Photocatalytic Synthesis of 3‐Sulfanyl‐ and 1,3‐Bis(sulfanyl)indolizines Mediated by Visible Light

Abstract

A metal-free method for the synthesis of 3-sulfanyl indolizines from thiols and 2-arylindolizines, is reported. The reaction is mediated by eosin Y under blue LED light irradiation [a]

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

“…In 2020, Lenardão, Silviera and co-workers disclosed a photocatalytic method for the C(sp 2 )–H sulfenylation of indolizines ( Scheme 233 ). 624 Using EY as a photocatalyst, blue-light irradiation of DMSO solutions of indolizine and thiol substrates under an air atmosphere, 30 examples of C3-selective C(sp 2 )–H mono-sulfenylation were described with yields of 24–88%. With respect to the thiol component, six thiophenols ( 233.1 , 233.2 ) and one aliphatic thiol were demonstrated to be efficacious reaction partners, with lower yields observed for 2-chlorobenzenethiol and n -propanethiol.…”

UVA Light‐promoted Catalyst‐free Cyclization of Vinyl Selenides: Green and Efficient Synthesis of C3‐Unsubstituted 2‐Selanyl Benzochalcogenophenes

“…The substrate and the solvent were selected based on our previous results using copper-catalysis, [14] while the light wavelengths were chosen after our recent development on visible light-mediated transformations. [15] Under these conditions, however, no cyclization product 2 a was detected after irradiation for 24 h (Table 1, entries 1-2). Then, in an attempt to activate the reaction system, a slightly more energetic light source was used, and the reaction was performed under irradiation with two insect killer UVA lamps (λ ~400-315 nm, peak at 365 nm, 15 W; see Figure S1, in the SI for pictures of the apparatus).…”

“…The optimization study of the light‐promoted reaction was initially conducted using ( E )‐{2‐[2‐bromo‐2‐(phenylselanyl)vinyl]phenyl}propylsulfane 1 a as substrate and MeNO 2 as solvent under irradiation with 50 W blue (λ∼495–450 nm) and white LEDs, aiming to prepare the 2‐selanyl benzothiophene 2 a . The substrate and the solvent were selected based on our previous results using copper‐catalysis, [14] while the light wavelengths were chosen after our recent development on visible light‐mediated transformations [15] . Under these conditions, however, no cyclization product 2 a was detected after irradiation for 24 h (Table 1, entries 1–2).…”

Sonochemistry and Copper Catalysis: An Efficient Duo in the Synthesis of Chalcogenylindolizines

“…For instance, Cao and co‐workers reported in 2018 a peroxide‐mediated synthesis of 3‐sulfanylindolizines under thermal conditions, in which 1,3‐bis(sulfanyl)indolizines could be accessed in the presence of catalytic KI (Scheme , #1). The same classes of compounds were obtained by us through a visible‐light‐promoted sulfanylation of indolizines, after up to 24 h of irradiation with blue LED, using air oxygen as an oxidant . Alternatively, 1,3‐bis(selanyl)indolizines were prepared in poor to excellent yields by the electrochemical diselenylation of indolizines, via a multicomponent process between 2‐picolines, α‐bromoketones and diorganyl diselenides (Scheme , #2) .…”

“…The same classes of compounds were obtained by us through a visible-light-promoted sulfanylation of indolizines, after up to 24 h of irradiation with blue LED, using air oxygen as an oxidant. [12] Alternatively, 1,3-bis(selanyl)indolizines were prepared in poor to excellent yields by the electro-chemical diselenylation of indolizines, via a multicomponent process between 2-picolines, α-bromoketones and diorganyl diselenides (Scheme 1, #2). [13] In 2019, Sakai and coworkers [14] developed a Pd(II)/Cu(II)-catalyzed dichalcogenation (S and Se) of several arenes, including the synthesis of two examples of 1,3-bis(sulfanyl)indolizines and one 1,3-bis(selanyl) indolizine.…”