A novel synthetic route for the total synthesis of (±)-uleine

In this study, a new synthetic route for the total synthesis of (±)-uleine is described. The important step in the synthesis of this alkaloid consists of an intramolecular cyclization of the D ring of the azocino[4,3-b]indole skeleton. Reduction of (N-methyl){3-β-ethyl-4-oxo-2,3,4,9-tetrahydrospiro[1H-carbazole-1,2′(1,3)dithiolane]-2-yl}-2-acetamide with borane yielded the corresponding (N-methyl){3-β-ethyl-4-hydroxy-2,3,4,9-tetrahydrospiro[1H-carbazole-1,2′(1,3)dithiolane]-2-yl}-2-acetamide, which underwent acid-catalyzed ring closure to produce azocino[4,3-b]indole core. Finally, the synthesis of (±)-uleine was completed through several steps from the azocino[4,3-b]indole core.