Chemodivergent Chalcogenation of Aryl Alkynoates or N-Arylpropynamides Using 9-Mesityl-10-Methylacridinium Perchlorate Photocatalyst

Abstract

Herein we report a cascaded chalcogenation of aryl alkynoates or N-arylpropynamides using 9-mesityl-10-methylacridinium perchlorate as a visible light photocatalyst to obtain selectively either 3sulfenylated/selenylated coumarins or spiro [4,5]trienones. In a radical initiated process, the spiro-cyclization reaction was favored due to the presence of a -OMe or -F substituent at the para position of the aryl group, which helped to stabilize the allylic radical intermediate formed during the reaction. Otherwise, 6-endo-trig cyclization led to 3-sulfenylated/selenylated coumarins. Overall, the new C−S/C−Se, C−C, and C�O bonds were formed in a single step. The Stern−Volmer quenching study, EPR experiments, light ON-OFF experiments, radical trapping experiments, etc., helped to understand the radical-based mechanism.

Atom Transfer Radical Addition Reactions of Quinoxalin-2(1H)-ones with CBr4 and Styrenes Using Mes-Acr-MeClO4 Photocatalyst

“…To assess the role of the photocatalyst, we conducted an initial reaction in the presence of light but without the Mes-Acr-Me-ClO 4 photocatalyst. Notably, this control experiment revealed that, in the absence of the photocatalyst, no desired product was observed, leaving only the starting material intact (Figure a) . Furthermore, in the presence of radical inhibitors known to evident the radical process, such as 1,1-diphenylethylene, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and BHT (butylated hydroxytoluene), no desirable product was observed (Figure b).…”

“…Notably, this control experiment revealed that, in the absence of the photocatalyst, no desired product was observed, leaving only the starting material intact (Figure 4a). 37 Furthermore, in the presence of radical inhibitors known to evident the radical process, such as 1,1-diphenylethylene, TEMPO (2,2,6,6tetramethylpiperidine-1-oxyl), and BHT (butylated hydroxytoluene), no desirable product was observed (Figure 4b). Additionally, attempts were made to trap the radical intermediate using radical quenchers, but the results were unsatisfactory.…”

“…This involves activating C–Br bonds in CBr 4 and subsequently conducting a trihaloalkyl-carbofunctionalization of styrenes. We employ the 9-mesityl-10-methylacridinium perchlorate or Mes-Acr-MeClO 4 (Fukuzumi) photocatalyst − in conjunction with 3W blue LED (450–470 nm) irradiation. This three-component radical cascade process demonstrates high efficiency in synthesizing derivatives of 1-methyl-3-(3,3,3-tribromo-1-(4-chlorophenyl)­propyl)­quinoxalin-2­(1 H )-one (Figure b) …”

Synthesis of 1,1-Diarylvinylsulfides via Visible-Light-Promoted Cascade Reaction of Alkynoates with Phenyl Disulfides

“…In light of all of above and our previous works, we herein report a simple yet highly efficient synthetic route for DPVS derivatives through visible-light promoted cascade reaction of alkynoates with phenyl disulfides. In our originally designed synthetic methodology, this visible-light promoted reaction could afford 3-sulfenylated coumarin under mild conditions. , Though the desired product is not observed, DPVS can be obtained in high yield under very mild conditions. The reaction can be carried out without any additives and photocatalysts under room temperature (Scheme .4).…”

“…According to above experimental results and previous reports, ,, a cascade radical process is proposed in Scheme . Initially, the phenyl sulfur radical A is generated via S–S bond homolytic cleavage of 2a upon visible light irradiation .…”