Synthesis of phenanthridines via a novel photochemically-mediated cyclization and application to the synthesis of triphaeridine

Songeziwe Ntsimango; Kennedy J Ngwira; Moira L Bode; Charles B de Koning

doi:10.3762/bjoc.17.152

Synthesis of phenanthridines via a novel photochemically-mediated cyclization and application to the synthesis of triphaeridine

Beilstein J Org Chem. 2021 Sep 8:17:2340-2347. doi: 10.3762/bjoc.17.152. eCollection 2021.

Authors

Songeziwe Ntsimango¹, Kennedy J Ngwira¹, Moira L Bode¹, Charles B de Koning¹

Affiliation

¹ Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, PO Wits 2050, Johannesburg, South Africa.

Abstract

Readily synthesized biphenyl-2-carbaldehyde O-acetyl oximes were exposed to UV radiation affording phenanthridines. The scope and limitations of this novel reaction were explored. For example, exposure of 2',3'-dimethoxy-[1,1'-biphenyl]-2-carbaldehyde O-acetyl oxime to UV radiation afforded 4-methoxyphenanthridine in 54% yield. This methodology was applied to the synthesis of trisphaeridine to afford the product in four linear steps in an overall yield of 6.5% from 1-bromo-2,4,5-trimethoxybenzene.

Keywords: UV irradiation; aromatic compounds; cyclization; iminyl radical; phenanthridines; radical cation; synthesis.

Grants and funding

This research was supported by the National Research Foundation (NRF grant number 105839; NRF Thuthuka, grant number TTK200304507920) Pretoria, South Africa, and the University of the Witwatersrand (Science Faculty Research Council).