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

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, exhibit good yields (up to 85 %), exceptional diastereo-, enantiomeric ratios (up to 17 : 1 dr, 99.9 : 0.1 er). The practicality of our strategy is further exemplified by successfully synthesizing a hexahydroepoxyethanocarbazole spirooxindole scaffold via a sequential [4+2]-annulation/-reduction/epoxidation-cyclization reaction, achieving a 75 % overall yield, maintaining an excellent stereoselectivity (99.5 : 0.5 er). We report the asymmetric synthesis of hydrocarbazole spirooxindoles with three contiguous stereocenters via trienamine-catalyzed remote [4+2]-annulation reaction. image