Tetrahedron Letters
An efficient and straightforward route to terminal vinyl sulfones via
palladium-catalyzed Suzuki reactions of a-bromo ethenylsulfones
b
a
b
c,
b,
a
Yewen Fang a, , Meijuan Yuan , Juncong Zhang , Li Zhang , Xiaoping Jin , Ruifeng Li , Jinjian Li
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a School of Chemical Engineering, Ningbo University of Technology, No. 89 Cuibai Rd, Ningbo 315016, China
b College of Chemistry and Chemical Engineering, Taiyuan University of Technology, No. 79 West Yingze Street, Taiyuan 030024, China
c Department of Biology and Pharmaceutical Sciences, Zhejiang Pharmaceutical College, No. 888 Yinxian Avenue East, Ningbo 315100, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A general and simple protocol for the synthesis of
a
-substituted alkenylsulfones has been developed
Received 7 January 2016
Accepted 16 February 2016
Available online 16 February 2016
firstly via palladium-catalyzed Suzuki reactions between
Using a catalyst composed of Pd(OAc)2 and SPhos, a variety of aryl, heteroaryl, and alkylboron reagents
could efficiently couple with -bromo ethenylsulfones under mild conditions. Moreover, it has been
a-bromo ethenylsulfones and organoborons.
a
demonstrated for the first time that vinyl sulfones underwent smooth reduction by diimide generated
from 2-nitrobenzenesulfonylhydrazide.
Keywords:
a-Substituted ethenylsulfones
Ó 2016 Elsevier Ltd. All rights reserved.
Suzuki reaction
Cross-coupling
Palladium catalysis
Diimide reduction
Vinyl sulfones are an important class of organosulfur com-
pounds and ubiquitous in a variety of biologically active molecules
and pharmaceuticals.1 Moreover, they are valuable synthetic inter-
mediates in organic transformations such as Michael addition,2
desulfonylation,3 and cycloaddition reactions.4 Recently, vinyl sul-
fones have found interesting applications in visible light photore-
dox catalysis.5 Owing to the importance of these scaffolds, a
number of synthetic methods are well elaborated. Conventional
methods5,6 include olefination reactions, addition–elimination
sequential reactions, hydrozirconation of 1-alkynyl sulfones, and
the oxidation of vinyl sulfides. Recently, considerable efforts7 have
been devoted to the development of new methods with sulfonyl
chloride, sulfinic acid, sodium sulfinate, or sulfonyl hydrazide as
the sulfone unit in the presence of transition-metal catalyst or
under metal-free conditions.
catalyst ([BrettPhosAu(TA)]OTf) (TA = 1H-benzotriazole) and addi-
tive [Ga(OTf)3] preclude the procedure for the practical applica-
tions. Considering the importance of the
a-substituted vinyl
sulfones, we had great desire to synthesize this kind of high-value
added molecules based on cross-coupling reactions from easily
prepared or commercially available coupling partners using a sim-
ple catalyst.11 Motivated by our recent Letters on the synthesis of
alkenylphosphonates,12 we envisioned that an alternative pathway
for the synthesis of
oped via Suzuki cross-coupling reactions.13 Hereby, we are disclos-
ing an efficient protocol for the synthesis of -substituted vinyl
sulfones via Suzuki reactions of -bromo alkenylsulfones in the
presence of Pd(OAc)2/SPhos catalyst.
For the purpose of optimization of the experimental conditions,
we chose a model reaction between -bromo ethenylsulfone 1a
a-substituted alkenylsulfones could be devel-
a
a
a
Compared to numerous procedures for the preparations of
and 3,4-dimethoxyphenylboronic acid 2a. A series of ancillary
ligands were then evaluated for their efficacy in this C–C bond cou-
pling reactions. As is apparent from Table 1, no product was
observed in the absence of ligand (entry 1). After some experi-
ments, we found that SPhos (entry 8) turned out to be the best
ligand compared to other monophosphine ligands (PPh3, t-Bu3-
PꢀHBF4, and Cy3PꢀHBF4) (entries 2–4) and Buchwald’s ligands14
(XPhos, BrettPhos, and RuPhos) (entries 5–7). The use of precata-
lyst PdCl2dppf, a common catalyst for Suzuki reactions, afforded
only trace products (entry 9). In the next step of the screening pro-
cedure, different bases were examined for their ability to promote
the cross-coupling of the model substrates. The screened inorganic
b-substituted vinyl sulfones,7,8 protocols for the specific synthesis
of
quently, the synthetic applications of
were less explored. In this regard, Shi and co-workers have devel-
oped a general method for the synthesis of -substituted vinyl
a
-substituted vinyl sulfones have been rarely reported.9 Conse-
a-substituted vinyl sulfones
a
sulfones from terminal alkynes and sulfinic acid in the presence
of gold catalyst (Scheme 1).10 However, the unusual and expensive
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Corresponding authors.
0040-4039/Ó 2016 Elsevier Ltd. All rights reserved.