at room temperature. These
results show that telluroxides racemize more easily than
selenoxides in chloroform.
F igu r e 5. CD spectra of optically active telluroxides (+)-2b,
(-)-2b, (+)-2c, and (-)-2c and sulfoxide (S)-(-)-6 in cyclohex-
ane.
tion of telluroxides (+)-1b and (+)-1c is determined to
be R and that of (-)-1b and (-)-1c is S.
The CD spectra of optically active telluroxides (+)-2b
and (+)-2c also showed positive first Cotton effects at 308
and 317 nm, respectively, and those of (-)-2b and (-)-
2c showed negative effects in the same region, as shown
in Figure 5. The absolute configuration of optically active
telluroxides (-)-2b and (-)-2c was determined by com-
paring the first Cotton effects of their CD spectra with
those of (S)-(-)-2-(N,N-dimethylaminomethyl)-4′-meth-
yldiphenyl sulfoxide{(S)-(-)-6}.11,17 Consequently, the
absolute configuration of telluroxides (-)-2b and (-)-2c
is determined to be S, and that of (+)-2b and (+)-2c is
R.
The racemization of telluroxides (R)-(+)-1b, 1c, 2b, and
2c proceeded faster in methanol than in chloroform. The
addition of water to the methanol solution of (R)-(+)-1c
and -2c accelerated their racemization. These results
indicate that the racemization of telluroxide occurs due
to a trace amount of water which remains in the solvent,
despite careful purification of the solvent. Thus, a mech-
anism via an achiral hydrate formed by the addition of
water to telluroxide for racemization is proposed. To
confirm this mechanism involving an achiral tetracoor-
dinated hydrate, the oxygen exchange reaction of tel-
luroxide was investigated using H218O. To a methanol
solution of (R)-(+)-1c (ee 89%) was added H218O (97 atom
Con figu r a tion a l Sta bility of Op tica lly Active Tel-
lu r oxid es. The kinetics for the racemization of optically
active telluroxides was examined. The rates of racem-
ization for optically active telluroxides (R)-(+)-1b, 1c, 2b,
%
18O excess; 30 equiv), and the mixture was stirred at
room temperature. The mass spectrum (FAB) showed 41
and 72% 18O-enriched telluroxide at ee values of 34 and
12%, respectively, as shown in Figure 6. Similarly, the
mass spectrum (FAB) of (R)-(+)-2c (ee 47%), showed 25,
47, and 60% 18O-enriched telluroxide at ee values of 30,
20, and 8%, respectively.
(17) (S)-(-)-2-(N,N-Dimethylaminomethyl)-4′-methyldiphenyl sul-
foxide{(S)-(-)-6} was prepared by reacting (S)S-(-)-menthyl-(-)-4-
methylphenyl sulfinate and 2-(N,N-dimethylaminomethyl)phenyl-
magnesium bromide according to the Andersen’s method: Andersen,
K. K.; Gaffield, W.; Papanikolaou, N. E.; Foley, J . W.; Perkins, R. I. J .
Am. Chem. Soc. 1964, 86, 5637.

Enantiomerically Pure Telluroxides
J . Org. Chem., Vol. 65, No. 7, 2000 2131
Telluroxides (R)-(+)-2b and -2c with an intramolecular
amino group were more stable against the racemization
than the kinetically stabilized telluroxide (R)-(+)-1b.
These results suggest that telluroxide is stabilized by the
coordination of an intramolecular amino group to the
tellurium atom. To obtain further experimental evidence
for such intramolecular coordination, variable tempera-
1
ture H NMR measurements were performed. As shown
in Figure 7, methyl protons of the amino group of
telluroxide rac-2b were observed as a singlet signal in
chloroform-d at 298 K, however, two signals correspond-
ing to the two methyl groups on the amino moiety of
telluroxide were observed at 223 K (νab ) 108.4 Hz).
These results suggest the tellurium and nitrogen atoms
interact, and the two methyl groups are nonequivalent
at low temperature. The coalescence temperature was
258 K, and the exchange energy of the two methyl groups
of telluroxide rac-2b was calculated to be 12.2 kcal mol-1
.
Similarly, the energy of rac-2c was calculated to be 11.6
kcal mol-1 (νab ) 259.7 Hz at 223 K; coalescence temper-
ature ) 258 K). These values include the coordination
energy of the amino group to the tellurium atom and the
rotation energy of the CH2-N bond or the inversion
energy on the nitrogen atom. The rotation energy of the
CH2-N bond (6.7 kcal mol-1) and the inversion energy
on the nitrogen atom (3.8 kcal mol-1) for N-cyclohexyl-
N-methylbenzylamine have been calculated by Iwaoka
and Tomoda.18 Therefore, the experimental values for rac-
F igu r e 7. 1H NMR signals of methyl protons of amino group
of variable temperature NMR spectra for racemic telluroxides
rac-2b and 2c in CDCl3.
optically active telluroxides underwent racemization
faster than selenoxides in solution. The stabilization
energies of telluroxides 2b and 2c by intramolecular
coordination of the amino group to the tellurium atom
were estimated to be ca. 5 kcal mol-1 on the basis of
1
variable temperature H NMR measurements.
1
2b and -2c determined by H NMR measurements were
taken to be the sum of the coordination energy of the
amino group to the tellurium atom and the rotation
energy of the CH2-N bond. Thus, the coordination energy
for telluroxides rac-2b and -2c was estimated to be 5.5
and 4.9 kcal mol-1, respectively. These estimated energies
of telluroxides 2b and 2c are not so large that we have
initially expected. Thus, we consider the reason why the
optically active telluroxides 2b and 2c were stable
against racemization despite the coordination energy
values seemed to be insufficient as follows: the N,N-
dimethylaminomethyl group is preventing the racemiza-
tion not only by intramolecular coordination of the amino
moiety to the tellurium atom (thermodynamic stabiliza-
tion) but also steric protection by the bulkiness of the
substituent in itself (kinetic stabilization).
Exp er im en ta l Section
Gen er a l. Tetrahydrofuran (THF) was distilled from sodium
benzophenone ketyl before use. Acetonitrile, cyclohexane,
dichloromethane, hexane, and isopropyl alcohol were distilled
from calcium hydride before use. Methanol was distilled from
magnesium cake and stored with 3 A molecular sieves under
nitrogen. TLC were performed with Merck Art. 5554 DC-
Alufolien Kieselgel 60 F254. Column chromatography was
performed with Merck 7734 Kieselgel 60.
Ma ter ia ls. 2-(N,N-Dimethylaminomethyl)bromobenzene11,19
and 2,4,6-tris[bis(trimethylsilyl)methyl]bromobenzene16 were
prepared according to the procedure in the literature.
Gen er a l P r oced u r e for P r ep a r a tion of Dia r yl Tel-
lu r id e 3a -d : 2,4,6-Tr iisop r op ylp h en yl Mesityl Tellu r id e
(3a ). To the Grignard reagent prepared from mesityl bromide
(4.01 g, 20.0 mmol) and magnesium (0.49 g, 20.0 mmol) in
anhydrous THF (60 mL) was slowly added an anhydrous THF
solution (30 mL) of bis(triisopropylphenyl)ditelluride (11.55 g,
20.0 mmol) under nitrogen. The solution was stirred for an
additional 2 h and was allowed to stand until room temper-
ature. Saturated brine was added to the solution, and the
organic layer was separated. The organic component remain-
ing in the aqueous layer was extracted with ether, and the
combined organic layer was washed with water and dried over
anhydrous magnesium sulfate. The solution was concentrated
under reduced pressure, and purification by silica gel column
chromatography (eluent, pentane) gave telluride 3a (6.89 g,
77%): oil; IR (KBr) 2975, 1450, 1360, 870, 840 cm-1; 1H NMR
(500 MHz, CDCl3) δ 1.02 (12H, d, J ) 6.3 Hz), 1.23 (6H, d, J
) 6.8 Hz), 2.23 (3H, s), 2.36 (6H, s), 2.85 (1H, hep, J ) 6.8
Con clu sion
We succeeded in isolating kinetically and thermody-
namically stabilized optically pure telluroxides by HPLC
using optically active columns. The absolute configura-
tions of optically active telluroxides were determined by
comparing the signs of their specific rotations and CD
spectra with those of sulfur and selenium analogues, and
optically active telluroxides (-)-1 and -2 were determined
to be S. The results of kinetic studies indicated that a
bulky group on the tellurium atom and intramolecular
coordination by the amino group to the tellurium atom
were very effective at preventing racemization, although
(19) (a) Yoshifuji, M.; Kamijo, K.; Toyota, K. Bull. Chem. Soc. J pn.
1993, 66, 3440. (b) Yoshifuji, M.; Kamijo, K.; Toyota, K. Tetrahedron
Lett. 1994, 35, 3971.
(18) Iwaoka, M.; Tomoda, S. J . Am. Chem. Soc. 1996, 118, 8077.

2132 J . Org. Chem., Vol. 65, No. 7, 2000
Taka et al.
Hz), 3.59 (2H, hep, J ) 6.3 Hz), 6.84 (2H, s), 6.94 (2H, s); 13C
NMR (125 MHz, CDCl3) δ 20.8, 24.0, 24.4, 28.2, 33.9, 39.4,
120.2, 120.8, 121.5, 127.7, 137.8, 144.0, 149.3, 154.1; mass (EI)
m/z 452 (130Te, M+), 450 (128Te, M+), 333, 249, 203, 119.
2,4,6-Tr i-ter t-bu tyld ip h en yl Tellu r id e (3b). Yield 90%;
mp 127-128 °C; IR (KBr) 2975, 1580, 1460, 1130, 875, 740
cm-1; 1H NMR (500 MHz, CDCl3) δ 1.35 (9H, s), 1.58 (18H, s),
6.56 (2H, m), 6.97 (3H, m), 7.52 (2H, s); 13C NMR (125 MHz,
CDCl3) δ 31.4, 33.1, 35.1, 40.1, 109.0, 122.5, 125.4, 125.7, 129.0,
131.4, 151.1, 157.1; MS (EI) m/z 452 (130Te, M+), 450 (128Te,
M+), 375, 245, 77.
1583, 1456, 1340, 847, 751 cm-1; H NMR (500 MHz, CDCl3)
δ 1.35 (9H, s), 1.56 (18H, s), 2.24 (6H, s), 3.44 (2H, s), 5.60
(1H, d, J ) 7.5 Hz), 6.65 (1H, dd, J ) 7.5 Hz), 6.89 (1H, dd, J
) 7.5 Hz), 6.97 (1H, d, J ) 7.5 Hz), 7.45 (2H, s); 13C NMR
(125 MHz, CDCl3) δ 31.4, 31.6, 33.2, 40.0, 43.9, 66.4, 117.5,
121.7, 124.5, 127.2, 128.1, 131.0, 132.9, 139.5, 149.9, 157.0;
MS (EI) m/z 509 (130Te, M+), 507 (128Te, M+), 264, 134, 91, 57.
Gen er a l P r oced u r e for th e Oxid a tion of Tellu r id e
Usin g ter t-Bu tyl Hyp och lor ite: 2,4,6-Tr iisop r op ylp h en yl
Mesityl Tellu r oxid e (r a c-1a ). To a dichloromethane solution
(20 mL) containing telluride 3a (0.90 g, 2.0 mmol) and
methanol (20 mL) was slowly added a dichloromethane solu-
tion (10 mL) of tert-butyl hypochlorite (0.22 g, 2.0 mmol) at
-25 °C under nitrogen, and the solution was stirred for an
additional 30 min and was allowed to stand until room
temperature. After aq sodium hydroxide (0.40 g in 20 mL) was
poured into the reaction mixture, the organic layer was
separated. The organic component remaining in the aqueous
layer was extracted with dichloromethane, and the combined
organic layer was dried over anhydrous sodium sulfate. The
solution was concentrated under reduced pressure, and puri-
fication by silica gel column chromatography (eluent, dichlo-
romethane/methanol ) 100/6) gave telluroxide rac-1a (0.81 g,
86%): mp 165-167 °C; IR (KBr) 2960, 1590, 1560, 1460, 1360,
1
2,4,6-Tr i-ter t-bu tylp h en yl Mesityl Tellu r id e (3c). Yield
88%; pale yellow viscous oil; IR (KBr) 2975, 1590, 1455, 1120,
840 cm-1; 1H NMR (500 MHz, CDCl3) δ 1.30 (9H, s), 1.47 (18H,
s), 1.83 (6H, s), 2.17 (3H, s), 6.70 (2H, s), 7.33 (2H, s); 13C NMR
(125 MHz, CDCl3) δ 20.6, 25.2, 31.3, 31.6, 33.1, 39.8, 110.8,
119.4, 122.2, 128.7, 136.3, 141.7, 149.9, 156.5; MS (EI) m/z 494
(
130Te, M+), 492 (128Te, M+), 250, 119.
2,4,6-Tr is[b is(t r im et h ylsilyl)m et h yl]d ip h en yl Tellu -
r id e (3d ). Yield 62%; mp 141.2-141.9 °C; IR (KBr) 2956, 1400,
1246, 690 cm-1; 1H NMR (500 MHz, CDCl3) δ -0.03 (36H, s),
0.05 (18H, s), 1.33 (1H, s), 2.98 (1H, brs), 3.03 (1H, brs), 6.42
(1H, brs), 6.55 (1H, brs), 7.10-7.22 (3H, m), 7.57-7.62 (2H,
m); 13C NMR (125 MHz, CDCl3) δ 0.6, 0.7, 30.3, 35.7, 117.0,
120.4, 123.7, 125.2, 127.2, 129.3, 137.3, 144.4; MS (EI, 70 eV)
m/z 758 (130Te, M+), 756 (128Te, M+), 680, 552, 135, 73.
840, 740 cm-1; H NMR (500 MHz, CDCl3) δ 1.07 (6H, d, J )
1
6.8 Hz), 1.15 (6H, d, J ) 6.8 Hz), 1.22 (6H, d, J ) 6.8 Hz),
2.25 (3H, s), 2.53 (6H, s), 2.85 (1H, hep, J ) 6.8 Hz), 3.75 (2H,
hep, J ) 6.8 Hz), 6.83 (2H, s), 7.03 (2H, s); 13C NMR (125 MHz,
CDCl3) δ 20.9, 21.2, 23.8, 24.4, 24.7, 32.7, 34.1, 123.3, 130.5,
131.3, 131.7, 140.6, 142.3, 152.2, 153.6; MS (EI) m/z 468 (130Te,
M+), 466 (128Te, M+), 452, 333, 249, 203, 119. Anal. Calcd for
Gen er a l P r oced u r e for P r ep a r a tion of Dia r yl Tel-
lu r id e 4a a n d 4b: 2-(N,N-Dim eth yla m in om eth yl)p h en yl
Mesityl Tellu r id e (4a ). To the lithium reagent prepared from
2-(N,N-dimethylaminomethyl)bromobenzene (1.07 g, 5.0 mmol)
and n-BuLi (1.5 mol mL-1 in hexane; 4.1 mL, 6.0 mmol) in
anhydrous THF (50 mL) was slowly added an anhydrous THF
solution (50 mL) of dimesityl ditelluride (2.47 g, 5.0 mmol)
under nitrogen at -60 °C. The solution was stirred for an
additional 2 h and was allowed to stand until room temper-
ature. Saturated brine was added to the solution, and the
organic layer was separated. The organic component remain-
ing in the aqueous layer was extracted with ether, and the
combined organic layer was washed with water and dried over
anhydrous magnesium sulfate. The solution was concentrated
under reduced pressure, and purification by silica gel column
chromatography (eluent, hexane/ether ) 2/1) gave telluride
4a (1.02 g, 54%): pale yellow oil; IR (KBr) 2828, 1458, 1027,
846, 746 cm-1; 1H NMR (500 MHz, CDCl3) δ 2.26 (6H, s), 2.30
(3H, s), 2.50 (6H, s), 3.50 (2H, s), 6.84 (1H, t, J ) 7.4 Hz), 6.93
(1H, d, J ) 7.6 Hz), 6.97 (2H, s), 7.01-7.08 (2H, m); 13C NMR
(125 MHz, CDCl3) δ 21.1, 29.0, 43.9, 66.6, 122.8, 123.5, 125.5,
127.2, 127.8, 128.7, 133.6, 138.4, 141.0, 145.5; MS (EI) m/z 383
C
24H34OTe: C, 61.84; H, 7.35. Found: C, 61.55; H, 7.65.
2,4,6-Tr i-ter t-bu tyld ip h en yl Tellu r oxid e (r a c-1b). Yield
84%; mp 122-124 °C; IR (KBr) 2960, 1580, 1480, 1120, 880,
750 cm-1; 1H NMR (500 MHz, CDCl3) δ 1.35 (9H, s), 1.48 (18H,
s), 6.94-6.96 (2H, m), 7.22-7.29 (3H, m), 7.51 (2H, s); 13C
NMR (125 MHz, CDCl3) δ 31.1, 33.7, 35.1, 38.8, 124.0, 129.1,
130.1, 130.5, 133.7, 141.2, 152.7, 157.0; MS (EI) m/z 468 (130Te,
M+), 466 (130Te, M+), 452, 375, 245, 77; UV (MeCN) λmax 300.0
(ꢀ 1.14 × 103) nm, 244.0 (ꢀ 5.51 × 103), 215.0 (ꢀ 1.01 × 104)
nm. Anal. Calcd for C24H34OTe C, 61.84; H, 7.35. Found: C,
62.05; H, 7.81.
2,4,6-Tr i-ter t-bu tylp h en yl Mesityl Tellu r oxid e (r a c-1c).
Yield 97%; mp 121-122 °C; IR (KBr) 2960, 1600, 1460, 800
cm-1; 1H NMR (500 MHz, CDCl3) δ 1.31 (9H, s), 1.34 (18H, s),
2.05 (6H, brs), 2.21 (3H, s), 6.75 (2H, s), 7.29 (2H, s); 13C NMR
(125 MHz, CDCl3) δ 20.9, 31.1, 31.5, 33.0, 34.4, 39.3, 124.5,
130.1, 133.0, 138.3, 140.7, 142.2, 151.1, 157.4; FAB-MS (3-
(
130Te, M+), 381 (128Te, M+), 263, 220, 134, 119, 91, 58.
nitrobenzyl alcohol) m/z 511 (130Te, M+ + 1), 509 (130Te, M+
+
2-(N,N-Dim et h yla m in om et h yl)-2′,4′,6′-t r iisop r op yld i-
1), 391, 119; UV (MeOH) λmax 236.0 (ꢀ 1.77 × 104) nm; UV
(MeCN) λmax 243.0 (ꢀ 2.80 × 104), 211.0 (ꢀ 4.97 × 104) nm. Anal.
Calcd for C27H40OTe: C, 63.81; H, 7.93. Found: C, 63.56; H
8.15.
p h en yl Tellu r id e (4b). Yield 90%; mp 108-109 °C; IR (KBr)
1
2969, 1458, 1032, 848, 742 cm-1; H NMR (500 MHz, CDCl3)
δ 1.14 (12H, d, J ) 7.0 Hz), 1.29 (6H, d, J ) 7.0 Hz), 2.26 (6H,
s), 2.92 (1H, hep, J ) 7.0 Hz), 3.52 (2H, s), 3.76 (2H, hep, J )
7.0 Hz), 6.80-7.00 (4H, m), 7.07 (2H, s); 13C NMR (125 MHz,
CDCl3) δ 22.7, 24.0, 24.7, 31.6, 34.2, 39.2, 44.0, 66.7, 121.0,
123.9, 125.0, 125.3, 127.6, 128.5, 134.5, 140.7, 149.8, 155.1;
MS (EI) m/z 468 (130Te, M+ + 1), 466 (128Te, M+ + 1), 424, 377,
291, 264, 220, 135, 91.
2-(N,N-Dim et h yla m in om et h yl)-2′,4′,6′-t r i-ter t-b u t yl-
d ip h en yl Tellu r id e (4c). To the lithium reagent prepared
from 2,4,6-tri-tert-butylbromobenzene (13.00 g, 40.0 mmol) and
n-BuLi (1.54 mol mL-1 in hexane; 28.6 mL, 44.0 mmol) in
anhydrous THF (200 mL) was slowly added an anhydrous THF
solution (100 mL) of bis[2-(N,N-dimethylaminomethyl)phenyl]
ditelluride (20.94 g, 40.0 mmol) under nitrogen at -60 °C. The
solution was stirred for an additional 2 h and was allowed to
stand until room temperature. Saturated brine was added to
the solution, and the organic layer was separated. The organic
component remaining in the aqueous layer was extracted with
ether, and combined organic layer was washed with water and
dried over anhydrous magnesium sulfate. The solution was
concentrated under reduced pressure, and purification by silica
gel column chromatography (eluent, hexane/ether ) 2/1) gave
telluride 4c (12.98 g, 64%): mp 139-140 °C; IR (KBr) 2948,
2,4,6-Tr is[bis(tr im eth ylsilyl)m eth yl]diph en yl Tellu r ox-
id e (r a c-1d ). Yield 74%; mp 172-174 °C; IR (KBr) 2950, 1400,
1250, 840, 690 cm-1; 1H NMR (500 MHz, CDCl3) δ -0.10 (9H,
s), -0.07 (9H, s), 0.039 (9H, s), 0.043 (9H, s), 0.11 (9H, s), 0.12
(9H, s), 1.35 (1H, s), 2.67 (1H, brs), 2.74 (1H, brs), 6.32 (1H,
brs), 6.43 (1H, brs), 7.40-7.50 (3H, m), 7.78-7.82 (2H, m); 13
C
NMR (125 MHz, CDCl3) δ 0.4, 0.6, 0.7, 0.9, 1.1, 26.9, 27.0, 30.9,
123.4, 128.0, 128.2, 129.7, 130.8, 131.1, 135.1, 147.4, 151.0,
151.4; FAB-MS (3-nitrobenzyl alcohol) m/z 775 (130Te, M+
+
1), 773 (128Te, M+ + H). Anal. Calcd for C33H64OSi6Te: C, 51.28;
H, 8.35. Found: C, 51.49; H, 8.52.
2-(N,N-Dim eth ylam in om eth yl)ph en yl Mesityl Tellu r ox-
id e (r a c-2a ). Yield 72%; mp 188-189 °C; IR (KBr) 2820, 1439,
1022, 756, 713 cm-1; H NMR (500 MHz, CDCl3) δ 2.08 (6H,
1
s), 2.25 (3H, s), 2.38 (6H, s),3.29 (1H, d, J ) 13.8 Hz), 3.35
(1H, d, J ) 13.8 Hz), 6.82 (2H, s), 7.18 (1H, d, J ) 7.3 Hz),
7.40 (1H, dd, J ) 7.3 Hz), 7.48 (1H, dd, J ) 7.3 Hz), 8.33 (1H,
d, J ) 7.3 Hz); 13C NMR (125 MHz, CDCl3) δ 20.8, 22.4, 44.3,
63.2, 128.0, 128.4, 129.4, 130.3, 131.7, 133.48, 133.50, 140.4,
140.5, 142.5; MS (EI) m/z 399 (130Te, M+), 397 (128Te, M+), 253,
207, 134, 119, 91, 77; UV (cyclohexane) λmax 309.7 (sh, ꢀ 2.48
× 103), 269.0 (sh, ꢀ 7.92 × 103), 231.8 (sh, ꢀ 3.85 × 104), 207.4

Enantiomerically Pure Telluroxides
J . Org. Chem., Vol. 65, No. 7, 2000 2133
(ꢀ 8.59 × 104) nm. Anal. Calcd for C18H23NOTe: C, 54.46; H,
5.84; N, 3.53. Found: C, 54.14; H, 5.92; N, 3.66.
nm. Anal. Calcd for C27H40OTe: C, 63.81; H, 7.93. Found: C,
63.83; H, 8.41. 1H NMR, 13C NMR, IR, UV, and MS spectra
were almost same with those of racemic one.
2-(N,N-Dim et h yla m in om et h yl)-2′,4′,6′-t r iisop r op yld i-
p h en yl Tellu r oxid e (r a c-2b). Yield 99%; mp 211-212 °C;
IR (KBr) 2963, 1458, 1384, 1101, 741 cm-1; 1H NMR (500 MHz,
CDCl3) δ 1.00 (6H, d, J ) 7.0 Hz), 1.24 (6H, d, J ) 7.0 Hz),
1.25 (6H, d, J ) 7.0 Hz), 2.21 (6H, s), 2.88 (1H, hep, J ) 7.0
Hz), 3.31 (1H, d, J ) 13.8 Hz), 3.59 (2H, hep, J ) 7.0 Hz),
3.79 (1H, d, J ) 13.8 Hz), 7.04 (2H, s), 7.12-7.20 (1H, m),
7.34-7.38 (2H, m), 7.86-7.90 (1H, m); 13C NMR (125 MHz,
CDCl3) δ 23.67, 23.73, 24.5, 24.7, 32.5, 34.1, 44.3, 62.9, 122.4,
128.3, 128.6, 130.3, 132.1, 134.90, 134.93, 141.1, 151.6, 154.0;
MS (EI) m/z 483 (130Te, M+), 481 (128Te, M+), 465, 438, 336,
291, 264, 175, 134, 91; UV (cyclohexane) λmax 310 (sh, ꢀ 2.48 ×
103), 269 (sh, ꢀ 7.92 × 103), 232 (sh, ꢀ 3.85 × 104), 207 (ꢀ 8.59
× 104) nm. Anal. Calcd for C24H35NOTe: C, 59.91; H, 7.33; N,
2.91. Found: C, 59.46; H, 7.31; N, 3.13.
Com p ou n d (S)-(-)-1c. 93% ee; mp 114-115 °C; [R]D -23.6
(c 0.11, CHCl3), [R]D -21.3 (c 0.38, MeCN), [R]435 -118.2 (c
0.11, CHCl3), [R]435 -54.4 (c 0.38, MeCN); CD (MeCN) 313 ([θ]
-1.6 × 104), 286 ([θ] +1.4 × 104), 264 ([θ] -1.8 × 104), 246
([θ] +2.9 × 104), 236 (sh, [θ] +1.9 × 104), 212 ([θ] +1.1 × 105)
nm. Anal. Calcd for C27H40OTe: C, 63.81; H, 7.93. Found: C,
64.18; H, 8.24. 1H NMR, 13C NMR, IR, UV, and MS spectra
were almost same with those of racemic one.
Com p ou n d (R)-(+)-2b. 100% ee; mp 189-191 °C; [R]D
+39.5 (c 0.15, CHCl3), [R]435 +142.9 (c 0.15, CHCl3); CD
(cyclohexane) 308 ([θ] +2.50 × 104), 235 ([θ] -5.31 × 104) nm.
Anal. Calcd for C24H35NOTe: C, 59.91; H, 7.33; N, 2.91.
Found: C, 59.59; H, 7.13; N, 2.81. 1H NMR, 13C NMR, IR, UV,
and MS spectra were almost same with those of racemic one.
Com p ou n d (S)-(-)-2b. 38% ee; mp 178-182 °C; [R]D
-11.9 (c 0.13, CHCl3), [R]435 -58.5 (c 0.13, CHCl3); CD
(cyclohexane) 307 ([θ] -1.86 × 104), 236 ([θ] +3.69 × 104) nm.
Anal. Calcd for C24H35NOTe: C, 59.91; H, 7.33; N, 2.91.
Found: C, 59.52; H, 7.40; N, 3.16. 1H NMR, 13C NMR, IR, UV,
and MS spectra were almost same with those of racemic one.
Com p ou n d (R)-(+)-2c. 100% ee; mp 140-141 °C; [R]D
+166.2 (c 0.32, CHCl3), [R]435 +477.9 (c 0.32, CHCl3); CD
(cyclohexane) 317 ([θ] +1.15 × 105), 272 ([θ] -7.71 × 104), 245
([θ] +1.63 × 105), 229 ([θ] -6.46 × 104), 219 ([θ] +1.96 × 104),
204 ([θ] -3.15 × 105) nm. Anal. Calcd for C27H41NOTe: C,
2-(N,N-Dim et h yla m in om et h yl)-2′,4′,6′-t r i-ter t-b u t yl-
d ip h en yl Tellu r oxid e (r a c-2c). Yield 97%; mp 143-145 °C;
IR (KBr) 2963, 1597, 1460, 1362, 847, 764 cm-1; 1H NMR (500
MHz, CDCl3) δ 1.37 (9H, s), 1.49 (18H, brs), 2.36 (6H, brs),
3.16 (1H, d, J ) 13.0 Hz), 4.44 (1H, d, J ) 13.0 Hz), 5.84 (1H,
brs), 6.89 (1H, dd, J ) 7.4 Hz), 7.11 (1H, d, J ) 7.4 Hz), 7.20
(1H, dd, J ) 7.4 Hz), 7.52 (2H, brs); 13C NMR (125 MHz,
CDCl3) δ 31.2, 31.5, 34.0, 38.9, 43.6, 61.7, 119.3, 127.3, 128.7,
129.7, 133.3, 139.3, 140.6, 142.2, 149.8, 151.1; MS (EI) m/z 526
(
130Te, M+ + 1), 524 (128Te, M+ + 1), 509, 280, 265, 245, 231,
134, 91, 57; UV (cyclohexane) λmax 306 (sh, ꢀ 2.07 × 103), 232
(sh, ꢀ 2.18 × 104), 213 (ꢀ 3.59 × 104) nm. Anal. Calcd for C27H41
-
1
61.98; H, 7.90; N, 2.68. Found: C, 61.98; H, 7.51; N, 3.04. H
NMR, 13C NMR, IR, UV, and MS spectra were almost same
with those of racemic one.
NOTe: C, 61.98; H, 7.90; N, 2.68. Found: C, 61.47; H, 8.01;
N, 2.62.
HP LC An a lysis of Tellu r oxid es 1a -c a n d 2a -c. The
HPLC analysis of telluroxides 1a -c was performed on a Daicel
Chiralpak AS (250 × 4.6 mm) packed with amylose carbamate
derivative/silica gel using hexane containing 2-10 vol % of
isopropyl alcohol as a mobile phase at a flow rate of 1.0 mL
min-1. The HPLC analysis of telluroxides 2a -c was performed
on a Daicel Chiralcel OD (250 × 4.6 mm) packed with cellulose
carbamate derivative/silica gel using hexane containing 5-30
vol % of isopropyl alcohol as a mobile phase at a flow rate of
1.0 mL min-1. The enantiomeric excess (ee) for each optically
active telluroxides 1a -c and 2a -c was determined by HPLC
with these columns in an analytical scale.
Com p ou n d (S)-(-)-2c. 40% ee; mp 136-139 °C; [R]D -66.1
(c 0.12, CHCl3), [R]435 -193.3 (c 0.12, CHCl3); CD (cyclohexane)
316 ([θ] -4.37 × 104), 273 ([θ] +3.15 × 104), 246 ([θ] -6.31 ×
104), 229 ([θ] +2.65 × 104), 219 ([θ] -6.91 × 102), 204 ([θ] +1.27
× 105) nm. Anal. Calcd for C27H41NOTe: C, 61.98; H, 7.90; N,
1
2.68. Found: C, 62.08; H, 7.61; N, 3.02. H NMR, 13C NMR,
IR, UV, and MS spectra were almost same with those of
racemic one.
Kin etic Stu d y for Ra cem iza tion of Op tica lly Active
Tellu r oxid es. Kinetic studies of optically active telluroxides
1b, 1c, 2b, and 2c for racemization were examined in solutions
(ca. 5 mM) at 26 ( 1 °C. The rate of racemization were
calculated based on their specific rotation and were plotted to
the first-order rate equation.
Op tica l Resolu tion of Tellu r oxid es 1a -c a n d 2a -c a t
a P r ep a r a tive Sca le. Typically, the racemic telluroxide (100
mg) in eluent (0.5 mL) was charged to same type of optically
active columns (Daicel Chiralpak AS: 250 × 10 mm, Daicel
Chiralcel OD: 250 × 10 mm) and eluted with hexane contain-
ing 5 (for 1a ), 5 (for 1b), 2 (for 1c), 40 (for 2a ), 30 (for 2b), and
Ack n ow led gm en t. We thank Prof. R. Okazaki and
Prof. N. Tokitoh (The University of Tokyo) for synthe-
sizing 2,4,6-tris[bis(trimethylsilyl)methyl]benzene and
Mr. A. Ohnishi (Daicel Chemical Industries. Ltd. Tsuku-
ba Research Center) for testing the optical resolution
of the telluroxides by means of optically active columns.
This work was financially supported in part by a Grant-
in-Aid for Scientific Research on Priority Area and
General Scientific Research from the Ministry of Educa-
tion, Science, Sports, and Culture of J apan.
5 (for 2c) vol % isopropyl alcohol at flow rate of 1.0 mL min-1
.
Finally, ca. 15 mg of optically active telluroxides 1c, 2b, and
2c were obtained from the first eluent by repeated resolution
(2-3 times) and ca. 10 mg from the second eluent by repeated
resolution (usually, 4-5 times), respectively.
Com p ou n d (R)-(+)-1c. 100% ee; mp 96-97 °C; [R]D +25.3
(c 0.22, CHCl3), [R]D +22.5 (c 0.36, MeCN), [R]435 +129.6 (c
0.22, CHCl3), [R]435 +54.7 (c 0.36, MeCN); CD (MeCN) 313 ([θ]
+1.7 × 104), 286 ([θ] -1.5 × 104), 264 ([θ] +1.9 × 104), 246
([θ] -3.1 × 104), 236 (sh, [θ] -2.1 × 104), 212 ([θ] -1.2 × 105)
J O991721N