Lewis-Acid-Catalyzed Decarboxylative Annulation of 2‑Aminoindole-3-Carboxylate with Ynals Involving [3 + 2] Spirocycloaddition and 2,3-Aza Migration
journal contributionposted on 24.01.2020 by Manda Rajesh, Ravi Kumar, Surendra Puri, Jagadeesh Babu Nanubolu, Maddi Sridhar Reddy
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2-Aminoindole-3-carboxylates undergo a Lewis-acid-catalyzed decarboxylative annulation with ynals to afford dihydrochromeno-fused δ-carbolines through a 2,3-aza migration, via a spirocyclic intermediate generated from an initial [3 + 2] spirocycloaddition. Brønsted acid interference changes the path from a [3 + 2] to a [4 + 2] addition. 2-Aminoindoles without an ester functional group at C3 underwent a different condensation, followed by hetero-Diels–Alder reaction to generate chromeno-fused α-carbolines.