Regioselective synthetic approach for key precursors of 6-arylbenzo[c]phenanthridin-10-ol derivatives: a useful compound for selective chromogenic recognition of fluoride

Abstract

A regioselective synthetic strategy for 6-aryl-8,9-dihydrobenzo[c]phenanthridine-10(7H)-ones (4) is accomplished using a one-pot four-component reaction by fine-tuning the reaction temperature. DMSO is excellently used as a reactant-cum-solvent to introduce a carbonyl functionality regioselectively at the C-10 position of the benzophenanthridine backbone, via an MCR, which is unknown yet. The elegant features of this strategy are the formation of two CC, one CN, and one CO bonds in a single step, without using a base and an activator for the oxygenation process. Then, a few compounds (4) are easily aromatised to achieve 6-arylbenzo[c]phenanthridin-10-ol derivatives (7) using I₂/DMSO at 100 °C. Nay, a dangling hydroxyl group in 4s, 4u, 4x, and 4z helped them to be employed as promising ‘naked eye’ colorimetric chemosensors for fluoride with limits of detection of 0.65, 0.60, 0.34, and 2.2 ppm, respectively. Moreover, the reversibility of the chemosensors makes them suitable for combinatorial INHIBIT logic gate formulation. The compounds have also been employed for solid-state F⁻ detection via the spot TLC test.