A rhodium-catalyzed C-H activation/cyclization approach toward the total syntheses of cassiarin C and 8- O -methylcassiarin A from a common intermediate.

Three short and efficient total syntheses of cassiarin C are reported, from a chromanone common key intermediate. A C-H activation strategy, under rhodium catalysis on its pivaloyl oxime, enabled the installation of the pyridine ring. Dehydrogenation of 8- O -methylcassiarin C afforded 8- O -methylcassiarin A. A kinetic experiment and DFT calculations of the intermediates helped to gain insight into the unusual site- and stereo-specific H/D exchange of cassiarin C in CD 3 OD.