Sequential Photocatalysis for Homologative Diversification of α-Amino Acids to β-Amino Acids Via Phosphonium Ylide Linchpin Strategy.

β-Amino acids serve as crucial building blocks for a broad range of biologically active molecules and peptides with potential as peptidomimetics. While numerous methods have been developed for the synthesis of β-amino acids, most of them require multistep preparation of specific reagents and substrates, which limits their synthetic practicality. In this regard, a homologative transformation of abundant and readily available α-amino acids would be an attractive approach for β-amino acid synthesis.

Chemoselective Cleavage and Transamidation of Tertiary -Methoxybenzyl Amides under Metal-Free Photoredox Catalysis.

A metal-free and mild cleavage of tertiary -methoxybenzyl amides (PMB -amide) under photoredox conditions is developed using Mes-Acr-PhBF and Selectfluor to activate the electron-rich benzylic C-H bond of the PMB moiety. The resulting acyl fluoride intermediate is versatile and facilitates a one-pot transamidation of the PMB -amide. The value of this protocol is highlighted by performing the chemoselective activation of the PMB -amide in bifunctional molecules containing more reactive functionalities than the amide.

Asymmetric phase-transfer catalysis.

Over the past three decades, chiral phase-transfer catalysts (PTCs) have emerged as highly successful organocatalysts in a diverse range of asymmetric reactions. A substantial number of chiral PTCs have now already been discovered and utilized in dependable routes to enantioenriched products. These extend beyond the classical cationic PTCs with the emergence of anionic phase-transfer catalysis and hydrogen-bonding phase-transfer catalysis providing new asymmetric synthetic approaches.

Chemoselective Approach to Versatile Acyl Fluorides by Photoinduced Activation of -Methoxybenzyl Esters.

A new strategy for the metal-free photoinduced activation of -methoxybenzyl esters is developed using Selectfluor and benzil for the generation of acyl fluoride intermediates that enable various transformations. The highlight of this activation method is its high chemoselectivity in the presence of other functionalities, such as esters, amides, and ketones. A synthetic application for the preparation of peptide mimetics that possess two different amide units is also described.

Development of Axially Chiral Pyridylidene Amine Ligands and their Application in Pd-Catalyzed Enantioselective Allylic Substitution.

A series of novel axially chiral pyridylidene amine (PYE) ligands has been developed, and their catalytic capability has been demonstrated in various highly efficient and enantioselective Pd-catalyzed asymmetric allylic substitutions. A density-functional theory (DFT) study explains the preferential enantiocontrol in the key transition states of the axially chiral PYE ligand-promoted Pd-catalyzed allylic alkylation.