Radicals in organic chemistry Propose a mechanism
Why do you think this is a radical reaction?
I have searched a bit this reaction and found the following mechanism: First the diradical formation occurs. The halide ion then donates its two electrons in the formation of a new Br-C bond and radical electron involved is believed to shuttle over a transient C1-C4 bond forming the anion intermediate B. The anion is a powerful base, stripping protons even from DMSO to final product.
See the original paper link for more details: https://pubs.acs.org/doi/10.1021/ja070023e