Visible-Light Mediated Metal-Free 6π-Photocyclization of N-Acrylamides: Thioxanthone Triplet Energy Transfer Enables the Synthesis of 3,4-Dihydroquinolin-2-ones

Abstract

An efficient thioxanthone-catalyzed triplet energy transfer process for the synthesis of 3,4-dihydroquinolin-2-ones via a 6π-photocyclization is reported. Featuring a rare example of a metal-free formal C­(sp2)–H/C­(sp3)–H arylation mediated by visible-light, this work hopes to inspire further interest in these small molecules as sustainable alternatives to existing transition-metal photocatalysts in related processes.

Photoredox Cyclization of N-Arylacrylamides for Synthesis of Dihydroquinolinones

“…Within our ongoing project on sustainable chemistry, herein we report on the first metal- and additive-free visible-light-induced photoredox-neutral photocyclization of N -arylacrylamides (Figure d). Concurrent with our efforts, a related report has appeared . In our catalytic system, 4CzIPN serves basically as the key photosensitizer and low-toxic acetonitrile as reaction media.…”

Visible light-assisted Ni-/Ir-catalysed atom-economic synthesis of spiro[furan-3,1′-indene] derivatives

“…Surprisingly, deuterated product 3aa′ with over 90% D was isolated and confirmed by HRMS and NMR analysis, indicating nonpolar protonation rather than radical hydrogen atom abstraction. Based on the optimization studies (Table S1, ESI,† entries 20 to 23), 19 a control experiments, 19 f and the literature reports, 21 we proposed a plausible mechanism via an EnT pathway rather than SET (Fig. S7, ESI†) 19 g in Scheme 5.…”

Recent progress in organophotoredox reaction

“…In comparison with other aromatic ketones, thioxanthones (TXs) have high triplet energy and a relatively long triplet lifetime, so they have the ability to participate successfully in photocatalytic reactions as organic photocatalysts. 13 In 2021, Petersen 81 reported an efficient thioxanthone-catalyzed triplet energy transfer process for the synthesis of 3,4-dihydroquinolin-2-ones via a 6π-photo cyclization. The proposed mechanism of the reaction is shown in Scheme 49.…”