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severe disadvantages such as harsh conditions, the necessity for several steps, elaborated
precursors, and stoichiometric chemical oxidant. Furthermore, larger amounts of
reagent waste, sophisticated synthetic conditions such as inert atmosphere as well as
high-temperature, emerge as unfavorable aspects from the aforementioned approaches.
Therefore, the development of a sustainable, nonhazardous and efficient method for the
synthesis of acetylenic sulfones is consequently an important goal in organic chemistry.
In the past decade, electrochemistry has attracted continuous interest due to its inher-
ently safe nature and access to extraordinary reaction pathways. Electro-organic chemis-
try can be seen as a green alternative to classical organic chemistry owing to the fact
that it reverts solely to the electric current as an inexpensive and sustainable oxidizing
or reducing agent, which minimizes the amount of waste dramatically.[12] Recently, sul-
finates can be readily oxidized into the corresponding sulfonyl radicals and would be
trapped by various electrophilic coupling partners under electrochemical conditions. For
example, Wang and coworkers reported an electrochemical decarboxylative sulfonyla-
tion of cinnamic acids with sodium sulfinates to a,b-unsaturated phenyl sulfones by
employing a constant current setup in undivided cells.[13] Furthermore, halide mediated
oxidations of aryl sulfinates have also been developed in the preparations of oxindole
and indenones.[14] However, the alkynylcarboxylic acid as coupling partner in electro-
organic chemistry is not explored. Herein, we wish to present a novel metal-free and
oxidant-free protocol for electrochemical decarboxylative sulfono functionalization using
the reaction of arylacetylenic acids with sodium sulfinates, to provide a range of arylace-
tylenic sulfones molecules.
Results and discussion
The initial exploration of this reaction was carried out using 3-phenylpropiolic acid (1a)
and sodium benzenesulfinate (2a) as coupling partners to determine the optimal reac-
tion conditions and the results were summarized in Table 1. To our delight, when 3-
phenylpropiolic acid (1a, 0.5 mmol) was treated with sodium benzenesulfinate (2a,
1.0 mmol) in a solution of LiClO4 (1.0 mmol) in a solvent mixture CH3CN/H2O
(7/1 mL), in a undivided cell with graphite rod (/ 6 mm) as an anode, Pt plate
(10 mmꢀ 10 mm) as a cathode under a constant current (20 mA). The corresponding
acetylenic sulfone 3a was obtained in a yield of 32% after the reaction proceeded at
n
room temperature for 2 h (Table 1, entry 1). Other electrolytes, such as Bu4NClO4,
n
n
nBu4NPF6, Et4NPF6, Et4NOTs, Bu4NBF4 and Bu4NBr, were screened (Table 1, entries
n
2–7), and it was found that Bu4NPF6was the most efficient electrolyte for this electro-
chemical reaction (Table 1, entry 3). Subsequently, other various mixture solvents, such
as 1,4-dioxane/H2O, DMF/H2O, iPrOH/H2O, CH3OH/H2O, and THF/H2O, were
screened and found that these types of solvent mixtures were inefficient (Table 1, entries
8–12). Moreover, it was found that only a trace of the desired product 3a was obtained
by replacing the solvent mixture with a single solvent (CH3CN or H2O) (Table 1,
entries 13 and 14). Next, the electrode materials were screened and it was noted that
graphite as the working electrode and Pt plate as the counter electrode is the best. For
example, when graphite or Pt plate was used as the working electrode and the counter
electrode, respectively, only trace amount of 3a was obtained (Table 1, entries 15 and
Zhong, Qihao
