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 eta(3):eta(1)-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)(PCy(3)). The scission of the nickel-oxygen bond of the allylalkoxy complexes with ZnMe(2) leading to eta(3)-allyl(methyl)nickel was very efficient to suppress the reverse reaction of the oxidative cyclization. The methylated eta(3)-allylnickel compound underwent the reductive elimination. The carbonylative coupling reaction of the eta(3)-allyl(methyl)nickel proceeded as well under a carbon monoxide atmosphere. Similarly, the addition of Me(3)SiCl to eta(3):eta(1)-allylalkoxynickel complexes was also efficient for the inhibition of the reverse reaction. The resulting eta(3)-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 eta(3):eta(1)-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 eta(3):eta(1)-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 eta(3):eta(1)-allylalkoxynickel containing phenylacetoaldehyde, an isomer of styrene oxide.