Indenoindenes, Indenoindoles, and Indenobenzofurans via the Interrupted iso-Nazarov Reaction

Abstract

The cascade carbocation cyclization (CCC) of the secondary benzylic, or the benzhydryl, carbocation by the 2-indene, 2/3-indole, or 2/3-benzofuran followed by the intermolecular nucleophilic addition by H-/allyl-silane or electron-rich arenes, also classifiable as the interrupted iso-Nazarov reaction, provided the corresponding indane-fused indane/indole/benzofuran scaffolds. The initial CCC forged the trans relationship at the two newly formed adjacent stereogenic centers while the latter provided the selective cis stereocontrol at the new ring junction. Starting from achiral alcohols, the reaction sequence furnished the oxygen/nitrogen-containing indane fused-ring tetracyclic systems in moderate to good yields with excellent stereoselectivity on all three contiguous chiral centers.