Tetrahedron Letters
Visible-light-promoted synthesis of diaryl sulfides under air
Boseok Hong a, Juyoung Lee a, Anna Lee a,b,
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a Department of Chemistry, Myongji University, Yongin 17058, Republic of Korea
b Department of Energy Science and Technology, Myongji University, Yongin 17058, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A convergent, organocatalytic visible-light-mediated process for the synthesis of diaryl sulfides has been
developed. A broad range of aryl thiols reacted with various aryl diazonium salts in the presence of eosin
Y under air atmosphere to afford the desired diaryl sulfides in high yields. This novel and environmentally
friendly method provides an alternative route to established synthetic approaches.
Ó 2017 Elsevier Ltd. All rights reserved.
Received 29 April 2017
Revised 27 May 2017
Accepted 2 June 2017
Available online xxxx
Keywords:
Organo-photocatalysis
Diaryl sulfides
Thiols
Introduction
diazonium salts and thiolates.13 In these studies, the reactions
were performed carefully under nitrogen since the intermediate
Sulfur-containing compounds are found in numerous natural
products and pharmaceuticals.1 In particular, diaryl sulfides and
their derivatives are important structural motifs in natural and
synthetic molecules and have shown interesting biological activi-
ties such as HIV protease inhibition, anti-hepatitis C activity,
anti-depression activity, anti-inflammatory and anti-histamine
properties (Scheme 1).1e,2 Moreover, diaryl sulfides have been
employed as organic materials in the field of materials science.3
Furthermore, they are precursors to other sulfur-containing com-
pounds comprising higher-oxidation state-sulfur, which have sim-
ilar important bioactive properties.2f,4
Given the significance of these compounds as important struc-
tural scaffolds in natural products and drug candidates, it is very
important to develop an efficient process for synthesizing diaryl
sulfides. Previous approaches for the synthesis of diaryl sulfides
utilized various transition metals such as Pd,5 Cu,1d,6 Fe,7 Ni,8
Rh,9 Co10 and In.11 These methods provide powerful tools for the
synthesis of diaryl sulfides. However, metal-catalyzed reactions
have some limitations such as using expensive and/or toxic metal
catalysts and sensitive or harsh reaction conditions. A number of
metal-free processes were also investigated; for example, conden-
sation of arenethiols with aryl halides, and nucleophilic substitu-
tion of activated aryl halides with thiols.12 Early studies for the
synthesis of diaryl sulfides reported by the Petrillo group used
metal-free processes that included the use of various aryl
diazosulfide is a potent explosive.
Recently, metal-free CAH thioarylation of electron rich arenes
and heteroarenes using electrophilic sulfur reagents such as sul-
fonyl chlorides,14 sulfonyl hydrazines,15 N-(thio)succinimides,16
sodium sulfinates,17 thiols,18 disulfides,19 sulfoxides2f and
others20 has been developed. Despite these recent advances, a
direct process for the synthesis of diaryl sulfides via photocatalysis
would offer a complementary strategy to the existing synthesizing
methods.
Recently, visible-light-mediated photoredox catalysis has
emerged as a powerful tool in organic synthesis. Ruthenium and
iridium polypyridyl complexes are widely employed in visible light
photocatalysis with great reported success.21 However, based on
the limitations of utilizing transition metals, the development of
green activation modes in photoredox system is very important.
Organic dyes have been used as an attractive alternative to transi-
tion metal photoredox catalysts;22 especially, eosin Y was widely
employed as an organocatalyst in various photoredox processes.23
Herein, we report a mild convergent approach for the synthesis of
diaryl sulfides in the presence of eosin Y via visible light photo-
catalysis (Scheme 2).
Results and discussion
To develop a metal-free protocol, we designed a reaction model
with thiophenol 1a and 4-methoxybenzenediazonium tetrafluo-
roborate 2a in the presence of organo-photocatalysts at room tem-
perature under air atmosphere (Table 1). Various organic dyes
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Corresponding author at: Department of Chemistry, Department of Energy
Science and Technology, Myongji University, Yongin 17058, Republic of Korea.
0040-4039/Ó 2017 Elsevier Ltd. All rights reserved.