The authors’ preliminary mechanistic studies revealed that the presence of an α-heteroatom such as oxygen in 1-sulfonyl glycal 47 could facilitate the cross-coupling of sulfones [17](Scheme 7-B). This precoordination with the nickel catalyst could explain the high regioselectivity of the oxidative insertion step, where the cleavage of the C–S bond adjacent to the oxygen atom is favored. Moreover, The modified conditions without a boronic acid coupling partner yielded 50a in high yield, indicating that the oxidative insertion of 47b by Ni(0) and the desulfination of the resulting phenyl sulfinate are both efficient and straightforward reactions. Based on the above information, the authors proposed a plausible reaction mechanism, as depicted in Scheme 7-C. The regioselective C–S bond insertion of 1-sulfonyl glycal by Ni(0) initiates the reaction pathway, which is hypothesized to be facilitated by a transient formation of a vinyl nickel species 60 . This vinyl nickel species could potentially undergo two distinct pathways: either a desulfination/reductive elimination sequence resulting in61 or a transmetallation step followed by reductive elimination to produce 63 as the final product. The success of the reaction suggests that. the transmetalation process was favored over the desulfination step.
Scheme 7 Synthetic applications and plausible mechanism