Ambient Temperature Synthesis of High Enantiopurity N-Protected Peptidyl Ketones by Peptidyl Thiol Ester−Boronic Acid Cross-Coupling

Abstract

α-Amino acid thiol esters derived from N-protected mono-, di-, and tripeptides couple with aryl, π-electron-rich heteroaryl, or alkenyl boronic acids in the presence of stoichiometric Cu(I) thiophene-2-carboxylate and catalytic Pd₂(dba)₃/triethylphosphite to generate the corresponding N-protected peptidyl ketones in good-to-excellent yields and in high enantiopurity. Triethylphosphite plays a key role as a supporting ligand by mitigating an undesired palladium-catalyzed decarbonylation−β-elimination of the α-amino thiol esters. The peptidyl ketone synthesis proceeds at room temperature under nonbasic conditions and demonstrates a high tolerance to functionality.