We report a scandium-catalyzed [3+2] annulation of alkylideneoxindoles with allenylsilanes for the enantioselective formation of spirooxindoles in high yield and stereospecificity. The spirooxindole scaffold has gained significant attention in medicinal chemistry and drug discovery with representation in natural alkaloids and pharmaceutical lead compounds. In addition to challenges for enantioselective construction of the spirocenter, there are also challenges incorporating functional handles into the newly formed ring system for further synthetic manipulation. Using a Sc(OTf)<sub>3</sub>/pybox/BArF complex, we have demonstrated that the spiroannulation of allenylsilanes affords products with &gt;94:6 diasteromeric ratio and &gt;90:10 enantiomeric ratio. The annulation products possess a cyclopentene vinylsilane that can be transformed to yield vinylic bromides for organometallic cross-coupling reactions. The oxidation of the Si-C bond under Tamao-Fleming conditions provides access to cyclopentanone spirooxindoles. The role of the counterion, ligand, and scope of allenylsilanes to control selectivity will be discussed. A competition experiment for the first direct comparison of nucleophilicity between allyl- and allenylsilanes will be presented.

Catalytic asymmetric [3+2] annulation with allenylsilanes for the synthesis of spirocyclopentene oxindoles with vinylsilane functionality

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.