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

Abstract

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.

α‐Olefins as Alkenylmetal Equivalents in Catalytic Conjugate Addition Reactions

“…Moreover, the stereoselectivity with respect to formation of the enolsilane is at least 92:8. Unsaturated ketones are also effective electrophiles (entries [5][6][7][8][9][10][11] but proceed with lower selectivity in some cases.…”

“…As demonstrated in entry 9, electron-rich enones are superior electrophiles, and certain heterocycles are also tolerated (entries [10][11]. Despite reduced selectivity, reactions with furan-and thiophene-containing enones proceed in high chemical yield.…”

Asymmetric Boron Conjugate Additions to Enones in Water Catalyzed by Copper(0)

“…If we take the empirical information into consideration, it is likely that the reaction pathway would involve oxidative cyclometalation as a ratedetermining step, in accord with some reported examples (Scheme 3). [29] The subsequent transmetalation with 2 would furnish a boron enolate intermediate. Reductive elimination could then release the 1,4-diborated product.…”

Nickel-catalyzed reactions of enone with ethylene

“…We recently demonstrated the first example of a nickel-catalyzed direct conjugate addition reactions of simple alkenes, such as styrene, to enones, which is a very straightforward process to introduce an alkenyl group to the β-carbon of enones by the addition of a carbon-hydrogen bond (Scheme 3) [10; 11]. In this reaction, oxidative cyclization of alkenes and enones with nickel(0), giving a nickelacycle intermediate [12][13][14][15][16], was proposed as a key reaction step.…”