A Direct and Efficient Total Synthesis of the Tubulin-Binding Agents Ceratamine A and B; Use of IBX for a Remarkable Heterocycle Dehydrogenation

The total synthesis of the tubulin-binding agents ceratamine A and B is reported, along with des-methyl analogs, via a synthetic route that is high-yielding and operationally efficient. The synthetic route involved a Beckmann rearrangement to form an azepine ring precursor, a Knoevenagel condensation to install the benzylic side chain, and an effective imidazole annulation onto an alpha-aminoketone precursor with a protected S-methylisothiourea. Final dehydrogenation proved remarkably facile using IBX.