Stereoselective coupling of ketone and carboxylate enolates

Flexible Stereoselective Functionalizations of Ketones through Umpolung with Hypervalent Iodine Reagents

“…The method also allowed carbon–carbon coupling reactions by using an enolate as the nucleophile and as the electrophile in the same reaction, thus providing direct access to highly versatile 1,4‐dicarbonyl derivatives. This process was initially reported in 193519 and since that time also used frequently in stereoselective reactions,20 but almost exclusively involving metal enolates. A major limitation lies with the lack of methods that allow for the selective and controlled coupling of enolates under metal‐free conditions and only a few reactions describe the dimerization of trimethylsilyl enol ethers to form 1,4‐diketones 21–24.…”

Experimental and Computational Evidence of the Biradical Structure and Reactivity of Titanium(IV) Enolates

“…Indeed, the very nature of these electronic configurations is, to a large extent, distinct: one corresponds to a closed shell electronic state, whereas the other has a marked open shell, delocalized biradical, character, which requires an electron transfer from the organic ligand to the titanium metal. Therefore, the closed shell electronic configuration would be responsible for the classical nucleophilic reactivity observed for these titanium(IV) enolates 14 whereas the open shell might be the origin of the aforementioned biradical character and the basis for a Homocoupling of certain enolates derived from phenylacetic derivatives 15, 16 and other occasional pieces of evidence in the literature 17 Furthermore, we also fully reported the aminoxylation reactions of titanium(IV) enolates from several chiral platforms with TEMPO that produce α-oxygenated adducts in a highly stereocontrolled manner compatible with a biradical intermediate (Equation and in Scheme 2). 21 Thus, the valence tautomery in titanium(IV) enolates shown in Schemes 1 and 2 is well established, which is also compatible with the observed nucleophilic-like reactivity.…”

Vanadium(V)‐Induced Oxidative Cross‐Coupling of Various Boron and Silyl Enolates

“…In the present study,w ef ocused on combining ketone, ester,a nd amide enolates. Althoughhomocoupling of enolates derived from carboxylic acid derivativesh as already been reported in 1935, [8] their crosscoupling has not been studied extensively.Sofar,asacombination of ester and ketone, oxidative cross-coupling of lithium enolates using electrodes by Tokuda et al, [9] ,a nd CuCl 2 by Saegusa, Ito et al [10] has been reported;h owever,e xamples are quite limited. We also reported af ew cross-coupling examples of silyl enolates.…”