Electrochemical Synthesis of (Aza)indolines via Dehydrogenative [3+2] Annulation: Application to Total Synthesis of (+/-)-Hinckdentine A

An electrochemical synthesis of functionalized (aza)indolines through dehydrogenative [3+2] annulation of arylamines with tethered alkenes has been developed. Previous reported syntheses through similar inter- and intramolecular annulation reactions required noble-metal catalysts and are mostly limited to terminal alkenes or 1,3-dienes. The electrosynthesis employs the easily available and inexpensive ferrocene as the molecular catalyst and is compatible with di-, tri- and even tetrasubstituted alkenes to construct indolines as well as the more challenging azaindolines. Employing the newly developed electrosynthesis as a key step, the total synthesis of marine alkaloid (+/-)-hinckdentine A has been achieved in 12 steps (longest linear sequence) from commercially available materials.