Reversible Carbon−Carbon Bond Formation between 1,3-Dienes and Aldehyde or Ketone on Nickel(0)

The reversible oxidative cyclization of dienes and aldehydes with nickel(0) proceeded to give
η3:η1-allylalkoxynickel complexes. The treatment of these complexes with carbon monoxide led to the
formation of the corresponding lactone and/or the regeneration of a butadiene and an aldehyde concomitant
with the formation of Ni(CO)3(PCy3). The scission of the nickel−oxygen bond of the allylalkoxy complexes
with ZnMe2 leading to η3-allyl(methyl)nickel was very efficient to suppress the reverse reaction of the oxidative
cyclization. The methylated η3-allylnickel compound underwent the reductive elimination. The carbonylative
coupling reaction of the η3-allyl(methyl)nickel proceeded as well under a carbon monoxide atmosphere.
Similarly, the addition of Me3SiCl to η3:η1-allylalkoxynickel complexes was also efficient for the inhibition of
the reverse reaction. The resulting η3-1-siloxyethylallylnickel complex was treated with carbon monoxides
followed by the addition of MeOH to give the expected hydroxyester. This method is efficient as well even
for the η3:η1-allyl(alkoxy)nickel complex containing acetone as a component, which was so prone to undergo
the reverse reaction hampering its isolation. The isolation of the η3:η1-allylalkoxynickel complex containing
ketone as a component was made easier by the use of heavier butadiene and ketone, such as 2,3-dibenzyl-1,3-butadiene and benzophenone or by the use of cyclobutanone. The reaction with styrene oxide gave
the η3:η1-allylalkoxynickel containing phenylacetoaldehyde, an isomer of styrene oxide.