Palladium/Unichiral Ligand‐Catalyzed Decarboxylative Asymmetric Protonation of Racemic β‐Oxoallyl Esters

Abstract

Scheme 9. DAPs leading to a-arylisoflavanones (R 1 ,R 2 ,R 3 ,R 4 = H, Me,OMe;R 2 -R 3 = CH 2 OCH 2 ).Scheme 10. DAPs leading to 7-(naphthalen-2-ylmethoxy)isoflavanones (R 1 ,R 2 ,R 3 ,R 4 = H, OMe,R 1 -R 2 = CHCH=CHCH). Scheme11. DAPs leading to a-aryloxindoles (R 1 ,R 2 ,R 3 , R 4 = H, Me,OMe;R 2 -R 3 = CH 2 OCH 2 ). Scheme 21. Guirysmechanistic proposal for the palladium-catalyzed DPAofa llyl b-keto esters with formic acid. Scheme 22. Plausible enantiodetermining transition state for the Meldrumsa cid-mediated DAPof( AE)-18a. Scheme 23. Alternative plausible enantiodetermining transition state for the Meldrumsacid-mediated DAPof( AE)-18a. Scheme 24. Plausible enantiodetermining transition state for the Meldrumsa cid-mediated DAPof( AE)-2a. Scheme 25. Plausible enantiodetermining transition state for the Meldrumsa cid-mediated DAPof( AE)-7a. Scheme 26. Plausible enantiodetermining transition states for the formic acid-mediated DAPof(AE)-7a. Scheme 27. Plausible enantiodetermining transition states for the formic acid-mediated DAPs of (AE)-2a and (AE)-7a.

Enantioselective Protonation of Cyclic Carbonyl Ylides by Chiral Lewis Acid Assisted Alcohols

“…To date, several strategies have been employed for enantioselective protonation, including (a) protonation of enol ethers and enol esters by chiral proton donors, (b) protonation of enolates generated by chiral Brønsted base catalysts, and (c) protonation of Pd enolates by achiral Brønsted acids (Scheme 1). [1g,k,l] In the cases involving chiral proton catalysis, pre‐preparation of the enolate equivalents is typically required for activation of the carbonyl compounds. In contrast to these strategies, we envisioned a novel enantioselective protonation of in situ‐generated transient enolate equivalents.…”

Metal‐Ion/Metal Nanoparticle‐Anchored Porous Organic Polymers as Efficient Catalysts for Organic Transformations – A Recent Overview

“…[49] To overcome these problems, transition-metal catalysts were employed in combination with mild oxidants. [50] In this context, Song et al reported the use of Pd/Cu-loaded POP for the heterogeneous oxidation of alkynes to 1,2-diketones using O 2 as the oxidant (Scheme 10). [51] A wide range of substituted alkynes with various functional groups were oxidized to their corresponding 1,2-diketones in high to excellent yields (76-99%).…”

“…Typically 1,2‐diketones are prepared by the oxidation of 1,2‐diaryl/alkyl‐alkynes using strong oxidants such as KMnO 4 , and organic peroxides, and these oxidants suffer from issues such as functional group tolerance, and waste disposal problems [49] . To overcome these problems, transition‐metal catalysts were employed in combination with mild oxidants [50] . In this context, Song et al .…”

Origin of Protonation Side Products in Pd-Catalyzed Decarboxylative Allylation Reactions: Evidence for In Situ Modification of Triphenylphosphine Ligand

“…22 Further work to expand the types of substrates for decarboxylative protonation has been since carried out and this has been reviewed extensively recently by Guiry 23 and Muzart. 24 Notably, independent mechanistic experiments have demonstrated that formic acid is not the sole proton source (Figure 2d). 22,25 Troubled by the lack of mechanistic understanding of the origin of the proton, as well as believing that there may be wider implications for the DcA field, we undertook a mechanistic study to attempt to determine the source of this atom.…”