Cooperativity between the Substrate and Ligand in Palladium-Catalyzed Allylic Alkylation Using 1-Aryl-1-propynes

Area of Science:

• Organic Chemistry
• Catalysis
• Organometallic Chemistry

Background:

• Allylic alkylation is a crucial carbon-carbon bond-forming reaction in organic synthesis.
• Palladium-catalyzed allylic alkylation often requires specific directing groups or pre-activation of substrates.
• Developing efficient and versatile catalytic systems for allylic alkylation remains an active area of research.

Purpose of the Study:

• To investigate the utility of a monoprotected amino acid, Bz-Gly-OH, as an auxiliary in palladium-catalyzed allylic alkylation.
• To elucidate the mechanism by which Bz-Gly-OH facilitates the reaction.
• To explore the potential for asymmetric allylic alkylation using this new catalytic system.

Main Methods:

• Enamine-palladium catalysis involving Bz-Gly-OH with various carbonyl compounds (ketones, β-keto esters, aldehydes).
• Density functional theory (DFT) calculations to model reaction intermediates and transition states.
• Analysis of reaction products to determine efficiency and selectivity.

Main Results:

• Bz-Gly-OH effectively promotes the allylic alkylation of diverse carbonyl compounds.
• DFT calculations indicate that Bz-Gly-OH assists enamine formation and subsequent outer sphere attack on the π-allylpalladium complex.
• Preliminary results suggest the feasibility of asymmetric allylic alkylation, indicating a novel bifunctional catalytic mode.

Conclusions:

• Bz-Gly-OH serves as an effective auxiliary for palladium-catalyzed allylic alkylation.
• The reaction proceeds via an outer sphere mechanism involving Bz-Gly-OH-mediated enamine formation.
• This work introduces a new strategy for asymmetric allylic alkylation, highlighting a novel bifunctional catalysis approach.