Amine Catalyzed Remote [4+2]‐annulation Of Indole Tethered Enal And Oxindole Olefin To Access Optically Pure Hydrocarbazole Spirooxindole Scaffolds

Abstract

This research showcases a methodology for crafting highly intricate hydrocarbazole spirooxindole frameworks endowed with three consecutive stereocenters. Achieved through a trienamine‐catalyzed remote [4+2]‐annulation reaction, the method's significance is underscored by synthesizing an extensive array of library molecules (up to 27 examples). These compounds mimic natural products and exhibit good yields (up to 85%) and exceptional diastereo‐ and enantiomeric ratios (up to 17:1 dr and 99.9:0.1 er). The practicality of our strategy is further exemplified by successfully synthesizing a hexahydroepoxy‐ethanocarbazole spirooxindole scaffold via a sequential [4+2]‐annulation/‐reduction/epoxidation‐cyclization reaction, achieving a 75% overall yield and maintaining an excellent stereoselectivity (99.5:0.5 er).