Direct C4-Acetoxylation of Tryptophan and Tryptophan-Containing Peptides via Palladium(II)-Catalyzed C-H Activation.

An efficient regioselective palladium(II)-catalyzed C(sp2)-H 4-acetoxylation of tryptophan and tryptophan-containing peptides is described. This transformation achieves the direct construction of C-O bonds at the tryptophan C4-position and features good functional group tolerance. The 4-hydroxyl compound was obtained by removing acetyl after C4-acetoxylation of tryptophan derivatives and tryptophan-containing dipeptides. This method provides a novel strategy for the synthesis of 4-substituted tryptophan derivatives and modification of tryptophan-containing peptides.