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