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.