Metal-Free Dearomatization: Direct Access to Spiroindol(en)ines in Batch and Continuous-Flow

Prabhat Ranjan; Gerardo M Ojeda; Upendra K Sharma; Erik V Van der Eycken

doi:10.1002/chem.201805945

Metal-Free Dearomatization: Direct Access to Spiroindol(en)ines in Batch and Continuous-Flow

Chemistry. 2019 Feb 18;25(10):2442-2446. doi: 10.1002/chem.201805945. Epub 2019 Jan 21.

Authors

Prabhat Ranjan¹, Gerardo M Ojeda^{1

2}, Upendra K Sharma¹, Erik V Van der Eycken^{1

3}

Affiliations

¹ Laboratory for Organic & Microwave-Assisted Chemistry (LOMAC), Department of Chemistry, University of Leuven (KU Leuven), Celestijnenlaan 200F, 3001, Leuven, Belgium.
² Center for Natural Products Research, Faculty of Chemistry, University of Havana, ZapatayG, 10400, Havana, Cuba.
³ People's Friendship University of Russia, RUDN University), Miklukho -Maklaya street 6, 117198, Moscow, Russia.

PMID: 30507048
DOI: 10.1002/chem.201805945

Abstract

A metal-free, phosphine-catalyzed intramolecular "umpolung Michael addition" on alkynes to form spiroindol(en)ines is reported. This nucleophilic catalysis enables the formation of a wide scope of five- and six-membered spiroindol(en)ines in moderate to excellent yields in batch as well as under continuous-flow conditions. Triphenylphosphine-catalyzed nucleophilic activation of alkynes allows the exclusive formation of exo-product under mild reaction conditions.

Keywords: dearomatization; flow chemistry; indoles; organocatalysis; spiroindolenine.

Grants and funding

721290/Horizon 2020-Research and Innovation Framework Programme