Generation and characterization of aliphatic selenothioic acid salts

Article abstract of DOI:10.1016/j.tet.2012.06.076

The reaction of thioic acid O-methyl esters with in situ generated aluminum 2-(trimethylsilyl)ethylselenolate gave selenothioic acid Se-(2-trimethylsilyl) ethyl esters in 56-78% yields. The resulting four esters were treated with a THF solution of tetrabutylammonium fluoride (TBAF) to generate selenothioic acid ammonium salts in low to good yields. The efficiency of the generation of the salts depended on the substituents α to the selenocarbonyl group. Fluoride ion in TBAF partly worked as a base to deprotonate from the esters to generate ammonium enethiolates as by-products. Methylation of the acid salts with methyl iodide took place selectively at the selenium atom to give selenothioic acid Se-methyl esters in 48-68% yields. Instead of TBAF, Me₄NF and KF/18-crown-6 were used to generate the salts with other counter cations. The spectroscopic properties of the esters and salts suggested that resonance structures involving carbon-selenium double bonds also contribute to the resonance hybrids of the salts.

Full text of DOI:10.1016/j.tet.2012.06.076

Tetrahedron 68 (2012) 10489e10495
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Generation and characterization of aliphatic selenothioic acid salts
*
Toshiaki Murai , Takamasa Nonoyama
Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 April 2012
Received in revised form 8 June 2012
Accepted 19 June 2012
Available online 28 June 2012
The reaction of thioic acid O-methyl esters with in situ generated aluminum 2-(trimethylsilyl)ethyl-
selenolate gave selenothioic acid Se-(2-trimethylsilyl)ethyl esters in 56e78% yields. The resulting four
esters were treated with a THF solution of tetrabutylammonium fluoride (TBAF) to generate selenothioic
acid ammonium salts in low to good yields. The efficiency of the generation of the salts depended on the
substituents
a to the selenocarbonyl group. Fluoride ion in TBAF partly worked as a base to deprotonate
from the esters to generate ammonium enethiolates as by-products. Methylation of the acid salts with
methyl iodide took place selectively at the selenium atom to give selenothioic acid Se-methyl esters in
48e68% yields. Instead of TBAF, Me4NF and KF/18-crown-6 were used to generate the salts with other
counter cations. The spectroscopic properties of the esters and salts suggested that resonance structures
involving carboneselenium double bonds also contribute to the resonance hybrids of the salts.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Selenothioic acid S-esters
Selenothioic acid Se-esters
Selenothioic acid salts
1. Introduction
O
RC CSeCR'
It is important that we clarify the properties of selenium iso-
logues of dithioic acids1 and their salts2 in organic chemistry be-
cause the replacement of a sulfur atom in organosulfur compounds
with a selenium atom may give rise to compounds with greater
instability and unique properties.3 In fact, dithioic acid, salts and
their esters (RC(S)SR0)4 have been well-known compounds for over
100 years, and their application as metal ligands,5 organocatalysts,6
and key synthetic compounds7 has been intensively continued
even in very recent years. The synthesis of dithioic acid esters has
generally used commercially available carbon disulfide (CS2). In
contrast, a similar approach to selenium isologues is not an easy
way since carbon selenide sulfide (CSeS)8 is highly labile and not
readily available. Although selenium isologues are still of theoret-
ical interest,9 selenothioic acid S-esters and Se-esters had been
ambiguous species10 until Kato and co-workers established several
synthetic methods11 leading to these compounds. For the synthesis
of aliphatic selenothioic acid S-esters, lithium alkyneselenolates 1
generated from terminal alkynes are used as key precursors
(Scheme 1). Their reactions with alkanethiols gave a series of the
corresponding esters 2. Alternatively, acylation of lithium alkyne-
selenolates led to selenoic acid Se-alkynyl esters, and the sub-
sequent addition of thiols under acidic conditions gave the esters 2.
In the former case, the use of silylacetylenes was highly effective,
whereas a range of terminal acetylenes could be used in the latter.
RC CH
R'SH/H+
1) n-BuLi
2) Se
R'SH
Se
RC CSeLi
1
2
R
SR'
Scheme 1. Synthesis of selenothioic acid S-esters 2.
With these methods, a variety of selenothioic acid S-esters 212
were prepared, and new reactions using them were developed.13
For example, in allylation of the ester 2a with excess allyl bro-
mide in the presence of Et3N, three allyl groups were effectively
introduced to the carbon atom
a to the selenocarbonyl group
to give the ester 2b (Scheme 2).14 The further reaction of 2b
with tetrabutylammonium fluoride (Bu4NF, TBAF) led to the first
example of aliphatic selenothioic acid ammonium salt 3a
(Scheme 3).15 Despite the fact that tremendous amounts of exam-
ples of dithioic acid salts have been reported, as their selenium
isologues an inner salt bearing a selenothiocarboxyl group was only
reported around the same time.16 Formation of the salt 3a was
accompanied by the elimination of trimethylsilyl fluoride and
ethylene from 2b. We report here the details of the generation of
aliphatic selenothioic acid salts and their characterization.
* Corresponding author. Tel./fax: þ81 58 293 2614; e-mail address: mtoshi@gi-
fu-u.ac.jp (T. Murai).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.06.076

10490
T. Murai, T. Nonoyama / Tetrahedron 68 (2012) 10489e10495
DIBAL-H
xylene
Se
Br
Et3N
THF
Se
SCH2CH2SiMe3
2a
SR
(Me3SiCH2CH2Se)2
7
0 °C, then
2b
rt, 15 min.
R = CH2CH2SiMe3
S
8
R
OMe
Scheme 2. Triallylation of selenothioic acid S-ester 2a.
i-Bu2AlSeCH2CH2SiMe3
xylene
0 °C, then
+NBu4
Se
Se
SCH2CH2SiMe3
2b
180 °C, 1 or 30 min
-
Bu4NF
THF
S
70%
9a R =
9b
n-C7H15
S
R Se
3a
SiMe3
63%
56%
78%
CH(Ph)Me
cyclohexyl
1-admantyl
Scheme 3. Generation of selenothioic acid salt 3a.
9
9c
9d
2. Results and discussion
Scheme 5. Synthesis of selenothioic acid Se-esters 9.
Initially, enolizable selenothioic acid S-2-(trimethylsilyl)ethyl
esters were subjected to the reaction with TBAF. To confirm the
formation of the desired salt 3a, alkyl halides were added to the
reaction mixture of 3 and TBAF (Scheme 4).
solvent was removed under reduced pressure to give a red oil. The
NMR spectra of the red oil implied the formation of the desired
selenothioic acid salt 3b along with the formation of ammonium
enethiolate 10a as a mixture of E and Z isomers. Nevertheless, the
treatment of the reaction mixture of 9a and TBAF after 3 h with
methyl iodide gave selenothioic acid Se-methyl ester 4b as an iso-
lable product. Although the selectivity of the reaction that leads to
the salt 3b was not high, our idea that the desilylethylation from 9
led to salts 3 worked to some extent.
+NBu4
Se
Bu4NF
THF
Se
-
SCH2CH2SiMe3
S
2a
3
Se
MeI
Bu4NF
THF
SCH2CH2SiMe3
2c
S
Bu4NF
CH3(CH2)5
SiMe3
Se
+NBu4
THF
Se-
SR'
9a
SeMe
SR'
5 89%
S
R
R
R
0 °C, 3 h
SeMe
4a
R
R
R
6
Bu4N+
+NBu4
Se
S
MeI
THF
0 °C
1 h
-
R = CH2CH=CH2
R' = CH2CH2SiMe3
-
+
R'
R'
10a
R' = (CH2)5CH3
SiMe3
S
Se
Scheme 4. Attempts to generate selenothioic acid salts 3.
3b
However, the reaction of the ester 2a with TBAF and alkyl ha-
lides gave complex mixtures. In contrast, the reaction of 2c with
TBAF followed by methylation proceeded smoothly, but did not give
the desired ester 4a. Instead, selenothioketene acetal 5 was ob-
tained in 89% yield. This suggested the formation of ammonium
eneselenolate 6, and the methylation of 6 selectively takes place at
the selenium atom. In this case, Bu4NF acts as a base to deprotonate
S
CH3(CH2)5
SeMe
4b 48%
Scheme 6. Generation of selenothioic acid salt from 9a and its methylation.
the
affinity toward a silicon atom. As starting esters with less acidic
protons, the use of selenothioic Se-2-(trimethylsilyl)ethyl esters 9
was envisioned, since the acidity of -protons is believed to be
a-proton of the ester 2c even if the fluoride ion shows high
a
-
To reduce the deprotonation from the site
a to the thiocarbonyl
group, -disubstituted selenothioic acid Se-esters 9b and 9c were
a,a
a
then used as starting materials (Scheme 7). In the NMR spectra of
the mixture of 9b and TBAF, the signals ascribed to the salt 3c were
observed, but methylation of the reaction mixture mainly gave
selenothioketene acetal 11b as a stereoisomeric mixture along with
a small amount of 4c. Therefore, deprotonation from 9b pre-
reduced on going from C]Se, to C]S, and C]O.
Aliphatic selenothioic acid Se-2-(trimethylsilyl)ethyl esters 9
were prepared by reacting aluminum 2-(trimethylsilyl)ethyl-
selenolate generated in situ from diselenide 717 and DIBALeH with
the corresponding thioic acid O-methyl esters 8 (Scheme 5). In the
reaction at 180 ꢀC for 1 min, the desired products 9ae9c were ob-
tained, whereas a longer reaction time (30 min) was necessary for
the synthesis of Se-ester 9d. These Se-esters 9 are stable under an
atmosphere of inert gas at room temperature.
The generation of selenoic acid salts from esters 9 was then
carried out (Schemes 6, 7, and 9). Ester 9a was treated with a THF
solution of TBAF. The reaction mixture gradually changed from
yellow to red. After the mixture was stirred at 0 ꢀC for 0.5 h, the
dominantly takes place at the position a to thiocarbonyl group of 9b
to generate 10b. The stereochemistry of 11b was determined by
comparing 1H NMR spectra of 11b with those of similar compound
1218 (Scheme 8). The protons of alkyl groups attached to the sulfur
atom oriented at the cis-position of a phenyl group in E-11b and E-
12 were observed at higher regions than those in Z-11b and Z-12.
Similar tendencies were observed for the protons of alkyl groups
attached to the selenium atom. In contrast to the reaction of 9b,
desilylethylation from the ester 9c with TBAF proceeded followed

T. Murai, T. Nonoyama / Tetrahedron 68 (2012) 10489e10495
10491
by the methylation to give ester 4d in 68% yield. The isolation of the
S
Se
- +NBu4
Bu4NF
THF
0 °C
0.5 h
salt 3d as a pure form was not successful since excess TBAF could
not be removed, but NMR spectra showed 3d was formed in good
yield.
SiMe3
R
Se
R
S
9d
88%
3e
S
•
MeI
S
Se
9b
Bu4NF
MeI
THF
0 °C
1 h
R
SeMe
68%
Ph
SiMe3
R =
THF
0 °C, 0.5 h
THF
0 °C, 1 h
4e
S
SMe
SeR
Scheme 9. Generation of selenothioic acid salt from 9d and its methylation.
Ph
Ph
11b
+
SeMe
precipitates were filtered through a glass filter, and the reaction
mixture was concentrated. To the residue was added Et2O, and the
filtration of the solution gave the corresponding salts 12 and 13 as
deep green and gray solids, respectively.
4c
52%
4c : E-11b : Z-11b = 3 : 47 : 50
Bu4N+
+NBu4
Se
S
-
Ph
-
Ph
S
SeR
10b
+NMe4
88%
Me4NF
S
Se
3c
-
SiMe3
CH3CN
R
Se
R
12
S
rt, 3 h
9d
S
Se
9c
+NBu4
Se
-
Bu4NF
THF
0 °C
0.5 h
SiMe3
S
•
M+
S
26%
KF
Se
R
13
3d
-
18-crown-6
CH3CN
R =
S
MeI
THF
0 °C
1 h
82 °C, 3 h
SeMe
4d
M+ = K+ 18-crown-6
68%
Scheme 10. Generation of selenothioic acid salts 12 and 13 from 9d.
Scheme 7. Generation of selenothioic acid salts from 9b and 9c and their methylation.
The spectroscopic properties of some esters and salts are sum-
marized in Table 1. As observed for aromatic selenothioic acid esters
and salts, in 77Se and 13C NMR spectra, the signals due to esters 9c
and 9d were observed at ca. 830 ppm, i.e., at higher fields than
those due to salts 3d and 3e. These values are larger than those of
selenoic acid O-esters and selenoamides, which clearly possess
carboneselenium double bonds in the compounds.3c,19 The cou-
pling constants between the carbon and selenium bonds of salts 3
were greater than those of esters 9. In the UV/vis spectra, the lon-
gest wavelengths of salts 3 were red-shifted compared to those of
esters 9. These results suggested resonance structures involving
seleniumecarbon double bonds also contribute to the resonance
hybrids of salts 3.
2.62
2.33
SCH2Pr
SeCH3
SCH3
SeCH2CH2SiMe3
2.85
Ph
Ph
Ph
H
E-12
2.13
E-11b
2.63
SeCH2CH2SiMe3
SCH3
2.10
SeCH3
SCH2Pr
2.68
Ph
H
2.37
Z-12
Z-11b
Table 1
Spectroscopic properties of esters 9 and salts 3
Scheme 8. Chemical shifts of selenothioketene acetals 11b and 12 in 1H NMR spectra.
1JC]Se (Hz)
UV/visb lmax (nm)
a
Compd
d
77Se NMRa
13C NMRa
Adamantanecarboselenothioic acid Se-ester 9d was used as an
example of trisubstituted esters (Scheme 9). The crude products
were washed with hexane several times, and concentrated in vacuo
to form the desired salt 3e as a red-brown oil. The NMR spectra of
the salt showed that it was formed in a pure form, although they
were slightly contaminated with unreacted TBAF. Methylation of
the salt 3e also took place selectively at the selenium atom to give
selenothioic acid Se-ester 4e in good yields.
9c
9d
3d
3e
836.6
827.8
1090.7
1064.0
252.0
258.9
273.4
279.6
168.5
172.3
dc
477
486
522
575
209.2
a
CDCl3 was used for 9 and THF-d8 was used for 3.
THF was used as a solvent.
b
c
Not determined.
Finally, the generation of selenothioic acid salts with other
counter cations was examined (Scheme 10). Instead of a THF so-
lution of TBAF, Me4NF and KF were used in CH3CN. In the latter case,
18-crown-6 was also used as an additive. The reactions proceeded
smoothly, and the starting ester 9d was consumed within 3 h. The
Additionally, selenothioketene acetal 11b was used as a pre-
cursor of selenothioic acid S-ester 2d (Scheme 11). The reaction of
11b with TBAF went to completion within 1 h, and aqueous workup
of the reaction mixture gave 2d as a stable purple oil in good yield.

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T. Murai, T. Nonoyama / Tetrahedron 68 (2012) 10489e10495
4.2. Synthetic procedure of selenothioacetic acid S-(2-
trimethylsilyl)ethyl ester (2a)
Bu4NF
SMe
Se
Ph
SiMe3
THF
0 °C, 1 h
In a 300 mL three-necked flask, BuLi (12.8 mL, 20.0 mmol) was
added to an Et2O (200 mL) solution of (trimethylsilyl)acetylene
(2.8 mL, 20.0 mmol) at 0 ꢀC. After the stirring at 0 ꢀC for 10 min,
powder selenium (1.58 g, 20.0 mmol) was added to the resulting
mixture at 20 ꢀC, and it was stirred for 20 min. To this was added 2-
(trimethylsilyl)ethanethiol (3.2 mL 20.0 mmol) at 0 ꢀC, and the
mixture was stirred for 30 min. The reaction mixture was poured
into water, and extracted with Et2O. The organic layer was dried
over MgSO4 and concentrated in vacuo. The residue was purified by
column chromatography on silica gel using hexane as an eluent to
give 2.68 g of 2a (56%) as a purple oil; IR (neat) 2953, 2902, 1654,
11b
+NBu4
Se–
14
SMe
Se
H2O
Ph
Ph
SMe
2d
65%
Scheme 11. Conversion of 11b to selenothioic acid ester 2d.
3. Conclusion
1560, 1418, 1357, 1249, 1166, 1136, 1107, 1009, 1008, 824 cmꢁ1 1H
;
NMR (CDCl3)
d 0.06 (s, 9H, SiMe3), 1.00 (m, 2H, CH2Si), 2.55 (s, 3H,
In summary, the generation and characterization of aliphatic
selenothioic acid salts were described. As precursors of the salts,
selenothioic acid Se-(2-trimethylsilyl)ethyl esters were prepared by
the reaction of thioic acid O-methyl esters with aluminum 2-(tri-
methylsilyl)ethylselenolate. Treatment of the esters with TBAF
could lead to the salts. Deprotonation from the esters competitively
CH3), 3.20 (m, 2H, SCH2); 13C NMR (CDCl3)
d
ꢁ1.8, 14.4, 44.9, 38.2
(SCH2), 44.9 (CH3), 237.8 (C]Se, JCeSe¼222.3 Hz); 77Se NMR
1
(CDCl3, Me2Se)
d 1501.9; MS (EI) m/z 240. Anal. Calcd for
C7H16SSeSi; C, 35.13; H, 6.74. Found: C, 35.35; H, 7.03.
4.3. Synthetic procedure for 2-(2-propenyl)-4-
took place depending on the substituents
a
to the thiocarbonyl
penteneselenothioic acid S-2-(trimethylsilyl)ethyl ester (2c)
group. Methylation of the salts occurred selectively at the selenium
atom of the salts to give selenothioic acid Se-esters with high effi-
ciency. The spectroscopic properties of the salts suggested that
carboneselenium bonds have a double-bond character.
In a 50 mL three-necked flask, to a solution of ester 2a (0.723 g,
3.0 mmol) and 3-bromo-1-propene (0.51 mL, 5.9 mmol) in 20 mL of
THF was added Et3N (0.84 mL, 0.59 mmol) at 0 ꢀC. The reaction
mixture was stirred at 0 ꢀC for 2 h. The reaction mixture was poured
into water, and extracted with Et2O. The organic layer was dried over
MgSO4 and concentrated in vacuo. The residue was purified by
column chromatography on silica gel using hexane as an eluent to
give 0.43 g of 2c (56%) as a purple oil; IR (neat) 3077, 2953, 2904,
4. Experimental section
4.1. General information
Characterization: Melting points were measured by a Yanagi-
moto micromelting point apparatus (uncorrected). The IR spectra
were obtained on a PERKIN ELMER FT-IR 1640 and JASCO FT/IR 410
spectrophotometers. The 1H NMR spectra were measured on
1641, 1560, 1508, 1438, 1250, 1165, 1007, 916, 858 cmꢁ1
;
1H NMR
(CDCl3)
d
0.06 (s, 9H, SiMe3), 0.98 (m, 2H, CH2Si), 2.39 (ddd, J¼5.9, 7.1,
13.4 Hz, 2H, CH2), 2.61 (ddd, J¼7.0, 8.2,15.1 Hz, 2H, CH2), 3.22 (m, 2H,
SCH2), 3.37 (tt, J¼5.8, 8.4 Hz, 1H, CH), 4.96e5.04 (m, 4H, CH2), 5.71
a
JEOL
a
-400 (399.7 MHz) in CDCl3, THF-d8, and DMSO-d6.
(ddt, J¼7.01,10.2,17.1 Hz, 2H, CH); 13C NMR (CDCl3)
d
ꢁ1.7,14.3, 36.2,
1
Chemical shifts of protons are reported in
d
values referred to
41.1, 64.2, 116.9, 135.3, 248.0 (C]Se, JCeSe¼224.3 Hz); 77Se NMR
tetramethylsilane as an internal standard. The 13C (100.4 MHz)
NMR spectra and the 77Se (76.2 MHz) NMR spectra were measured
(CDCl3, Me2Se) d 1423.9; MS (EI) m/z 320. Anal. Calcd for
C13H24SSeSi; C, 48.88; H, 7.57. Found: C, 48.63; H, 7.47.
on the spectrometer JEOL
expressed in values deshielded with respect to Me2Se as an
a
-400. The 77Se chemical shifts are
d
4.4. Reaction of ester 2c with TBAF and methyl iodide leading
to selenothioketene acetal 5
external standard. UV/vis spectra were measured on a JASCO U
best 55 or HITACHI U-4000. The mass spectra (MS) were taken on
SHIMADZU GCMS QP1000 (EI mode) and GCMS 9020DF high
resolution mass spectrometers. The high resolution mass spec-
troscopy (HRMS) was taken on JEOL JMS-GCmate II GCMS SYSTEM.
Elemental analyses were carried out by Elemental Analysis Center
of Kyoto University.
Materials: Diethyl ether (Et2O) and tetrahydrofuran (THF) were
distilled from sodium/benzophenone ketyl prior to use. Acetoni-
trile and dichloromethane (CH2Cl2) were distilled from phos-
phorus pentoxide. Xylene was distilled from calcium hydride.
Anhydrous tetramethylammonium fluoride20 was obtained from
the tetramethylammonium fluoride tetrahydrate by removal of
the water under reduced pressure (150 ꢀC/1.0 mmHg) with stir-
ring for about 1 h. Xylene, methyl iodide, and potassium fluoride
were purchased from Nacalai Tesque, Inc., and used without
further purification. 18-Crown-6 ether, tetrabutylammonium
fluoride (in THF), and tetramethylammonium fluoride tetrahy-
drate were purchased from Aldrich Chemical Company, Inc., and
used without further purification. Diisobutylaluminum hydride
(DIBALeH) 1.0 M hexane solution was purchased from Kanto
Chemical Co., Inc. and used without further purification. Silica gel
used in column chromatography was silica gel 60N from Kanto
Chemical Co., Inc.
In a 20 mL two-necked flask, tetrabutylammonium fluoride
(0.3 mL, 0.3 mmol) was added to a THF (5 mL) solution of ester 2c
(0.096 g, 0. 3 mmol) at 0 ꢀC. After stirring at 0 ꢀC for 3 h, methyl
iodide (0.05 mL, 0.8 mmol) was added at 0 ꢀC, and the stirring was
continued for 1 h. The reaction mixture was poured into water, and
extracted with Et2O. The organic layer was dried over MgSO4 and
concentrated in vacuo. The residue was purified by column chro-
matography on silica gel using hexane as an eluent to give 0.098 g
of 5 (89%) as a yellow oil; IR 3079, 2954, 2897, 1637, 1425, 1380,
1249, 1161, 1081, 993, 941, 912, 861 cmꢁ1 1H NMR
; d 0.00 (s, 9H,
SiMe3), 0.80 (m, 2H, CH2), 2.15 (s, 3H, SeMe), 2.69 (m, 2H, CH2), 3.20
(dt, J¼1.5, 6.3 Hz, 2H, CH2), 3.25 (dt, J¼1.5, 6.6 Hz, 2H), 5.01 (m, 4H,
CH2), 5.71 (m, 2H, CH); 13C NMR
d
ꢁ1.7, 8.1, 17.5, 31.2, 39.7, 41.3,
115.9, 124.5, 135.3, 135.5, 147.4; 77Se NMR (CDCl3, Me2Se)
d 170.5;
MS (EI) m/z 334; HRMS calcd for C14H26SSeSi (Mþ): 334.0690,
found: 334.0701.
4.5. General procedure for the synthesis of selenothioic acid
Se-(2-trimethylsilyl)ethyl esters 9
In a 20 mL two-necked round-bottom flask, a xylene solution of
1.0 M DIBALeH in hexane (2.5 mL, 2.5 mmol) was added to a xylene

T. Murai, T. Nonoyama / Tetrahedron 68 (2012) 10489e10495
10493
solution (2 mL) of diselenide 7 (0.360 g, 1.00 mmol) at 0 ꢀC, and the
mixture was stirred at 25 ꢀC for 15 min. A xylene solution (2 mL) of
thioic acid O-methyl ester 8 (4.00 mmol) was added to the resulting
mixture at 0 ꢀC, and the mixture was heated at 180 ꢀC. The reaction
mixture was poured onto ice/water mixture, and extracted with
Et2O. The organic layer was dried over MgSO4 and concentrated in
vacuo. The residue was purified by column chromatography on
silica gel using hexane as an eluent to give 9 as a yellow oil.
and extracted with CH2Cl2. The organic layer was collected, dried
over MgSO4, and concentrated to give crude products, which were
purified by column chromatography on silica gel to give the cor-
responding methylated products 4 and/or 11.
4.6.1. Tetrabutylammonium octaneselenothioate (3b). 1H NMR
(THF-d8)
d
0.88 (t, J¼7.5 Hz, 3H, CH3), 0.98 (t, J¼7.3 Hz, 12H, CH3),
1.29e1.39 (m, 8H, CH2), 1.42 (sex, J¼7.3 Hz, 8H, CH2), 1.74 (br, 8H,
CH2), 3.52 (br, 8H, CH2), the protons (CH2CSSe) were not identified;
4.5.1. Octaneselenothioic acid Se-2-(trimethylsilyl)ethyl ester (9a). A
yellow oil; IR (neat) 2925, 2855, 1794, 1719, 1460, 1401, 1249,
13C NMR (THF-d8):
d 1114.2.
d
267.1 (C]Se); 77Se NMR (THF-d8, Me2Se):
869 cmꢁ1
;
1H NMR (CDCl3)
d
0.05 (s, 9H, SiMe3), 0.86 (t, J¼6.8 Hz,
3H, CH3), 0.99e1.04 (m, 2H, CH2Si), 1.26e1.32 (m, 8H, CH2), 1.80
(quint, J¼7.3 Hz, 2H, CH2), 3.02 (t, J¼7.6 Hz, 2H, CH2), 3.20e3.25 (m,
4.6.2. Octaneselenothioic acid Se-methyl ester (4b). A yellow oil; IR
(neat) 3423, 3068, 2925, 1794, 1723, 1598, 1579, 1385, 1145, 963,
2H, SeCH2); 13C NMR (CDCl3)
d
ꢁ1.79, 14.1, 16.4, 22.6, 28.8, 29.0,
876 cmꢁ1
;
1H NMR (CDCl3)
d
0.86 (t, J¼6.8 Hz, 3H, CH3), 1.26e1.41
29.3, 31.4, 31.7, 55.6, 246.0 (C]S: JCeSe¼166.7 Hz); 77Se NMR
(m, 8H, CH2), 1.82 (quint, J¼7.6 Hz, 2H, CH2), 2.53 (s, 3H, SeCH3),
1
(CDCl3, Me2Se)
d
851.4; UV/vis (THF) lmax (log
3 ) 476 (1.51), 339
3.06 (t, J¼7.8 Hz, 2H, CH2); 13C NMR (CDCl3)
d 13.7, 14.1, 22.6, 28.7,
(4.24), 269 (4.10), 221 (4.49) nm; MS (EI) m/z 323 (Mþ); HRMS Calcd
29.0, 31.4, 31.7, 55.1, 245.3 (C]S: JCeSe¼162.8 Hz); 77Se NMR
1
for C13H28SSeSi: (Mþ) 324.0846, Found: 324.0824.
(CDCl3, Me2Se)
d
721.6; UV/vis (THF) lmax (log ) 469 (1.47), 330
3
(4.11), 270 (4.26), 220 (4.47) nm; HRMS calcd for C9H18SSe: (Mþ)
238.0294, found: 238.0281.
4.5.2. dl-2-Phenylpropaneselenothioic acid Se-2-(trimethylsilyl)ethyl
ester (9b). An orange oil; IR (neat) 3027, 2953, 2925, 1600, 1493,
1451, 1248, 861, 697 cmꢁ1
;
1H NMR (CDCl3)
d
0.04 (s, 9H, SiMe3),
4.6.3. Tetrabutylammonium phenylpropaneselenothioate (3c). 1H
0.94e0.99 (m, 2H, CH2Si), 1.70 (d, J¼6.8 Hz, 3H, CH3), 3.16e3.21 (m,
2H, SeCH2), 4.58 (q, J¼7.2 Hz, 1H, CH), 7.24 (t, J¼6.3 Hz, 1H, Ar), 7.31
(t, J¼7.1 Hz, 2H, Ar), 7.40 (d, J¼6.8 Hz, 2H, Ar); 13C NMR (CDCl3)
NMR (THF-d8)
d
0.96 (t, J¼7.3 Hz, 12H, CH3), 1.37 (sex, J¼7.3 Hz, 8H,
CH2), 1.55 (d, J¼6.8 Hz, 3H, CH3), 1.65 (br, 8H, CH2), 3.33 (br, 8H,
CH2), 5.04 (q, J¼7.2 Hz, 1H, CH), 7.03e7.15 (m, 1H, Ar), 7.63 (t,
d
ꢁ1.82, 16.0, 22.4, 29.1, 62.8, 127.2, 127.8, 128.5, 142.0, 248.9 (C]S:
J¼7.3 Hz, 2H, Ar), 8.28 (d, J¼7.8 Hz, 2H, Ar); 13C NMR (THF-d8)
d 14.2,
1JCeSe¼169.9 Hz); 77Se NMR (CDCl3, Me2Se)
d
848.5; UV/vis (THF)
20.6, 24.4, 24.9, 59.2, 73.0, 125.7, 127.7, 128.5, 146.6 (Ar), 268.4 (C]
lmax (log
3
) 480 (1.77), 341 (4.18), 227 (4.65) nm; MS (EI) m/z 329
Se: 1JCeSe¼205.6 Hz); 77Se NMR (THF-d8, Me2Se)
d 1144.7.
(Mþ). Anal. Calcd for C14H22SSeSi: C, 51.04; H, 6.73. Found: C, 50.97;
H, 6.61.
4.6.4. Tetrabutylammonium E-1-(2-trimethylsilylethylseleno)-2-
phenyl-1-propenethiolate (E-10b). 1H NMR (THF-d8)
0.05 (s, 9H,
d
4.5.3. Cyclohexanecarboselenothioic acid Se-2-(trimethylsilyl)ethyl
SiMe3), 0.96 (t, J¼7.3 Hz, 12H, CH3), 1.37 (sex, J¼7.3 Hz, 8H, CH2),
1.65 (br, 8H, CH2), 2.14 (s, 3H, CH3), 3.16e3.21 (m, 2H, SeCH2), 3.33
(br, 8H, CH2), 7.03e7.15 (m, 1H, Ar), 7.63 (t, J¼7.3 Hz, 2H, Ar), 8.28 (d,
ester (9c). A yellow oil; IR (neat) 2930, 2853, 1447, 1248, 1185, 927,
; d 0.05 (s, 9H, SiMe3),
860, 782, 695 cmꢁ1 1H NMR (CDCl3)
0.98e1.03 (m, 2H, CH2Si), 1.15e1.38 (m, 3H, cyclohexyl), 1.59e1.73
(m, 3H, cyclohexyl), 1.78e1.82 (m, 2H, cyclohexyl), 1.90e1.94 (m,
2H, cyclohexyl), 3.12e3.24 (m, 3H, cyclohexyl, SeCH2); 13C NMR
J¼7.8 Hz, 2H, Ar); 13C NMR (THF-d8)
d 2.0, 14.2, 20.6, 21.4, 22.9, 24.9,
30.7, 59.2, 124.8, 125.7, 127.7, 128.5 (Ar), 141.2, 146.6; 77Se NMR
(THF-d8, Me2Se)
d 462.5.
(CDCl3)
d
ꢁ1.78, 16.3, 25.7, 26.1, 28.2, 34.7, 63.4, 252.0 (C]S:
1JCeSe¼168.5 Hz); 77Se NMR (CDCl3, Me2Se)
d
836.6; UV/vis (THF)
4.6.5. Tetrabutylammonium Z-1-(2-trimethylsilylethylseleno)-2-
phenyl-1-propenethioalte (Z-10b). 1H NMR (THF-d8)
lmax (log
3
) 477 (1.37), 338 (4.18), 274 (4.41), 221 (4.47) nm; MS (EI)
d
ꢁ0.01 (s,
m/z 307 (Mþ) 127 (MþꢁSeCH2CH2SiMe3); HRMS calcd for
9H, SiMe3), 0.96 (t, J¼7.3 Hz, 12H, CH3), 1.37 (sex, J¼7.3 Hz, 8H, CH2),
1.65 (br, 8H, CH2), 2.34 (s, 3H, CH3), 3.00e3.04 (m, 2H, SeCH2), 3.33
(br, 8H, CH2), 7.03e7.15 (m, 1H, Ar), 7.63 (t, J¼7.3 Hz, 2H, Ar), 8.28 (d,
C12H24SSeSi: (Mþ) 308.0533, found: 308.0530.
4.5.4. Adamantanecarboselenothioic acid Se-2-(trimethylsilyl)ethyl
J¼7.8 Hz, 2H, Ar); 13C NMR (THF-d8)
d 2.0, 14.2, 20.6, 20.8, 24.9, 30.5,
ester (9d). An orange solid; mp 72e74 ꢀC; IR (KBr) 2901, 2847, 1448,
30.9, 59.2, 124.6, 125.7, 127.7, 128.5, 140.6, 146.6; 77Se NMR (THF-d8,
1342, 1246, 1150, 1051, 1035, 858, 836 cmꢁ1; 1H NMR (CDCl3)
d
0.05
Me2Se)
d 438.8.
(s, 9H, SiMe3), 0.96e1.01 (m, 2H, CH2Si), 1.68e2.12 (m, 15H, Ad),
3.15e3.20 (m, 2H, SeCH2); 13C NMR (CDCl3)
d
ꢁ1.75, 15.8, 28.2, 29.1,
4.6.6. Phenylpropaneselenothioic acid Se-methyl ester (4c). 1H NMR
1
36.6, 44.1, 56.9, 258.9 (C]S: JCeSe¼172.3 Hz); 77Se NMR (CDCl3,
(CDCl3)
d
1.73 (d, J¼6.8 Hz, 3H, CH3), 2.47 (s, 3H, SeCH3), 4.59 (q,
Me2Se)
d
827.8; UV/vis (THF) lmax (log
3
) 486 (1.56), 340 (4.09), 274
J¼7.1 Hz, 1H, CH), 7.23e7.41 (m, 5H, Ar); 13C NMR (CDCl3)
d 13.5,
(4.52), 231 (4.45) nm; MS (EI) m/z 359 (Mþ). Anal. Calcd for
22.6, 62.5, 125.5, 127.4, 127.5, 141.9, 248.9; 77Se NMR (CDCl3, Me2Se)
C16H28SSeSi: C, 53.45; H, 7.85. Found: C, 53.52; H, 8.03.
d 720.7.
4.6. General procedure for the reaction of selenothioic acid
Se-2-(trimethylsilyl)ethyl esters 9 with tetrabutylammonium
fluoride and the methylation of the resulting solution
4.6.7. (E)-1-(Methylthio)-1-(trimethylsilylethylseleno)-2-
phenylpropene (E-11b). IR (neat) 2952, 2917, 1599, 1489, 1439, 1418,
1366, 1248, 1148, 1074, 1027, 1011, 859, 757, 697 cmꢁ1 1H NMR
;
(CDCl3)
SCH3), 2.33 (s, 3H, CH3), 2.87e2.92 (m, 2H, SeCH2), 7.13e7.36 (m,
5H, Ar); 13C NMR (CDCl3)
ꢁ1.78, 18.7, 19.1, 23.4, 24.7, 124.8, 126.3,
d 0.05 (s, 9H, SiMe3), 1.01e1.06 (m, 2H, CH2Si), 2.12 (s, 3H
In a 20 mL two-necked flask, tetrabutylammonium fluoride
(0.2 mL, 0.2 mmol) was added to a THF solution of selenothioic acid
Se-2-(trimethylsilyl)ethyl esters 9 (0.2 mmol) at 0 ꢀC. After being
stirred at 0 ꢀC for an appropriate time, the reaction mixture was
concentrated to give selenothioic acid salts 3 and/or enethiolates
10. For methylation of the salts 3 and/or 10, the methyl iodide was
added to the reaction mixture of 9 and Bu4NF, and the mixture was
stirred at 0 ꢀC for 1 h. The reaction mixture was poured into water,
d
127.9, 128.0, 144.9, 147.3; 77Se NMR (CDCl3, Me2Se)
d 331.7; MS (EI)
m/z 343 (Mþ); HRMS calcd for C15H24SSeSi: (Mþ) 344.05332, found:
344.05496.
4.6.8. (Z)-1-(Methylthio)-1-(trimethylsilylethylseleno)-2-
phenylpropene (11b). IR (neat) 2952, 2917, 1599, 1489, 1439, 1418,

10494
T. Murai, T. Nonoyama / Tetrahedron 68 (2012) 10489e10495
1366, 1248, 1148, 1074, 1027, 1011, 859, 757, 697 cmꢁ1
(CDCl3)
ꢁ0.04 (s, 9H, SiMe3), 0.79e0.84 (m, 2H, CH2Si), 2.35 (s, 3H,
CH3), 2.37 (s, 3H SCH3), 2.60e2.65 (m, 2H, SeCH2), 7.13e7.36 (m, 5H,
Ar); 13C NMR (CDCl3)
ꢁ1.88, 18.2, 19.7, 23.3, 27.1, 124.2, 126.9,
;
1H NMR
4.8. Synthetic procedure for potassium
adamantaneselenothioate 18-crown-6 ether complex (13)
d
d
In a 20 mL two-necked flask, a solution of adamantane
127.8, 128.0 (Ar), 144.0, 147.2; 77Se NMR (CDCl3, Me2Se)
d
312.8; MS
carboselenothioic acid Se-2-(trimethylsilyl)ethyl ester 9d (0.302 g,
0.804 mmol) in CH3CN (10 mL) was added to a suspension of po-
tassium fluoride (0.073 g,1.26 mmol) and 18-crown-6 ether (0.222 g,
0.840 mmol) in the same solvent (2 mL) at 20 ꢀC. The mixture was
heated at 82 ꢀC for 3 h. The insoluble parts were filtered out. The
solvent was evaporated under reduced pressure. To the residue was
added Et2O (7 mL) at 20 ꢀC, followed by stirring for 10 min. Filtration
of theresultingprecipitates gave0.150 g (26%)of13 asa graysolid; 1H
(EI) m/z 343 (Mþ); HRMS calcd for C15H24SSeSi: (Mþ) 344.05332,
found: 344.05496.
4.6.9. Tetrabutylammonium cyclohexanecarboselenothioate (3d). A
red oil; IR (neat) 2959, 2930, 2873, 2044, 1834, 1463, 1384, 1232,
1147, 1110, 1065, 1032, 935, 885, 862 cmꢁ1; 1H NMR (THF-d8)
d 0.99
(t, J¼7.6 Hz, 12H, CH3), 1.12e1.22, 1.28e1.33, 1.59e1.62, 1.85e1.89
(m, 10H, cyclohexyl), 1.43 (sex, J¼7.6 Hz, 8H, CH2), 1.73 (m, 8H, CH2),
NMR (DMSO-d6)
13C NMR (DMSO-d6)
271.9 (C]Se); 77Se NMR (DMSO-d6)
d
1.53e2.06 (m,15H, Ad), 3.54 (s, 24H,18-Crown-6);
28.4, 36.7, 44.4, 53.4 (Ad), 69.4 (18-Crown-6),
1334.1.
3.37e3.51 (m, 9H, CH2, cyclohexyl); 13C NMR (THF-d8)
d
14.2, 20.7,
d
25.0, 27.4, 27.6, 36.2, 59.5, 67.9, 273.4 (C]Se); 77Se NMR (THF-d8,
Me2Se) 1090.7; UV/vis (THF) lmax (log ) 522 (2.26), 340 (3.18),
305 (3.22), 224 (3.65) nm.
d
d
3
4.9. Synthetic procedure for phenylpropaneselenothioic acid
S-methyl ester (2d)
4.6.10. Cyclohexanecarboselenothioic acid Se-methyl ester (4d). A
yellow oil; IR (neat) 2925, 2852, 1447, 1241, 1188, 1035, 926 cmꢁ1
1H NMR (CDCl3)
1.16e1.41 (m, 2H, cyclohexyl), 1.65e1.75 (m, 2H,
;
In a 20 mL two-necked flask, tetrabutylammonium fluoride
(0.5 mL, 0.5 mmol) was added to a THF solution (3 mL) of ketene
selenothioacetal 11b (0.171 g, 0.50 mmol) at 0 ꢀC. It was stirred at
that temperature for 1 h. The reaction mixture was poured into
water, and extracted with Et2O. The organic layer was dried over
MgSO4 and concentrated in vacuo. The residue was purified by
column chromatography on silica gel using hexane (Rf¼0.02) as an
eluent to give 0.079 g (65%) of 2d as a purple oil: IR (neat) 3069,
3025, 2971, 1599, 1492, 1450, 1412, 1369, 1128, 1016, 903, 763,
d
cyclohexyl), 1.78e1.83 (m, 3H, cyclohexyl), 1.92e1.96 (m, 3H,
cyclohexyl), 2.50 (s, 3H, SeCH3), 3.21 (tt, J¼3.4, 11.5 Hz, 1H, cyclo-
hexyl); 13C NMR (CDCl3)
d 12.7, 25.6, 26.1, 34.8, 63.4, 251.3 (C]S:
1JCeSe¼164.2 Hz); 77Se NMR (CDCl3, Me2Se)
d 707.0; UV/vis (THF)
lmax (log ) 475 (1.53), 331 (3.99), 271 (4.01), 218 (4.42) nm; MS (EI)
3
m/z 221 (Mþ); HRMS calcd for C8H14SSe: (Mþ) 221.9981, found:
221.9961.
696 cmꢁ1; 1H NMR (CDCl3)
d
1.79 (d, J¼7.3 Hz, 3H, CH3), 2.59 (s, 3H,
SCH3), 4.65 (q, J¼7.0 Hz, 1H, CH), 7.14e7.46 (m, 5H, Ar); 13C NMR
4.6.11. Tetrabutylammonium adamantanecarboselenothioate (3e). A
red-brown oil; IR (neat) 2959, 2042, 1834, 1471, 1384, 1233, 1152,
(CDCl3)
d 23.1, 24.1, 63.9, 127.2, 127.6, 128.4, 141.4, 249.0 (C]Se:
1110,1005, 893, 804, 739 cmꢁ1; 1H NMR (THF-d8)
d
0.99 (t, J¼7.3 Hz,
1JCeSe¼224.7 Hz); 77Se NMR (CDCl3, Me2Se)
d 1509.5; UV/vis (THF)
12H, CH3), 1.43 (sex, J¼7.3 Hz, 8H, CH2), 1.62e1.68, 1.70e1.78 (m,
lmax (log ) 562 (1.81), 272 (3.62), 242 (3.83), 220 (4.37) nm; MS (EI)
3
m/z 243 (Mþ); HRMS calcd for C10H18SSe: (Mþ) 243.9825, found:
14H, Ad, CH2), 1.96 (br, 2H, Ad), 2.26 (d, J¼2.9 Hz, 7H, Ad), 3.46 (t,
J¼7.3 Hz, 8H, CH2); 13C NMR (THF-d8)
d 14.2, 20.7, 24.9, 31.2, 38.3,
243.9813.
46.4, 58.3, 59.3, 279.6 (C]Se: 1JCeSe¼209.2 Hz); 77Se NMR (THF-d8,
Me2Se)
d
1064.0; UV/vis (THF) lmax (log ) 575 (1.58), 295 (3.61),
3
Acknowledgements
254 (3.52), 220 (3.93) nm.
This work was supported by the Collaborative Research Program
of Institute for Chemical Research, Kyoto University (grant #
2012-10).
4.6.12. Adamantaneselenothioic acid Se-methyl ester (4e). A yellow
solid; mp 70e76 ꢀC; IR (KBr) 2902, 2844, 1637, 1447, 1401, 1341,
1259, 1186, 1050, 1037, 907, 833, 737 cmꢁ1 1H NMR (CDCl3)
;
d
1.69e1.76, 2.08e2.14 (m, 15H, Ad), 2.46 (s, 3H, SeCH3); 13C NMR
References and notes
(THF-d8)
d 12.9 (SeCH3), 29.0, 36.5, 44.2, 56.9 (Ad), 258.2 (C]S:
1JCeSe¼168.1 Hz); 77Se NMR (CDCl3, Me2Se)
d 703.6; UV/vis (THF)
1. Niyomura, O.; Kato, S. In Topics in Current Chemistry; Kato, S., Ed.; Springer:
Berlin, 2005; Vol. 251, p 1.
2. Kano, N.; Kawashima, T. In Topics in Current Chemistry; Kato, S., Ed.; Springer:
Berlin, 2005; Vol. 251, p 141.
lmax(log ) 483 (1.58), 336 (4.15), 239 (3.82), 226 (4.44) nm; MS (EI)
3
m/z 273 (Mþ). Anal. Calcd for C12H18SSe: C, 52.74; H, 6.64. Found: C,
52.79; H, 6.44.
3. For recent reviews of organoselenium chemistry, see: (a) Handbook of Chalco-
gen Chemistry; Devillanova, F. A., Ed.; RSC: Cambridge, 2007; (b) Selenium and
Tellurium Chemistry; Woolins, J. D., Laitinen, R. S., Eds.; Springer: Berlin, 2011;
(c) Organoselenium Chemistry; Wirth, T., Ed.; Wiley-VCH: Weinheim, 2012.
4. For recent reviews, see: (a) Glass, R. S. In Science of Synthesis; Charette, A., Ed.;
Thieme: Stuttgart, 2005; Vol. 22, p 109; (b) Ishii, A.; Nakayama, J. In Topics in
Current Chemistry; Kato, S., Ed.; Springer: Berlin, 2005; Vol. 251, p 181.
5. (a) Naeem, S.; Thompson, A. L.; Delaude, L.; Wilton-Ely, J. D. E. T. Chem.dEur. J.
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Wilton-Dly, D. E. T. Dalton Trans. 2011, 40, 3737; (c) Marchetti, F.; Zacchini, S.;
Salmi, M.; Busetto, L.; Zanotti, V. Eur. J. Inorg. Chem. 2011, 1260; (d) Siemeling,
4.7. Synthetic procedure for tetramethylammonium
adamantaneselenothioate (12)
In a 20 mL two-necked flask, adamantanecarboselenothioic acid
Se-2-(trimethylsilyl)ethyl ester (9d) (0.441 g, 1.23 mmol) was
added to a CH3CN (3 mL) suspension of tetramethylammonium
fluoride (0.255 g, 2.74 mmol) at 20 ꢀC. After stirring at 20 ꢀC for 3 h,
the reaction mixture was filtered through a glass filter (G4) to
separate the insoluble parts, and the solvent was removed under
reduced pressure. To this was added Et2O (5 mL) and at 20 ꢀC, the
mixture was stirred for 5 min. Filtration of the resulting deposits
gave 0.334 g (82%) of 12 as a deep green solid; mp: 206e212 ꢀC
(decomp.); IR (KBr) 3013, 2902, 2844, 2103, 1524, 1488, 1404, 1256,
€
U.; Memczak, H.; Bruhn, C.; Vogel, F.; Trager, F.; Baio, J. E.; Weidner, T. Dalton
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Richter, J. D.; Thomas, A. A. Angew. Chem., Int. Ed. 2012, 51, 2681.
6. Hans, M.; Wouters, J.; Demonceau, A.; Delaude, L. Eur. J. Org. Chem. 2011, 7083.
7. (a) Wang, X.-N.; Shen, L.-T.; Ye, S. Chem. Commun. 2011, 8388; (b) Busetto, L.;
Marchetti, F.; Zacchini, S.; Zanotti, V. J. Organomet. Chem. 2011, 696, 4051; (c)
€
€
Dobele, M.; Wiehn, M. S.; Brase, S. Angew. Chem., Int. Ed. 2011, 50,11533; (d) Nandi,
G. C.; Samai, S.; Singh, M. S. J. Org. Chem. 2011, 76, 8009; (e) Amareshwar, V.;
1004, 949, 896 cmꢁ1
15H, Ad), 3.12 (s, 12H, NMe4); 13C NMR (DMSO-d6)
54.2, 56.9, 278.5; 77Se NMR (DMSO-d6)
1079.1; UV/vis (THF) lmax
(log ) 561 (1.34), 349 (3.35), 228 (3.61) nm.
;
1H NMR (DMSO-d6)
d
1.56, 1.93, 2.04 (br s,
29.0, 36.6, 44.8,
ꢀ
MIshra, N. C.; Ila, H. Org. Biomol. Chem. 2011, 9, 5793; (f) Ceser, V.; Tourneux, J.-C.;
Vujkovic, N.; Brousses, R.; Lugan, N.; Lavigne, G. Chem. Commun. 2012, 2349; (g)
d
€
Farber, C.; Leibold, M.; Bruhn, C.; Maurer, M.; Siemeling, U. Chem. Commun. 2012,
d
227; (h) Katritzky, A. R.; Jischkariani, D.; Salkuja, R.; Hall, C. D.; Steel, P. J. J. Org.
Chem. 2012, 76, 4082; (i) Blake, G. A.; Moerdyk, J. P.; Bielawski, C. W.
3

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