Ca(II)-Catalyzed Cascade Reaction of Tryptamines with
Propargylic Alcohols: Temperature-Driven Ring Opening and Closing
via the Allene Migration Pathway for the Synthesis of Pyrrolo[1,2‑a]indoles
posted on 2024-02-02, 14:33authored byAshok Kale, Su Jeong Kwon, Joohan Lee, Jae Kyun Lee, Kyeong Lee
A temperature-dependent
cascade of reactions between tryptamines
and propargylic alcohols was developed to achieve selective formation
of pyrroloindoline and pyrrolo[1,2-a]indole heterocycles
by Ca(II) catalysis. The cascade consists of electrophilic addition
of allene at the C3 carbon of indole followed by intramolecular cyclization
at 60 °C to yield pyrroloindolines. Furthermore, simultaneous
1,2-allene migration and pyrrolidine ring opening were followed by
intramolecular cyclization via C–N bond formation at reflux
temperature to obtain pyrrolo[1,2-a]indole scaffolds.
A wide range of substrates, a clean reaction profile, scalability,
and good to excellent yields are the advantages of this protocol.