Tantalum-Catalyzed Amidation of Amino Acid Homologues.

A tantalum-catalyzed solvent-free approach for the construction of amide bonds with 1-(trimethylsilyl)imidazole is developed, and the mild reaction conditions are applicable to a wide variety of electrophilic amino acid homologues. This approach delivers a new class of peptides in high yields without any epimerization.