Synthesis of peptide alkaloids-III. Amino acids and peptides-XXXII. Synthesis of dihydro-zizyphine A and B

Recently we described² a new cyclisation method for the synthesis of ansa peptides by hydrogenolysis of Z-pentafluorophenyl ester and ring closure on the surface of the palladium catalyst. We applied this reaction to the synthesis of the 14-membered ansa peptide dihydro-zizyphine G¹. Here we wish to report the synthesis of the 13-membered ansa peptides dihydro-zizyphine A ($\text{8a}$) and B ($\text{9a}$)³.