Iron(ii)-catalyzed annulation to construct novel quinone-fused cyclopenta[2,1-b]indoles: a promising type I photosensitizer

Abstract

A series of novel quinone-fused cyclopenta[2,1-b]indoles was designed and conveniently constructed by an iron(II)-catalyzed annulation reaction from indolynaphthoquinones and 1,3-dicarbonyl compounds. This process involved Michael addition/radical cyclization/aromatization that achieved cyclization products with medium-to-excellent yields. These compounds exhibited near-infrared absorption and can produce O₂˙⁻. Electrochemical tests also confirmed the excellent electron-transferring ability of compound 3af, which also demonstrated excellent type I PDT effects in tumor cells.