Synthesis of the Isodityrosine Moiety of Seongsanamide A-D and Its Derivatives.

The concise and highly convergent synthesis of the isodityrosine unit of seongsanamide A-D and its derivatives bearing a diaryl ether moiety is described. In this work, the synthetic strategy features palladium-catalyzed C(sp)-H functionalization and a Cu/ligand-catalyzed coupling reaction. We report a practical protocol for the palladium-catalyzed mono-arylation of β-methyl C(sp)-H of an alanine derivative bearing a 2-thiomethylaniline auxiliary. The reaction is compatible with a variety of functional groups, providing practical access to numerous β-aryl-α-amino acids; these acids can be converted into various tyrosine and dihydroxyphenylalanine (DOPA) derivatives. Then, a CuI/-dimethylglycine-catalyzed arylation of the already synthesized DOPA derivatives with aryl iodides is described for the synthesis of isodityrosine derivatives.