Selectivity Rules for the Dearomative (3+2) Annulation Reaction Between Substituted Indoles and Oxyallyl Cations

We report a collection of "selectivity rules" for the dearomative (3+2) annulation reaction between substituted indoles and oxyallyl cations. The application of these rules enables us to synthesize four different regioisomeric permutations of the annulation products in a stereoselective fashion. We demonstrated that these products could be further transformed into hexahydro- and tetrahydrocarbazoles by nucleophile-intercepted Beckmann fragmentation (NuBFr) and Beckmann fragmentation (BFr).