9,10‐Phenanthrenedione‐Catalyzed, Visible‐Light‐Promoted Radical Intramolecular Cyclization of N‐Biarylglycine Esters: One‐Pot synthesis of Phenanthridine‐6‐Carboxylates

Abstract

A visible‐light photoredox cyclization of a series of N‐biarylglycine esters to phenanthridine‐6‐carboxylates using 9,10‐phenanthrenedione (PQ) as a catalyst, white LEDs (7 W) as irradiation source and oxygen from air as a terminal oxidant is described. Also, for the reaction, a feasible mechanism is proposed. The N‐biarylglycine esters are converted into radical intermediates by the action of an excited‐state catalyst (PQ*), which are subsequently subjected to intramolecular cyclization followed by dehydrogenation reactions in one‐pot to afford desired products in high yield. Use of inexpensive catalyst, short reaction time and in situ generation of N‐biarylglycine esters are some of the important advantages of present methodology while compared to rose bengal‐photocatalysted protocol already reported by us.

Substrate-Controlled Three-Component Synthesis of Diverse Fused Heterocycles

“…. 27 Synthesized from 1-(m-tolyl)ethan-1-one (2.68 g, 20 mmol). Purified by flash chromatography (eluent: ethyl acetate + hexane, gradient: 40−60% of hexane) followed by trituration with pentane.…”

“…1 H NMR (400 MHz, DMSO-d 6 ) δ 7.94−7.84 (m, 4H), 7.50−7.32 (m, 6H), 6.00 (d, J = 9.2 Hz, 2H), 2.32 (s, 6H). 13 27 Synthesized from 1-mesitylethan-1-one (3.24 g, 20 mmol). Purified by flash chromatography (eluent: ethyl acetate + hexane, gradient: 40−60% of hexane) followed by trituration with pentane.…”

“…2-(4-Nitrophenyl)-2-oxoacetaldehyde Hydrate (8j•H 2 O). 26,27 Synthesized from 1-(4-nitrophenyl)ethan-1-one (3.30 g, 20 mmol). Purified by flash chromatography (eluent: ethyl acetate + hexane, gradient: 40−60% of hexane).…”

“…1 H NMR (400 MHz, DMSO-d 6 ) δ 9.47 (s, 0.2H), 8.39 (d, J = 8.9 Hz, 0.4H), 8.35 (d, J = 9.0 Hz, 1.6H), 8.32− 8.25 (m, 2H), 7.03 (d, J = 5.0 Hz, 1.6H), 5.66 (bs, 0.8H). 13 27 Synthesized from 1-(furan-2-yl)ethan-1-one (2.20 g, 20 mmol). Purified by flash chromatography (eluent: ethyl acetate + hexane, gradient: 40− 60% of hexane).…”

“…3-(Imidazolidin-2-ylidene)-4-pivaloyl-4,6,7,8-tetrahydro-2Hchromene-2,5(3H)-dione (27). Purified by flash chromatography (eluent: methanol + diethyl ether, gradient 5−10% of methanol).…”