Catalytic Asymmetric Reactions of 4‐Substituted Indoles with Nitroethene: A Direct Entry to Ergot Alkaloid Structures
Year: 2015
Type: article
Abstract: A domino Friedel-Crafts/nitro-Michael reaction between 4-substituted indoles and nitroethene is presented. The reaction is catalyzed by BINOL-derived phosphoric acid catalysts, and delivers the corresponding 3,4-ring-fused indoles with very good results in terms of yields and diastereo- and enantioselectivities. The tricyclic benzo[cd]indole products bear a nitro group at the right position to serve as precursors of ergot alkaloids, as demonstrated by the formal synthesis of 6,7-secoagroclavine from one of the adducts. DFT calculations suggest that the outcome of the reaction stems from the preferential evolution of a key nitronic acid intermediate through a nucleophilic addition pathway, rather than to the expected "quenching" through protonation.
Source: Chemistry - A European Journal
Institutions: University of Bologna, Stockholm University, University of Perugia
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2142284606