Thermodinamically Stabilized Chiral Chalcogen Oxides: Optical Resolution and Stereochemistry

Article abstract of DOI:10.1002/hc.1037

Optical resolution of racemic selenoxides, 1a, 1b, and 1c, and telluroxide 2b, possessing an 8-dimethylamino-1-naphthyl group by liquid chromatography using opytically active columns afforded the corresponding enantiomerically pure stereoisomers. Absolute

Full text of DOI:10.1002/hc.1037

Heteroatom Chemistry
Volume 12, Number 4, 2001
Thermodynamically Stabilized Chiral
Chalcogen Oxides: Optical Resolution
and Stereochemistry
Hideo Taka, Akikuni Matsumoto, Toshio Shimizu,
and Nobumasa Kamigata
Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minami-
ohsawa, Hachioji, Tokyo 192-0397, Japan
Received 17 November 2000; revised 16 January 2001
by bulky substituents (kinetic stabilization) because
the racemization of selenoxides and telluroxides had
been considered to be very rapid. The kinetic stabi-
lization was found to be effective; however, these
chalcogen oxides were still unstable toward race-
mization, especially the optically active telluroxide,
which racemized easily in solutions. Thermody-
namic stabilization is also considered to be effective
to stabilize unstable compounds, and there are many
reports concerning stabilization by intramolecular
coordination of an amino group [6]. For example,
reactive and unstable divalent organoselenium and
ABSTRACT: Optical resolution of racemic selenox-
ides, 1a, 1b, and 1c, and telluroxide 2b, possessing an
8-dimethylamino-1-naphthyl group by liquid chro-
matography using optically active columns afforded
the corresponding enantiomerically pure stereoiso-
mers. Absolute configurations of the optically active
chalcogen oxides were assigned by comparison of their
specific rotations and CD spectra with those of the sul-
fur analog. All of the optically active chalcogen oxides
obtained were stable toward racemization in their
solid states; however, selenoxides 1a and 1b and tel-
luroxide 2b racemized in solutions. Kinetic studies of
tellurium compounds [7–18], such as selenenyl [7–
11] and tellurenyl [12–18] halides, selenolates [7,9–
11], and tellurolates [12–18], have been isolated by
using the stabilization by intramolecular coordina-
tion. Recently, we reported the isolation of optically
active selenoxides [19] and telluroxides [20] possess-
ing the 2-(N,N-dimethylaminomethyl)phenyl group;
however, their configurational stabilities were not
satisfactory in solutions, although the intramolecu-
lar coordination of the amino group to the chalcogen
atoms certainly retarded the racemization.
We synthesized selenoxides and telluroxides
possessing the 8-dimethylamino-1-naphthyl group,
which are expected to facilitate the intramolecular
coordination due to the restricted geometries of the
molecules and we isolated the stereoisomers. In this
article, optical resolution of the selenoxides and tel-
luroxides by means of HPLC using optically active
the racemization clarified that thermodynamic stabi-
lization by intramolecular coordination of the nitro-
gen atom in the 8-dimethylamino-1-naphthyl group to
the chalcogen atom was effective to prevent the race-
mization. ᭧ 2001 John Wiley & Sons, Inc. Hetero-
atom Chem 12:227–237, 2001
INTRODUCTION
Our recent interest has focused on the synthesis and
stereochemistry of optically active tricoordinate se-
lenium and tellurium compounds [1–3]. Previously,
we reported the isolation of optically active selenox-
ides [1,4] and telluroxides [5], which are stabilized
Dedicated to Prof. Naoki Inamoto.
Correspondence to: Nobumasa Kamigata.
᭧ 2001 John Wiley & Sons, Inc.
227

228 Taka et al.
columns and their configurational stabilities will be
reported [21].
RESULTS AND DISCUSSION
Preparation of Racemic Selenoxides and
Telluroxides
Optical Resolution of Selenoxides and
Telluroxides by Means of HPLC Using Optically
Active Columns
8-Dimethylamino-1-naphthyl methyl selenide (3a),
precursor of selenoxide 1a, was prepared in 53%
yield by the reaction of 8-dimethylamino-1-naph-
thyllithium (4) with selenium powder followed by
treatment with methyl iodide, as shown in Scheme
1 [22]. Diaryl selenides 3b and 3c and tellurides 5a
and 5b were also synthesized by reacting the lithium
reagent 4 with the corresponding diselenides or di-
tellurides in yields of 46, 41, 49, and 11%, respec-
tively. Finally, racemic selenoxides 1a, 1b, and 1c and
telluroxides 2a and 2b were obtained in 82–98%
yields by oxidation [19,22] of the corresponding se-
lenides or tellurides with tert-butyl hypochlorite, fol-
lowed by treatment with aqueous sodium hydroxide.
Optical resolution of racemic selenoxide 1a was at-
tempted by HPLC at an analytical scale using an op-
tically active column packed with amylose carba-
mate derivative/silica gel (Daicel Chiralpak AS). As
shown in Figure 1, selenoxide 1a was resolved into
two peaks corresponding to each enantiomer
(eluent: hexane/ethanol ס 90/10). Similarly, racemic
selenoxide 1b (eluent: hexane/ethanol ס 90/10) and
1c (eluent: hexane/2-propanol ס 99/1) could also be
resolved into the enantiomeric isomers, respectively.
Racemic telluroxides 2a and 2b were also sub-
jected to HPLC using optically active columns at an
analytical scale. Telluroxide 2b was resolved into two
peaks corresponding to each enantiomer on Chiral-
cel OD (packed with cellulose carbamate derivative/
silica gel; eluent: hexane/2-propanol ס 75/25), as
shown in Figure 2. However, the first peak of the
chromatogram did not return to the base line, and
the phenomenon indicates that racemization is oc-
curring in the column. When the chromatographic
resolution was carried out under cooling the column
to מ3ЊC, telluroxide 2b could be resolved completely.
On the other hand, resolution of telluroxide 2a was
insufficient on Chiralcel OD (eluent: hexane/ethanol
ס 90/10), and 2a also could not be resolved on Chir-
alpak AS.
The optical resolution of racemic selenoxides 1a,
1b, and 1c was carried out at a preparative scale on
Daicel Chiralpak AS. Repeated resolution of the first
and second fractions of selenoxide 1a gave optically
pure selenoxides, respectively, the optical purities of
which were determined by HPLC analysis. The first
eluted enantiomer had a positive specific rotation
{(ם)-1a: enantiomeric excess (ee) 100%; [␣]D ם363.8
(c 0.10, CHCl3)}, and the second eluted enantiomer
had a negative one {(מ)-1a: ee 100%; [␣]D מ350.8 (c
0.19, CHCl3)}. Similarly, optically pure selenoxides
(מ)-1b and (מ)-1c were obtained from the first frac-
tions. However, (ם)-1b and (ם)-1c, collected from
the second fractions, were 80 and 90% ee, respec-
tively. The results are summarized in Table 1. The
reason why optically pure selenoxides (ם)-1b and
SCHEME 1 Reagents and Conditions: i: BuLi, ether, r.t.; ii:
Se powder, then MeI; iii: (PhSe)2; iv: (TipSe)2; v: (PhTe)2; vi:
(TipTe)2; vii: ButOCl, MeOH, CH2Cl2, מ25ЊC, then NaOH(aq.)

Thermodynamically Stabilized Chiral Chalcogen Oxides: Optical Resolution and Stereochemistry 229
FIGURE 1 Chromatographic resolution of racemic selenoxides 1a, 1b, and 1c by means of HPLC using an optically active
column (Daicel Chiralpak AS) at room temperature.
FIGURE 2 Chromatographic resolution of racemic telluroxides 2a and 2b by means of HPLC using an optically active column
(Daicel Chiralcel OD) at room temperature. *At מ3ЊC.
TABLE 1 Chromatographic Resolution of Selenoxides and Telluroxides
First enantiomer
[␣]D (c)c
Second enantiomer
Compound
Columna
Alcohol/%b
ee/%d
[␣]D (c)
ee/%
1a
1b
1c
2b
AS
AS
AS
OD
10e
10e
1f
ם363.8 (0.10)
מ165.4 (0.19)
מ87.6 (0.58)
מ46.0 (0.67)
100
100
100
100
מ350.8 (0.19)
ם140.5 (0.50)
ם78.7 (0.31)
ם47.6 (0.23)
100
80
90
25f
100
aAS, Daicel Chiralpak AS; OD, Daicel Chiralcel OD.
bThe volume percentage of ethanol or 2-propanol in hexane used as mobile phase.
cSpecific rotations were taken in chloroform at 25–27ЊC.
dOptical purities were determined by HPLC analysis.
eEthanol.
f2-Propanol.
(ם)-1c could not be obtained may be due to tailing
of the first eluted enantiomer.
tically active telluroxides (מ)-2a and (ם)-2a could
not be obtained, perhaps due to racemization that
was occurring in the column.
The optical resolution of racemic telluroxides 2a
and 2b was also carried out by using an optically
active column (Daicel Chiralcel OD) at a preparative
scale at מ3ЊC. In the case of 2b, repeated resolution
of the first and second fractions gave the optically
pure stereoisomers, respectively. The first eluted en-
antiomer had a negative specific rotation, and the
second enantiomer had a positive one. However, op-
Circular Dichroism Spectra and Absolute
Configurations of Optically Active Selenoxides
and Telluroxides
The CD spectra of optically active selenoxides (ם)-
1a, (ם)-1b, and (ם)-1c, showed negative first Cotton

230 Taka et al.
effects at 317, 314, and 283 nm, respectively, and
those of (מ)-1a, (מ)-1b, and (מ)-1c showed positive
Cotton effects in the same regions, as shown in Fig-
ure 3. The positive first Cotton effects of the (מ)-
selenoxides correspond well with that of optically ac-
tive (S)-(מ)-8-dimethylamino-1-naphthyl 4Ј-tolyl
sulfoxide {(S)-(מ)-6}, which was prepared by react-
ing (S)s-(מ)-menthyl-(מ)-4-toluenesulfinate with
lithium reagent 4 according to the modified Ander-
sen’s method [23,24]. Therefore, the absolute config-
uration of selenoxides (מ)-1a, (מ)-1b, and (מ)-1c
can be assigned to be the S-form, and that of (ם)-
1a, (ם)-1b, and (ם)-1c is R.
of water that remains in the solvent. However, in the
case of (מ)-1c, no racemization was observed, even
in methanol solution containing 20 vol % of water;
showing that the combination of the kinetic and
thermodynamic stabilization is effective to prevent
the racemization of optically active selenoxides.
We had already reported that (S)-(מ)-2-(N,N-di-
methylaminomethyl)phenyl methyl selenoxide {(S)-
(מ)-7} and (S)-(מ)-2-(N,N-dimethylaminometh-
yl)diphenyl selenoxide {(S)-(מ)-8} were stabilized
toward racemization by intramolecular coordina-
tion of the amino group to the selenium atom [19].
The rate constants of racemization for selenoxides
(S)-(מ)-7 and (S)-(מ)-8 in methanol solutions were
2.28 ן 10מ4 and 5.58 ן 10מ6 sמ1, respectively. There-
fore, selenoxide 1a is more stable toward racemiza-
tion in methanol solution than selenoxide 7, and se-
lenoxide 1b is also more stable than selenoxide 8.
These results show that the thermodynamic stabili-
zation of selenoxide by the intramolecular coordi-
nation of the amino group of 8-dimethylamino-1-
naphthyl moiety to the selenium atom is more
effective due to the restricted geometry than that of
the 2-(N,N-dimethylaminomethyl)phenyl group.
The CD spectrum of optically active telluroxide
(ם)-2b also showed a negative first Cotton effect at
339 nm, and that of (מ)-2b showed a positive Cotton
effect in the same region, as shown in Figure 4. The
absolute configuration of optically active telluroxide
(מ)-2b was estimated to be the S-form by comparing
the first Cotton effect with that of (S)-(מ)-6.
Configurational Stability of Optically Active
Selenoxides and Telluroxides
Optically active selenoxides 1a, 1b, and 1c and tel-
luroxide 2b were stable toward racemization in the
solid states even after two weeks when they were
kept in a desiccator at room temperature. Selenox-
ides (ם)-1a, (ם)-1b, and (מ)-1c were also stable in
chloroform, and no racemization was observed after
5 days; however, (ם)-1a and (ם)-1b racemized in
methanol solutions despite the careful purification
of the solvent. On the other hand, selenoxide (מ)-1c,
having a bulky substituent, the 2,4,6-triisopropyl-
phenyl group, was stable not only in chloroform but
also in methanol. The rates of racemization for op-
tically active selenoxides (ם)-1a and (ם)-1b in meth-
anol showed a good linear relationship in first-order
The racemization of optically active telluroxide
(ם)-2b was observed, not only in methanol but also
even in carefully purified and dried chloroform,
whereas the corresponding optically active selenox-
ide (מ)-1c did not racemize under these conditions,
and the kinetics for racemization was also examined.
The rate for the racemization of (ם)-2b also showed
a good linear relationship in first-order rate plots,
מ5 מ1
and the rate constant was 9.08 ן 10
s
at 26ЊC.
Telluroxide 2b is slightly more stable toward race-
mization in chloroform than is (R)-(ם)-2-(N,N-
dimethylaminomethyl)phenyl
phenyl telluroxide {(R)-(ם)-9}
2,4,6-triisopropyl-
[20]. The
intramolecular coordination of the amino group of
the 8-dimethylamino-1-naphthyl moiety might be
more effective to a certain extent than that of the 2-
(N,N-dimethylaminomethyl)phenyl moiety; how-
ever, it was not enough to meet our initial expecta-
tion. Thus, telluroxide 2b racemized completely
within 1 minute in methanol solutions.
מ5
rate plots, and the rate constants were 1.84 ן 10
מ6 מ1
and 2.21 ן 10
s
(at 26ЊC), respectively, as sum-
marized in Table 2. Addition of water to the metha-
nol solution of (ם)-1a and (ם)-1b accelerated the
racemization. These results indicate that the race-
mization of selenoxide occurs due to a trace amount

Thermodynamically Stabilized Chiral Chalcogen Oxides: Optical Resolution and Stereochemistry 231
FIGURE 3 CD spectra of optically active selenoxides (ם)- 1a–c and (מ)-1a–c, and sulfoxide (S)-(מ)-6 in cyclohexane.
underwent racemization faster than selenoxides in
solutions. Selenoxide 1c, stabilized by the intramo-
lecular coordination and bulky substituent, was very
stable toward racemization even in solutions con-
taining water. Selenoxide 1b was more stable toward
racemization than selenoxide 8, and telluroxide 2b
was also more stable than telluroxide 9. These re-
sults show that the coordination of the amino group
of the 8-dimethylamino-1-naphthyl moiety to the
chalcogen atom is more effective than that of the 2-
CONCLUSION
(N,N-dimethylaminomethyl)phenyl group since the
naphthyl group is considered to facilitate better in-
tramolecular coordination due to the restricted
geometry.
Thermodynamically stabilized optically pure sele-
noxides 1a, 1b, and 1c and telluroxide 2b possessing
an 8-dimethylamino-1-naphthyl substituent were
isolated by means of HPLC using optically active col-
umns. These optically active chalcogen oxides were
stable toward racemization in the solid state but ra-
cemized in solutions. Optically active telluroxides
EXPERIMENTAL
Tetrahydrofuran (THF) was distilled from sodium
benzophenone ketyl before use. Cyclohexane,

232 Taka et al.
and 7.56–7.66 (2 H, m, Ar-H); dC (125 MHz; CDCl3;
Me4Si) 7.2, 45.9, 119.0, 123.6, 124.8, 125.7, 125.8,
126.1, 129.9, 131.5, 135.8, and 151.6; m/z (EI) 265
ם
ם
(80Se, M ), 263 (78Se, M ), 250, 235, 168, 155, 127,
115, and 84.
8-Dimethylamino-1-naphthyl Methyl Selenoxide
(1a)
Selenide 3a (2.64 g, 10.0 mmol) was oxidized with
tert-butyl hypochlorite (1.30 g, 12.0 mmol) to give
racemic selenoxide 1a (2.31 g, 82%) according to the
procedures in the literature [22]; m.p. 123–125ЊC (lit.
128–129ЊC, decomp.) [22]; kmax (cyclohexane)/nm
מ1
מ3
292 (e/dm3 mol cm 5.1 ן 103) and 224 (2.9 ן
104); mmax (KBr)/cm 2960, 2360, 1360, and 830; dH
מ1
(500 MHz; CDCl3; Me4Si) 2.55 (3 H, s, SeMe), 2.60 (3
H, s, NMe), 2.88 (3 H, s, NMe), 7.48 (1 H, d, J 7.3,
Ar-H), 7.55 (1 H, dd, J 7.9 and 7.9, Ar-H), 7.73 (1 H,
dd, J 7.3 and 7.3, Ar-H), 7.80 (1 H, d, J 7.9, Ar-H),
7.98 (1 H, d, J 7.9, Ar-H) and 8.64 (1 H, d, J 7.3, Ar-
H); dC (125 MHz, CDCl3, Me4Si) 39.3, 42.8, 49.0,
119.3, 124.6, 126.1, 126.3 (ן2), 127.1, 130.7, 135.2,
FIGURE 4 CD spectra of optically active telluroxides (ם)-
2b and (מ)-2b in cyclohexane.
chloroform, dichloromethane, hexane and 2-pro-
panol were distilled from calcium hydride before
use. Methanol and ethanol were distilled from mag-
nesium cake and stored with 3A molecular sieves un-
der nitrogen. Thin-layer chromatography (TLC) was
performed with Merck Art. 5554 DC-Alufolien Kie-
selgel 60 F254. Column chromatography was per-
formed with Merck 7734 Kieselgel 60.
ם
137.6 and 148.8; m/z (EI) 281 (80Se, M ), 279 (78Se,
ם
M ), 264, 249, 235, 168, 127, and 86.
8-Dimethylamino-1-naphthyl Phenyl Selenide
(3b)
To a stirred suspension of 8-dimethylamino-1-naph-
thyllithium (4), prepared from N,N-dimethyl-1-
naphthylamine (8.56 g, 50.0 mmol) and BuLi (1.53
M in hexane; 36.0 mL, 55.0 mmol) in anhydrous
ether (150 mL), was added an anhydrous ether so-
lution (100 mL) of diphenyldiselenide (15.6 g, 50.0
mmol) under nitrogen at room temperature. The so-
lution was stirred for an additional 2 hours. Satu-
rated brine (50 mL) was added to the solution, and
the organic layer was separated. The organic com-
ponent remaining in the aqueous layer was extracted
with ether (50 mL ן 3), and the combined organic
layer was washed with water and dried over anhy-
drous magnesium sulfate. The solution was concen-
trated under reduced pressure, and purification by
silica gel column chromatography (eluent: hexane/
ether ס 2/1) gave selenide 3b (7.45 g, 46%); m.p. 92–
8-Dimethylamino-1-naphthyl Methyl Selenide
(3a)
To a stirred suspension of 8-(dimethylamino-1-naph-
thyl)lithium (4), prepared from N,N-dimethyl-1-
naphthylamine (8.56 g, 50.0 mmol) and BuLi (1.53
M in hexane; 36.0 mL, 55.0 mmol) in anhydrous
ether (150 mL), was added elemental selenium (3.9
g, 50.0 mmol) under nitrogen. After 1 hour, all of the
selenium powder had been consumed to give a lith-
ium naphthaleneselenolate, to which then was
added an ether solution (20 mL) of methyl iodide
(9.2 g, 65.0 mmol). The solution was stirred for an
additional 2 hours. Saturated brine (100 mL) was
added to the solution, and the organic layer was
separated. The organic component remaining in the
aqueous layer was extracted with ether (100 mL ן
3), and the combined organic layer was washed with
water and dried over anhydrous magnesium sulfate.
The solution was concentrated under reduced pres-
sure, and purification by silica gel column chroma-
tography (eluent: hexane/ether ס 2/1) gave selenide
3a (6.98 g, 53%); m.p. 73–76ЊC (from benzene-hex-
ane) (lit. 45ЊC) [22]; mmax (KBr)/cmמ1 2360, 1560, 860,
and 820; dH (500 MHz; CDCl3; Me4Si) 2.14 (3 H, s,
SeMe), 2.68 (6 H, s, NMe2), 7.28–7.44 (4 H, m, Ar-H),
מ1
93ЊC; mmax (KBr)/cm 2970, 2350, 1700, and 820; dH
(500 MHz, CDCl3, Me4Si) 2.76 (6 H, s, NMe2), 6.87–
6.94 (1 H, m, Ar-H), 7.03–7.14 (1 H, m, Ar-H), 7.35–
7.45 (5 H, m, Ph), 7.52–7.65 (2 H, m, Ar-H) and 7.73–
7.80 (2 H, m, Ar-H); dC (125 MHz; CDCl3; Me4Si) 46.1,
119.1, 125.1, 125.76, 125.79, 125.9, 126.1, 128.4,
129.39, 129.43, 132.79, 132.84, 135.9, 137.5, and
ם
ם
151.5; m/z (EI) 327 (80Se, M ), 325 (78Se, M ), 265,
250, 170, 154, and 84.

Thermodynamically Stabilized Chiral Chalcogen Oxides: Optical Resolution and Stereochemistry 233
TABLE 2 First-Order Rate Constants for Racemization of Optically Active Selenoxides and Telluroxides in Solutionsa
k/sמ1 (t1/2/h)
Solvent
(R)-(ם)-1a
(R)-(ם)-1b
(S)-(מ)-1c
(R)-(ם)-2b
(S)-(מ)-7b
(S)-(מ)-8b
(R)-(ם)-9c
מ5
מ4
CHCl3
MeOH
Ae
A
A
A
A
9.08 ן 10
(2.12)
Bf
A
A
1.36 ן 10
(1.41)
B
מ5
מ6
מ4
מ6
1.84 ן 10
(10.4)
5.21 ן 10
(3.70)
2.21 ן 10
(87.1)
3.70 ן 10
(51.9)
2.28 ן 10
(0.844)
1.23 ן 10
(0.157)
5.58 ן 10
(34.5)
מ5
מ5
מ6
מ3
MeOH
/H2Od
B
5.13 ן 10
(3.76)
B
aIn ca. 5 mM solution at 26 ע 1ЊC.
bRef. [19].
cRef. [20].
dMeOH/H2O ס 4/1.
eA, No racemization was observed even after 5 days.
f B, Racemization was completed within 1 minute.
8-Dimethylamino-1-naphthyl Phenyl Selenoxide
naphthylamine (4.28 g, 25.0 mmol) and BuLi (1.53
M in hexane; 18.0 mL, 27.5 mmol) in anhydrous
ether (75 mL), was added an anhydrous ether solu-
tion (75 mL) of bis(2,4,6-triisopropylphenyl)di-
selenide (14.1 g, 25.0 mmol) under nitrogen at room
temperature. The solution was stirred for an addi-
tional 2 hours. Saturated brine (50 mL) was added
to the solution, and the organic layer was separated.
The organic component remaining in the aqueous
layer was extracted with ether (50 mL ן 3). The
combined organic layer was washed with water, and
dried over anhydrous magnesium sulfate. The solu-
tion was concentrated under reduced pressure, and
purification by silica gel column chromatography
(eluent: hexane/ether ס 2/1) gave selenide 3c (4.64
g, 41%); m.p. 119–122ЊC; mmax (KBr)/cmמ1 2960, 2340,
1560, and 820; dH (500 MHz, CDCl3, Me4Si) 1.11 (6
H, br s, CHMe2), 1.20 (6 H, br s, CHMe2), 1.32 (6 H,
d, J 7.0, CHMe2), 2.80 (6 H, s, NMe2), 2.96 (1 H, sep,
J 7.0, CHMe2), 3.74 (2 H, sep, J 7.0, CHMe2), 6.75 (1
H, d, J 7.6, Ar-H), 7.07 (1 H, dd, J 7.6 and 7.6, Ar-H),
7.13 (2 H, s, Ar-H), 7.35–7.43 (2 H, m, Ar-H), 7.50 (1
H, d, J 7.6, Ar-H) and 7.61 (1 H, d, J 7.6, Ar-H); dC
(125 MHz; CDCl3; Me4Si) 24.0, 25.2, 33.8, 34.3, 46.2,
118.6, 121.8, 124.7, 125.65, 125.70, 125.8, 126.1,
129.52, 129.54, 133.7, 136.1, 149.9, 151.7, and 154.0;
(1b)
To a stirred mixed solvent of dichloromethane (200
mL) and methanol (50 mL) containing selenide 3b
(3.27 g, 10.0 mmol) was added slowly a dichloro-
methane solution (50 mL) of tert-butyl hypochlorite
(1.30 g, 12.0 mmol) at מ25ЊC under nitrogen, and
the solution was stirred for an additional 30 minutes
and then was allowed to stand until it attained room
temperature. After aqueous sodium hydroxide (0.60
g in 20 mL) was poured into the stirred reaction mix-
ture, the organic layer was separated. The organic
component remaining in the aqueous layer was ex-
tracted with dichloromethane (50 mL ן 3), and
combined with the organic layer and was dried over
anhydrous sodium sulfate. The solution was concen-
trated under reduced pressure, and purification by
silica gel column chromatography (eluent: dichlo-
romethane/methanol ס 100/6) gave racemic sele-
noxide 1b (3.28 g, 88%); m.p. 152–155ЊC; kmax (cyclo-
מ1
מ3
hexane)/nm 295 (e/dm3 mol cm 4.5 ן 103) and
218 (2.6 ן 104); mmax (KBr)/cm 2980, 2360, 1440,
מ1
1360, and 815; dH (500 MHz; CDCl3; Me4Si) 2.13 (3
H, s, NMe), 2.51 (3 H, s, NMe), 7.13–7.18 (5 H, m,
Ph), 7.22 (1 H, d, J 7.4, Ar-H), 7.35 (1 H, dd, J 7.9 and
7.9, Ar-H), 7.66 (1 H, d, J 7.9, Ar-H), 7.69 (1H, dd, J
7.4 and 7.4, Ar-H), 7.92 (1H, d, J 7.9, Ar-H) and 8.77
(1H, d, J 7.4, Ar-H); dC (125 MHz, CDCl3, Me4Si) 43.2,
49.4, 119.3, 125.9, 126.1, 126.3, 126.6 (ן2), 127.7,
128.8, 129.8, 131.2, 134.2, 134.9, 145.7 and 148.9; m/
ם
ם
m/z (EI) 453 (80Se, M ), 451 (78Se, M ), 250, 170, 155,
and 84.
8-Dimethylamino-1-naphthyl 2Ј,4Ј,6Ј-
Triisopropylphenyl Selenoxide (1c)
ם
ם
z (EI) 343 (80Se, M ), 341 (78Se, M , 341.0527,
C18H17NO78Se requires 341.0483), 327, 235, 168, 121,
and 86.
To a stirred mixed solvent of dichloromethane (40
mL) and methanol (10 mL) containing selenide 3c
(0.91 g, 2.0 mmol) was added slowly a dichlorome-
thane solution (5 mL) of tert-butyl hypochlorite (0.26
g, 2.4 mmol) at מ25ЊC under nitrogen, and the so-
lution was stirred for an additional 30 minutes and
8-Dimethylamino-1-naphthyl 2Ј,4Ј,6Ј-
Triisopropylphenyl Selenide (3c)
To a stirred suspension of 8-dimethylamino-1-na-
phthyllithium (3), prepared from N,N-dimethyl-1-

234 Taka et al.
then was allowed to stand until it attained room tem-
perature. After aqueous sodium hydroxide (0.30 g in
10 mL) had been poured into the stirred reaction
mixture, the organic layer was separated. The or-
ganic component remaining in the aqueous layer
was extracted with dichloromethane (50 mL ן 3),
and the combined organic layer was dried over an-
hydrous sodium sulfate. The solution was concen-
trated under reduced pressure, and purification by
silica gel column chromatography (eluent: dichlo-
romethane/methanol ס 100/6) gave racemic sele-
noxide 1c (0.83 g, 88%); m.p. 117–118ЊC; kmax (cyclo-
2.78 (6 H, s, NMe2), 7.07–7.15 (2 H, m, Ph), 7.31–7.35
(2 H, m, Ar-H), 7.39–7.45 (3 H, m, Ph), 7.56–7.60 (1
H, m, Ar-H), 7.63–7.68 (1 H, m, Ar-H) and 7.97–8.00
(2 H, m, Ar-H); dC (125 MHz; CDCl3; Me4Si) 47.2,
116.0, 119.0, 122.6, 125.5, 125.9, 126.6, 126.9, 128.1,
129.3, 130.9, 131.5, 135.4, 141.2, and 150.6; m/z (EI)
ם
ם
377 (130Te, M ), 375 (128Te, M ), 300, 170, 155, 127,
and 77.
8-Dimethylamino-1-naphthyl Phenyl Telluroxide
(2a)
מ1
מ3
hexane)/nm 302 (e/dm3 mol cm 7.3 ן 103) and
To a stirred dichloromethane solution (50 mL) con-
taining telluride 5a (0.75 g, 2.0 mmol) and methanol
(1 mL) was added slowly a dichloromethane solution
(5 mL) of tert-butyl hypochlorite (0.26 g, 2.4 mmol)
at מ25ЊC under nitrogen, and the solution was
stirred for an additional 30 minutes and was allowed
to stand until it attained room temperature. After
aqueous sodium hydroxide (0.30 g in 20 mL) had
been poured into the stirred reaction mixture, the
organic layer was separated. The organic component
remaining in the aqueous layer was extracted with
dichloromethane (50 mL ן 3), and the combined
organic layer was dried over anhydrous sodium sul-
fate. The solution was concentrated under reduced
pressure, and purification by silica gel column chro-
matography (eluent: dichloromethane/methanol ס
100/6) gave racemic telluroxide 2a (0.77 g, 98%);
מ1
208 (5.6 ן 104); mmax (KBr)/cm 2970, 2360, 1460,
1360, and 830; dH (500 MHz, CDCl3, Me4Si) 0.85 (6
H, d, J 6.7, CHMe2), 1.20 (6 H, d, J 6.7, CHMe2), 1.21
(6 H, d, J 6.7, CHMe2), 2.26 (3 H, s, NMe), 2.77 (3 H,
s, NMe), 2.81 (1 H, sep, J 6.7, CHMe2), 3.56 (2 H, sep,
J 6.7, CHMe2), 6.97 (2 H, s, Ar-H), 7.39 (1 H, d, J 7.6,
Ar-H), 7.47 (1 H, dd, J 7.6 and 7.6, Ar-H), 7.67 (1 H,
dd J 7.6 and 7.6, Ar-H), 7.75 (1 H, d, J 7.6, Ar-H), 7.97
(1 H, d, J 7.6, Ar-H) and 8.65 (1 H, d, J 7.6, Ar-H); dC
(125 MHz, CDCl3, Me4Si) 23.76, 23.83, 23.9, 24.8,
29.5, 34.1, 44.6, 48.1, 119.3, 122.5, 126.0, 126.3,
128.3, 128.4, 131.2, 135.6, 137.7, 139.4, 150.0, 150.3,
and 151.0; dC (125 MHz, C6D6, Me4Si) 23.9, 24.0, 24.1,
25.0, 29.8, 34.5, 44.1, 48.3, 119.1, 122.6, 126.1, 126.4,
128.3, 128.9, 129.0, 131.2, 136.0, 139.9, 141.5, 150.6,
ם
150.9, and 151.0 [25]; m/z (EI) 469 (80Se, M ), 467
ם
מ1
(78Se, M , 467.1898, C27H35NO78Se requires
m.p. 106–109ЊC; mmax (KBr)/cm 2980, 2360, 1440,
467.1892), 453, 250, 168, 127, and 91.
1360, and 815; dH (500 MHz, CDCl3, Me4Si) 2.38 (3
H, s, NMe), 2.72 (3 H, s, NMe), 7.18–7.37 (5 H, m,
Ph), 7.39 (1H, d, J 7.3, Ar-H), 7.51 (1 H, dd, J 8.0 and
8.0, Ar-H), 7.84 (1 H, d, J 8.0, Ar-H), 7.86 (1 H, dd, J
7.3 and 7.3, Ar-H), 8.07 (1 H, d, J 8.0, Ar-H) and 8.84
(1 H, d, J 7.3, Ar-H); dC (125 MHz; CDCl3; Me4Si) 44.4,
49.6, 119.3, 126.4, 126.9, 127.1, 128.1, 129.4, 130.0,
130.5, 130.7, 131.1, 131.5, 135.3, 139.8, and 149.0;
8-Dimethylamino-1-naphthyl Phenyl Telluride
(5a)
To a stirred suspension of 8-dimethylamino-1-naph-
thyllithium (4), prepared from N,N-dimethyl-1-
naphthylamine (4.28 g, 25.0 mmol) and BuLi (1.53
M in hexane; 18.0 mL, 27.5 mmol) in anhydrous
ether (75 mL), was added an anhydrous ether solu-
tion (75 mL) of diphenylditelluride (10.2 g, 25.0
mmol) under nitrogen at room temperature. The so-
lution was stirred for an additional 2 hours. Satu-
rated brine (150 mL) was added to the solution, and
the organic layer was separated. The organic com-
ponent remaining in the aqueous layer was extracted
with ether (50 mL ן 3). The combined organic layer
was washed with water, and then dried over anhy-
drous magnesium sulfate. The solution was concen-
trated under reduced pressure, and purification by
silica gel column chromatography (eluent: hexane/
ether ס 2/1) gave telluride 5a (4.59 g, 49%); m.p.
ם
m/z (EI) 393 (130Te, M , 393.0382, C18H17NO130Te re-
ם
quires 393.0377), 391 (128Te, M ), 377, 300, 170, 155,
127, and 77.
8-Dimethylamino-1-naphthyl 2Ј,4Ј,6Ј-
Triisopropylphenyl Telluride (5b)
To a stirred suspension of 8-dimethylamino-1-naph-
thyllithium (4), prepared from N,N-dimethyl-1-
naphthylamine (8.56 g, 50.0 mmol) and BuLi (1.53
M in hexane; 36.0 mL, 55.0 mmol) in anhydrous
ether (150 mL), was added an anhydrous ether so-
lution (100 mL) of bis(2,4,6-triisopropylphenyl)
ditelluride (33.0 g, 50.0 mmol) under nitrogen at
room temperature. The solution was stirred for an
additional 30 minutes. Saturated brine (50 mL) was
מ1
119–122ЊC (lit. 119ЊC) [18]; mmax (KBr)/cm 2970,
2350, 1700, and 820; dH (500 MHz, CDCl3, Me4Si)

Thermodynamically Stabilized Chiral Chalcogen Oxides: Optical Resolution and Stereochemistry 235
added to the solution, and the organic layer was
47.8, 119.6, 122.6, 126.3, 126.8, 126.9, 130.1, 130.3,
131.2, 132.2, 135.3, 136.7, 149.5, 151.6, and 153.5;
separated. The organic component remaining in the
aqueous layer was extracted with ether (50 mL ן 3),
and the combined organic layer was washed with
water and dried over anhydrous magnesium sulfate.
The solution was concentrated under reduced pres-
sure, and purification by silica gel column chroma-
tography (eluent: hexane/ether ס 2/1) gave telluride
ם
m/z (EI) 519 (130Te, M , 519.1798, C27H35NO130Te re-
ם
quires 519.1781), 518 (128Te, M ם 1), 502, 300, 170,
155, 127, and 91.
High-Performance Liquid Chromatography
(HPLC) Analysis of Selenoxides 1a, 1b, and 1c
and Telluroxides 2a and 2b Using Optically
Active Columns
מ1
5b (2.85 g, 11%); m.p. 129–131ЊC; mmax (KBr)/cm
2975, 1580, 1460, 1130, 875, and 740; dH (500 MHz;
CDCl3; Me4Si) 1.12 (6 H, br s, CHMe2), 1.23 (6 H, br
s, CHMe2), 1.32 (6 H, d, J 7.8, CHMe2), 2.83 (6 H, s,
NMe2), 2.96 (1 H, sep, J 7.8, CHMe2), 3.80 (2 H, sep,
J 7.8, CHMe2), 7.00–7.10 (2 H, m, Ar-H), 7.13 (2 H,
s, Ar-H), 7.42–7.47 (2 H, m, Ar-H), 7.75–7.63 (1 H, m,
Ar-H), and 7.63–7.71 (1 H, m, Ar-H); dC (125 MHz,
CDCl3, Me4Si) 24.0, 24.6, 25.4, 34.2, 39.0, 47.3, 117.6,
118.8, 121.0, 125.48, 125.54, 126.5, 126.9, 127.0,
131.2, 131.9, 135.5, 149.9, 150.8, and 155.5; m/z (EI)
The HPLC analysis of selenoxides 1a–c was per-
formed on a Daicel Chiralpak AS (250 ן 4.6 mm)
packed with amylose carbamate derivative/silica gel
using hexane containing 10 vol % (for 1a and 1b) and
1 vol % (for 1c) of ethanol as a mobile phase at a flow
rate of 1.0 mL minמ1. The HPLC analysis of tellurox-
ides 2a and 2b was performed on a Daicel Chiralcel
OD (250 ן 10 mm) packed with cellulose carbamate
derivative/silica gel using hexane containing 10 vol
ם
ם
503 (130Te, M ), 501 (128Te, M ), 300, 221, 170, 155,
% of ethanol (for 2a) or 25 vol % of 2-propanol (for
and 71.
מ1
2b) as a mobile phase at a flow rate of 1.0 mL min
.
The enantiomeric excess (ee) for each optically ac-
tive selenoxide 1a, 1b, and 1c and telluroxide 2a and
2b was determined by HPLC with these optically ac-
tive columns in an analytical scale.
8-Dimethylamino-1-naphthyl 2Ј,4Ј,6Ј-
Triisopropylphenyl Telluroxide (2b)
To a stirred mixed solvent of dichloromethane (40
mL) and methanol (10 mL) containing telluride 5b
(1.50 g, 2.98 mmol) was added slowly a dichloro-
methane solution (10 mL) of tert-butyl hypochlorite
(0.39 g, 3.6 mmol) at מ25ЊC under nitrogen, the so-
lution was stirred for an additional 30 minutes and
allowed to stand until it attained room temperature.
After aqueous sodium hydroxide (0.40 g in 20 mL)
was poured into the stirred reaction mixture and the
organic layer was separated. The organic component
remaining in the aqueous layer was extracted with
dichloromethane (50 mL ן 3), and the combined
organic layer the was dried over anhydrous sodium
sulfate. The solution was concentrated under re-
duced pressure, and purification by silica gel column
chromatography (eluent: dichloromethane/metha-
nol ס 100/6) gave racemic telluroxide 2b (1.36 g,
88%); m.p. 180–182ЊC; kmax (cyclohexane)/nm 293 (e/
dm3 molמ1 cmמ3 1.2 ן 104), 229 (sh, 6.2 ן 104), and
Optical Resolution of Selenoxides 1a, 1b, and
1c and Telluroxides 2a and 2b at a Preparative
Scale
Typically, racemic selenoxide or telluroxide (50 mg)
in eluent (0.5 mL) was charged to the same type of
optically active columns (Daicel Chiralpak AS: 250
ן 10 mm or Daicel Chiralcel OD: 250 ן 10 mm) and
eluted with hexane containing 10 vol % ethanol for
1a, 1b, and 2a, 1 vol % 2-propanol for 1c and 25 vol
מ1
% 2-propanol for 2b at flow rate of 1.0 mL min
.
Finally, ca. 15 mg of optically active selenoxides 1a,
1b, and 1c and telluroxide 2b were obtained from
the first eluate by repeated resolution (2–3 times)
and ca. 10 mg from the second eluate by repeated
resolution (4–5 times), respectively.
Compound (ם)-1a. 100% ee; m.p. 140–141ЊC;
[␣]D ם 363.8 (c 0.10, in CHCl3), [␣]435 ם761.5 (c 0.10,
in CHCl3); CD (cyclohexane) nm 317 ([h] מ7.3 ן
103), 237 ([h] ם2.3 ן 105) and 214 ([h] מ7.1 ן 104)
מ1
212 (7.5 ן 104) nm; mmax (KBr)/cm 2975, 1450,
1360, 870, and 840; dH (500 MHz, CDCl3, Me4Si) 0.90
(6 H, d, J 6.8, CHMe2), 1.20 (6 H, d, J 6.8, CHMe2),
1.25 (6 H, d, J 6.8, CHMe2), 2.32 (3 H, s, NMe), 2.84
(1 H, sep, J 6.8, CHMe2), 2.86 (3 H, s, NMe), 3.60 (2
H, sep, J 6.8, CHMe2), 7.01 (2 H, s, Ar-H), 7.47–7.55
(2 H, m, Ar-H), 7.67 (1 H, dd, J 7.6 and 7.6, Ar-H),
7.79 (1 H, dd, J 7.6 and 1.6, Ar-H), 7.98 (1 H, d, J 7.6,
Ar-H) and 8.54 (1 H, d, J 7.0, Ar-H); dC (125 MHz;
CDCl3; Me4Si) 23.8, 24.3, 25.0, 25.4, 32.5, 34.2, 46.3,
ם
nm; m/z (EI) 281.0291 (80Se, M , C13H15NO80Se re-
quires 281.0319). 1H NMR, 13C NMR, IR, UV, and MS
spectra were almost the same as those of racemic
one.
Compound (מ)-1a. 100% ee: m.p. 143–145ЊC;
[␣]D מ350.8 (c 0.19, in CHCl3), [␣]435 מ752.9 (c 0.19,

236 Taka et al.
in CHCl3); CD (cyclohexane)/nm 318 ([h] ם7.0 ן
103), 237 ([h] מ2.3 ן 105) and 213 ([h] ם7.3 ן 104);
Synthesis of (S)-(מ)-8-Dimethylamino-1-
naphthyl 4Ј-Tolyl Sulfoxide [(S)-(מ)-6]
ם
m/z (EI) 279.0331 (78Se, M , C13H15NO78Se requires
To a stirred ether solution (15 mL) of (S)s-(מ)-men-
thyl-(מ)-4-toluenesulfinate [24] (100% ee; 0.29 g, 1.0
mmol) was added at 0ЊC 8-dimethylamino-1-naph-
thyllithium (4), prepared from N,N-dimethyl-1-
naphthylamine (0.17 g, 1.0 mmol) and BuLi (1.53 M
in hexane; 0.72 mL, 1.1 mmol) in anhydrous ether
(10 mL). After additional stirring for 1 hour at room
temperature, the mixture was poured into brine, and
the organic layer was separated. The organic com-
ponent remaining in the aqueous layer was extracted
with ether (100 mL ן 3), and the combined organic
layer was washed with water and dried over anhy-
drous magnesium sulfate. The solution was concen-
trated under reduced pressure, and purification by
silica gel column chromatography (eluent: dichlo-
romethane/methanol ס 100/6) gave (S)-(מ)-6 (0.26
g, 85%, 96% ee) as a pale yellow oil; kmax (cyclohex-
ane)/nm 298 (e/dm3 molמ1 cmמ3 5.3 ן 103), 232 (2.3
279.0327). 1H NMR, 13C NMR, IR, UV, and MS spec-
tra were almost the same as those of racemic one.
Compound (ם)-1b. 80% ee; m.p. 155–159ЊC;
[␣]D ם140.5 (c 0.50, in CHCl3), [␣]435 ם300.2 (c 0.50,
in CHCl3); CD (cyclohexane)/nm 314 ([h] מ1.4 ן
104) and 234 ([h] ם 1.1 ן 105); m/z (EI) 343.0464
ם
(80Se, M , C18H17NO80Se requires 343.0475). 1H
NMR, 13C NMR, IR, UV, and MS spectra were almost
the same as those of racemic one.
Compound (מ)-1b. 100% ee; m.p. 159–160ЊC;
[␣]D מ165.4 (c 0.19, in CHCl3), [␣]435 מ347.7 (c 0.19,
in CHCl3); CD (cyclohexane)/nm 310 ([h] ם1.0 ן
104) and 234 ([h] מ2.4 ן 105); m/z (EI) 343.0473
ם
(80Se, M , C18H17NO80Se requires 343.0475). 1H
NMR, 13C NMR, IR, UV, and MS spectra were almost
the same as those of racemic one.
ן 104) and 215 (2.7 ן 104) nm; mmax (neat)/cm
מ1
2951, 1452, 1182, 1038, and 830; dH (500 MHz;
CDCl3; Me4Si) 2.17 (3 H, s, SMe), 2.25 (3 H, s, NMe),
2.62 (3 H, s, NMe), 7.04, and 7.09 (4H, ABq, J 8.1,
Ar-H), 7.26 (1 H, d, J 7.6, Ar-H), 7.45 (1 H, dd, J 7.6
and 7.6, Ar-H), 7.74 (1 H, d, J 7.6, Ar-H), 7.78 (1 H,
dd, J 7.6 and 7.6, Ar-H), 8.02 (1 H, d, J 7.6, Ar-H) and
8.72 (1 H, d, J 7.6, Ar-H); dc (125 MHz, CDCl3, Me4Si)
21.2, 42.8, 48.9, 119.6, 125.6, 125.73, 125.75, 126.0,
126.5, 127.5, 129.5, 131.3, 135.4, 138.7, 140.1, 145.6,
Compound (ם)-1c. 90% ee; m.p. 59–62ЊC; [␣]D
ם78.7 (c 0.31, in CHCl3), [␣]435 ם171.3 (c 0.31, in
CHCl3); CD (cyclohexane)/nm 283 ([h] מ2.0 ן 104),
242 ([h] ם1.5 ן 105) and 225 ([h] ם3.9 ן 104); m/z
ם
(EI) 467.1891 (78Se, M , C27H35NO78Se requires
467.1892). 1H NMR, 13C NMR, IR, UV, and MS spec-
tra were almost the same as those of racemic one.
Compound (מ)-1c.
100% ee; m.p. 63–64ЊC;
ם
and 149.9; m/z (EI) 309 (M , 309.1150, C19H19NOS
[␣]D מ87.6 (c 0.58, in CHCl3), [␣]435 מ194.6 (c 0.58,
in CHCl3); CD (cyclohexane)/nm 284 ([h] ם2.7 ן
104), 242 ([h] מ1.9 ן 105) and 224 ([h] מ5.2 ן 104);
requires 309.1187), 292, 187, 168, 154, 127, 105, and
77; [␣]D מ134.7 (c 1.27, in CHCl3), [␣]435 מ220.1 (c
1.27, in CHCl3); CD (cyclohexane)/nm 321 ([h] ם1.4
ן 104), 259 ([h] מ4.6 ן 104), 234 ([h] מ3.4 ן 105)
and 210 ([h] ם2.0 ן 105).
ם
m/z (EI) 469.1858 (80Se, M , C27H35NO80Se
469.1884). 1H NMR, 13C NMR, IR, UV, and MS spec-
tra were almost the same as those of racemic one.
Kinetic Studies on the Racemization of
Optically Active Selenoxides and Telluroxide
Compound (ם)-2b. 100% ee; m.p. 190–191ЊC;
[␣]D ם47.6 (c 0.23, in CHCl3), [␣]435 ם105.6 (c 0.23,
in CHCl3); CD (cyclohexane)/nm 339 ([h] מ1.1 ן
104), 287 ([h] מ1.0 ן 104), 251 ([h] ם4.3 ן 105) and
Kinetic studies on the racemization of optically ac-
tive selenoxides 1a, 1b, and 1c and telluroxide 2b
were examined in solutions (ca. 5 mM) at 26 ע 1ЊC.
The rates of racemization were calculated based on
their specific rotation and plotted according to the
first-order rate equation.
ם
225 ([h] ם4.2 ן 105); m/z (EI) 519.1805 (130Te, M ,
C27H35NO130Te 519.1781). 1H NMR, 13C NMR, IR, UV,
and MS spectra were almost the same as those of the
racemic one.
Compound (מ)-2b. 100% ee; m.p. 189–191ЊC;
[␣]D מ46.0 (c 0.67, in CHCl3), [␣]435 מ104.6 (c 0.67,
in CHCl3); CD (cyclohexane)/nm 341 ([h] ם1.4 ן
104), 290 ([h] ם1.3 ן 104), 252 ([h] מ5.1 ן 105) and
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226 ([h] מ5.0 ן 105); m/z (EI) 519.1803 (130Te, M ,
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and MS spectra were almost same with those of ra-
cemic one.

Thermodynamically Stabilized Chiral Chalcogen Oxides: Optical Resolution and Stereochemistry 237
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[25] All 13C NMR signals corresponding to compound 1c
were observed in C6D6, whereas one signal was not
found in CDCl3.