Indium-catalyzed direct preparation of dibenzyl sulfides from benzyl alcohols and elemental sulfur with a hydrosilane and its application to the preparation of dibenzyl selenide

Article abstract of DOI:10.1016/j.tetlet.2015.12.109

We describe how a reducing system composed of InI₃ and a hydrosilane efficiently and directly introduce elemental sulfur into the structure of dibenzyl sulfides via a nucleophilic substitution of benzyl alcohols. Also, we describe the application of this reducing system in the direct preparation of a dibenzyl selenide derivative with selenium.

Full text of DOI:10.1016/j.tetlet.2015.12.109

Accepted Manuscript
Indium-Catalyzed Direct Preparation of Dibenzyl Sulfides from Benzyl Alco-
hols and Elemental Sulfur with a Hydrosilane and Its Application to the
Preparation of Dibenzyl Selenide
Takahiro Miyazaki, Masahiro Katayama, Shunsuke Yoshimoto, Yohei
Ogiwara, Norio Sakai
PII:
S0040-4039(15)30528-1
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.12.109
TETL 47156
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
19 November 2015
23 December 2015
28 December 2015
Please cite this article as: Miyazaki, T., Katayama, M., Yoshimoto, S., Ogiwara, Y., Sakai, N., Indium-Catalyzed
Direct Preparation of Dibenzyl Sulfides from Benzyl Alcohols and Elemental Sulfur with a Hydrosilane and Its
Application to the Preparation of Dibenzyl Selenide, Tetrahedron Letters (2015), doi: http://dx.doi.org/10.1016/
j.tetlet.2015.12.109
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Indium-Catalyzed Direct Preparation of
Dibenzyl Sulfides from Benzyl Alcohols and
Elemental Sulfur with a Hydrosilane and Its
Application to the Preparation of Dibenzyl
Selenide
Takahiro Miyazaki, Masahiro Katayama, Shunsuke Yoshimoto, Yohei Ogiwara, and Norio Sakai*

1
Tetrahedron Letters
journal homepage: www.els evier.com
Indium-Catalyzed Direct Preparation of Dibenzyl Sulfides from Benzyl Alcohols
and Elemental Sulfur with a Hydrosilane and Its Application to the Preparation
of Dibenzyl Selenide
Takahiro Miyazaki, Masahiro Katayama, Shunsuke Yoshimoto, Yohei Ogiwara, and Norio Sakai*
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science (RIKADAI), Noda, Chiba 278-8510, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
We describe how a reducing system composed of InI3 and a hydrosilane efficiently and directly
introduces elemental sulfur into the structure of dibenzyl sulfides via a nucleophilic substitution
of benzyl alcohols. Also, we describe the application of this reducing system in the direct
preparation of a dibenzyl selenide derivative with selenium.
Received in revised form
Accepted
Available online
2009 Elsevier Ltd. All rights reserved
.
Keywords:
Reductive sulfidation
Indium
Elemental sulfur
Dibenzyl sulfide
Dibenzyl selenide
Introduction
Thus, to avoid the troublesome handling of these thiols on a
laboratory scale, we have focused on the development of efficient
sulfidation using an economical and odorless form of elemental
sulfur (sulfur powder). For example, the coupling of S(SmI2)2,
which was derived from sulfur powder and SmI2, with alkyl
halides produces symmetrical alkyl sulfides.7 Also, the coupling
of benzyl chloride with either Na2S8 or Li2S9 produced benzyl
sulfide. On the other hand, there has been several reports
involving a copper(I)-catalyzed coupling of aryl halides with
sulfur powder,10 a rhodium(I)-catalyzed coupling of aryl fluorides
with elemental sulfur,11 a copper(I)-catalyzed coupling of a
mixture of aryl boronic acids and aryl counter parts with
Alkyl thioethers (alkyl sulfides) have been used to construct a
main skeleton for natural products, biologically active
substances, and highly valuable materials, such as polymers for
electronic materials and perfumes.1 Hence, the development of an
efficient procedure for the facile preparation of these thioether
derivatives has attracted the interest of a number of organic,
pharmaceutical and material chemists. Thus far, the Williamson-
type synthesis, the coupling of alkyl halides with alkyl thiols
under the strong basic conditions, has been occupied as a typical
approach to the synthesis of the thioethers.2 Also, reductive
couplings of carbonyl compounds, such as aldehydes or ketones,
with thiols in the presence of an appropriate reducing agent have
recently been developed. For example, the pyridine-borane
complex in CF3CO2H functioned as an effective reducing reagent
in the sulfidation of aldehydes and ketones with thiols.3a Also, the
combination of a Lewis acid, BF3, with Et3SiH effectively
promoted the one-pot sulfidation of carbonyl compounds with
thiols.3b A similar sulfidation was catalyzed by the combination
of a Brønsted acid, TfOH, with Et3SiH.3c Also, we conducted the
reductive preparation of alkyl sulfides via an indium-catalyzed
sulfidation from carboxylic acids and thiols in the presence of
elemental sulfur,12 and
a copper(I)-catalyzed coupling of
aromatic compounds with sulfur powder,13 which led to produce
the corresponding diaryl sulfides and aryl alkyl sulfides.
However, these sulfidations generally require several
complicated experimental steps, and most of them are limited to
the preparation of aryl thioethers. Also, in previous research, the
preparation of sulfides through a combination of alcohols with
elemental sulfur has been insufficient. Therefore, the
development of a facile and straightforward preparation for alkyl
sulfides using elemental sulfur is of interest.
1,1,3,3-tetramethyldisiloxane
conversions described above generally required alkyl thiols,
which have an unpleasant odor.
(TMDS).4,5,6
However,
all
In this context, we reported an indium-catalyzed reductive
coupling of either carboxylic acids or aldehydes with elemental
sulfur leading to the preparation of symmetrical benzyl sulfides.14
Thus, after several examinations, we found as a more convenient
approach to alkyl sulfides, a one-pot preparation of dibenzyl
sulfides from benzyl alcohols and elemental sulfur using a
reducing system composed of an indium(III) compound and a
hydrosilane. In this paper, we report the preliminary results.
∗ Corresponding author. Tel.: +81-4-7122-1092; fax: +81-4-
7123-9890; e-mail: sakachem@rs.noda.tus.ac.jp (N. Sakai).

2
Tetrahedron Letters
Also, we disclose that this procedure could be applied to the
direct preparation of dibenzyl selenide derivative.15
unsubstituted benzyl alcohol was treated with TMDS, benzyl
sulfide (2g) was obtained in a good yield. In contrast, the
sulfidation of electron-rich benzyl alcohol derivatives, such as a
o-methyl or a p-methyl group, with elemental sulfur gave the
corresponding sulfides 2h and 2i in relatively low yields (<
50%). However, the substrate with a tert-butyl group produced
symmetrical sulfide 2j in a practical yield. On the basis of our
previous results, wherein an InBr3-Et3SiH reducing system did
not reduce the ester moiety derived from benzoic acid,17 when the
sulfidation was carried out using the benzyl alcohol with an ester
moiety, contrary to our expectations, a complicated mixture was
formed rather than the corresponding sulfide 2k. On the other
hand, the benzyl alcohol with a thioether moiety under the
optimal conditions produced the desired benzyl sulfides 2l in a
55% yield. Thus far, although direct conversion from a benzyl
alcohol and an appropriate sulfur source to a symmetrical
dibenzyl sulfide skeleton was limited to several methods
involving Na2S/palladium nitrate,18 and CO/H2S/Co3(CO)8,19 our
procedure using an benzyl alcohol and elemental sulfur provided
an alternative approach. Unfortunately, when the reaction was
conducted with a benzyl alcohol derivative that has a branched
carbon at the benzyl position and several alkyl alcohols, the
corresponding benzyl sulfide derivatives were not obtained at all.
Results and discussion
Initially, p-chlorobenzyl alcohol (1a: 0.6 mmol) and elemental
sulfur (0.3 mmol) was chosen as an initial model (Table 1).16 On
the basis of our previous work, when the mixture was treated
with 10 mol % of InCl3 and triethylsilane (Et3SiH) in 1,2-
dicholorethene (0.6 mL) at 80 ˚C for 20 h, the desired
symmetrical sulfide 2a was obtained in a 26% yield (entry 1).
Using a stronger Lewis acid, InBr3 (5 mol %), the corresponding
yield was improved to 59% (entry 2). Furthermore, the use of InI3
produced sulfide 2a in an 80% isolated yield after the common
chromatography (entry 3). By contrast, a strong Lewis acid,
In(OTf)3, and a relatively weak Lewis acid, In(OAc)3, both
formed a complicated mixture, though the starting benzyl alcohol
1a was quickly consumed in both cases (entries 4 and 5). The use
of 1,1,3,3-tetramethyldisiloxane (TMDS) and PhSiH3, instead of
Et3SiH, led to a slight decrease in the yield of the expected
sulfide 2a (entries 6 and 7). Unfortunately, running the
sulfidation with PhMe2SiH produced a lower yield (entry 8).
Also, decreasing of the equivalent of Et3SiH to 2 equiv resulted
in the product yield of 60% (entry 9). Moreover, 1 equiv of
Et3SiH could not sufficiently activate S8 to generate a subsequent
nucleophilic sulfur species (entry 10).
Table 2. Preparation of various dibenzyl sulfidesa
Table 1. Optimization of the reaction conditions
entry
InX3
hydrosilane
(Si-H: equiv)
Et3SiH (3)
Et3SiH (3)
Et3SiH (3)
Et3SiH (3)
Et3SiH (3)
TMDS (3)
PhSiH3 (3)
PhMe2SiH (3)
Et3SiH(2)
Et3SiH(1)
GC yield
(%)
26
59
80b
0
a
1
2
InCl3
InBr3
InI3
3
4
In(OTf)3
In(OAc)3
InI3
5
0
6
60
60
45
60
0
7
InI3
8
InI3
9
InI3
10
InI3
a InCl3 (10 mol %). b Isolated yield.
The scope and limitations for the sulfidation of benzyl
alcohols under the optimal conditions was next investigated, and
the results are listed in Table 2. For substrates with an electron-
withdrawing group, such as a fluoro, a bromo and a chloro atom,
with no relation to the location of the substituent on the benzene
ring, benzyl alcohols were cleanly converted to the symmetrical
sulfides 2b-2e in relatively good yields. When the sulfidation of
m-chloro- or o-chloro-substituted benzyl alcohols was conducted
with TMDS (Si-H: 3 equiv), instead of Et3SiH, the corresponding
symmetrical sulfides 2d and 2e were obtained in good yields. On
the other hand, the use of 4-biphenyl methanol did not produce
the expected sulfide 2f at all with a complicating mixture
including 4-methylbiphenyl. When the sulfidation with an
a Isolated yield. b TMDS (3 equiv). c A complicating mixture.
Since there are several chemical resemblances between
elemental sulfur and the same group 16 elements, we used
selenium in an attempt to apply the present method to prepare
dibenzyl selenide (Scheme 1).5c,11b,13,20 Multi-stepwise reactions
have been studied extensively wherein selenium was initially
activated by an alkyl lithium, a Grignard reagent and LiAlH4 to

3
generate a selenolate anion followed by a subsequent SN2
reaction with alkyl halides to produce the corresponding
selenides.21 However, the direct preparation of selenides using
electrophilic substrates, such as an alcohol, selenium and a
hydrosilane has not been investigated widely.22,23 Hence, when
the mixture of benzyl alcohol 1a and elemental selenium was
treated with our reducing system, the desired bis(p-chlorobenzyl)
selenide (3a) was successively isolated in a 45% isolated yield.
The InI3-Et3SiH reducing systems could activate selenium.
Initially, the silylation of a benzyl alcohol with triethylsilane
occurred to produce the correspoding benzyl silyl ether. Then, the
silyl ether was nucleophilically substituted by the disilathiane,
which was derived from the hydrosilane and elemental sulfur,
giving the corresponding benzyl silyl sulfide intermediate.25 In
the first route, a self-condensation between two benzyl silyl
sulfides proceeds, finally producing the symmetrical sulfide. In
the second route, a crossed-condensation of the benzyl silyl
sulfide with the benzyl silyl ether occurred, leading to the
production of a similar final sulfide.26
Scheme 1. Applying to the direct preparation of a dibenzyl
selenide
Conclusions
We demonstrated a facile and straightforward preparation for
symmetrical benzyl sulfides from a variety of benzyl alcohols
and elemental sulfur using an InBr3-Et3SiH reducing system.
Also, odorless and economical elemental sulfur was utilized as a
useful sulfur source of a symmetrical dibenzyl sulfide. Also, this
reducing system with a hydrosilane could be applied to the
activation of selenium, which led to succeed in the direct
preparation of a dibenzyl selenide derivative involving a C-Se
bond formation. Further investigation into the substrate scope
other than benzyl alcohols in this reaction is now in progress.
To further understand the reaction path of the sulfidation,
several control experiments were performed (Scheme 2). When
the mixture of benzyl alcohol (1g) and Et3SiH was treated with 5
mol % of InI3, the corresponding silyl ether was cleanly produced
in a 42% GC yield. This result implied that the indium catalyst
effectively activated a benzyl alcohol, which led to facilitate the
subsequent silylation. Practically, when the similar silylation was
performed without InI3, the expected silylation did not occur.
Also, when the reaction of benzyl trimethylsilyl ether with
bis(trimethylsilyl)sulfide was conducted in the presence of 5 mol
% of InI3, the expected symmetrical sulfide 2g was obtained in a
77% GC yield. Both results showed that the sulfidation series
goes through the benzyl silyl ether intermediate, and that a
disilathiane behaves as one of the intermediates in the sulfidation
series. Moreover, we already confirmed that the disilathiane
intermediate was formed from the corresponding hydrosilane and
S8 (0.5 equiv to the hydrosilane) in the presence of 5 mol % of
InI3.14,24
Acknowledgments
This work was partially supported by a Grant-in-Aid for
Scientific Research (C) (No. 25410120) from the Ministry of
Education, Culture, Sports, Science and Technology (MEXT).
We deeply thank Shin-Etsu Chemical Co., Ltd., for the gift of
hydrosilanes.
References and notes
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Scheme 2. Control experiments
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Scheme 3. Plausible reaction mechanism for the sulfidation
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4
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24. When the reaction of Me2PhSiH with elemental sulfur was carried
out in the absence of InI3, the formation of the corresponding
disilathiane was not observed.
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16. General procedure for the indium-catalyzed reductive preparation
of dibenzyl sulfides (or selenides): To a 5 mL screw-capped vial
containing a freshly distilled 1,2-dichloroethane (0.6 mL) were
successively added under N2 atmosphere, a benzyl alcohol (0.6
mmol), elemental sulfur (or selenium) [0.30 mmol of S atoms, 9.6
mg (or 0.60 mmol of Se atoms, 48 mg)], InI3 (0.030 mmol, 15 mg)
and Et3SiH (or TMDS) (1.8 mmol). The vial was then sealed with
a cap that contained a PTFE septum, the mixture was stirred at 80
˚C (bath temperature), and monitored by GC or TLC analysis for
20 h. After the reaction, the resulting mixture was filtered by a
Celite pad, and was then evaporated under reduced pressure. The
25. For the paper of the substitution of alkyl acetates with a thiosilane,
see: Nishimoto, Y.; Okita, A.; Yasuda, M.; Baba, A. Org. Lett.
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crude product was purified by
a
preparative thin-layer
chromatography (SiO2: 99 / 1 = hexane / EtOAc) to give the
corresponding dibenzyl sulfide (or selenide).
26. We already reported that the cross-over reaction of a benzyl silyl
ether with a benzyl silyl thioether was examined, see also ref. 14.
17. a) Sakai, N.; Moriya, T.; Fujii, K.; Konakahara, T. Synthesis 2008,
3533-3536. (b) Sakai, N.; Moriya, T.; Konakahara, T. J. Org.
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Supplementary Material
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1
Copies of the H and 13C NMR spectra of dibenzyl sulfides
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Chem. Soc., Perkin Trans. 1 1998, 1973-2004.
and bis(4-chlorophenyl) selenide that were produced by this
procedure were supplied.