In addition, transition-metal-catalyzed carboxylation of vinyl derivatives, such as haloalkenes [
27–
33], vinyl boronic acid esters [
34–
38], vinyl sodium sulfinates [
39] and so on [
40–
42], has been developed as a robust method to construct
α,
β-unsaturated carboxylic acids. The original configuration of the parent precursor is usually preserved. Transition-metal-free organic synthesis is environmentally benign and sustainable that gained more and more attention in 21 century [
43]. Nevertheless, stereoselective carboxylation of vinyl derivatives under transition-metal-free and mild conditions to produce
α,
β-unsaturated carboxylic acids is elusive. König and coworkers have reported a photocatalytic C—H carboxylation of styrenes to afford
E-cinnamic acids (
Scheme 1b) [
44]. Additionally, synthetic electrochemistry plays an important role for organic transformations [
45–
50]. An electrochemical reduction of
β-bromostyrenes was reported by Kuang and co-workers (
Scheme 1c) [
51]. Notably, either the
E-bromostyrene or the
Z-bromostyrene affords a mixture of cinnamic acids. This is attributed to the low energy barrier to inversion for
α-hydrogen vinyl radicals (for the ethenyl radical is 3.3 kcal/mol) [
52] that leads to a mixture of
cis- and
trans-products. The authors found that the stereospecific electrochemical carboxylation of
β-bromostyrenes was only achieved when the nickel salt is added as a catalyst. The electrochemical defluorinative carboxylation of
gem-difluoroalkenes under transition metal-free conditions has been developed recently, providing the
α-fluoroacrylic acids with the
Z/
E selectivities from 1/2 to 20/1 (
Scheme 1d) [
53]. Thus, stereoselective electrochemical carboxylation of vinyl derivatives remains challenging under transition-metal-free conditions. Given that the easily available organosulfones are versatile building blocks in organic synthesis, they may also serve as promising reaction partners in reductive functionalization [
54–
58]. Herein, we report the electrochemically stereoselective carboxylation of
α,
β-unsaturated sulfones to afford a series of
α,
β-unsaturated carboxylic acids.