Application of the peptide claisen rearrangement toward the synthesis of cyclic peptides

[GRAPHICS] Allylic esters of peptides undergo Claisen rearrangement after deprotonation in the presence of tin chloride, giving rise to allylated peptides. Subsequent N-allylation and ring-closing metathesis provides the corresponding cyclic peptides. The yields in the last step strongly depend on the ring size formed.