Synthesis of highly substituted cryptophane derivatives

We report the synthesis of new cryptophane derivatives 1-4 bearing nine (1, 2) and twelve (3, 4) methoxy substituents. These compounds represent the first examples of cryptophane derivatives bearing more than six substituents attached on the benzene rings. The preparation of these highly substituted cryptophanes was achieved due to the synthesis of a new cyclotrisyringyl derivative obtained from the reaction of a protected syringyl alcohol in the presence of a catalytic amount of scandium triflate Sc(OTf)3. This reaction also provides the protected cyclotetrasyringyl derivative in low yield (7%), which was fully characterized by (1)H NMR, IR, and X-ray crystallography. In contrast to what is observed for the cryptophane-A congener, the synthesis of these highly substituted cryptophanes gives rise to the two anti- and syn-diastereomers. These compounds have been fully characterized, and their X-ray structures have been obtained to ascertain the stereochemistry of these new cryptophane derivatives.