Visible-light-enabled denitrative carboxylation of β-nitrostyrenes: a direct photocatalytic approach to cinnamic acids

Abstract

A novel, highly stereoselective synthesis of (E)-cinnamic acids from β-nitrostyrenes and CBr4employing visible light photoredox catalysis has been developed.

Visible Light‐Induced, Metal‐Free Denitrative [3+2] Cycloaddition for Trisubstituted Pyrrole Synthesis

“…The intermediate D follows cyclization and base‐mediated denitration sequence to afford the trisubstituted pyrrole 3 a . It is noteworthy that radical addition on the nitroalkene takes place in Michael fashion unlike usual reactions of nitroalkenes under visible light irradiation owing to the charge stabilizing capacity of the nitro group. This in effect accords high level of regioselectivity to the reaction, affording products as a single regioisomer.…”

“…The radicalc ation A forms 2-azaallenyl radical cation B/B' following ring opening through CÀCb ond cleavage. The radicalc ation B' adds on to the b-position of nitroalkene 2a furnishing intermediate C,w hich oxidizes the reduced photocatalyst and leads to the intermediate species D.T he intermediate D follows cyclization and base-mediated denitration sequence to afford the trisubstituted pyrrole 3a.I ti sn oteworthy that radicala ddition on the nitroalkenet akes place in Michael fashion unlike usual reactions of nitroalkenesu nder visible light irradiation [15][16][17][18] owing to the charge stabilizingc apacity of the nitrog roup. This in effect accords high level of regioselectivity to the reaction, affording products as as ingle regioisomer.…”

“…The strong electron withdrawing nature of the nitro group makes them highly electron deficient alkenes, a suitable substrate for numerous organic reactions such as Michael reaction, Mannich reaction, Baylis–Hillman reaction, Rauhut‐Currier reaction, cycloadditions and metal‐catalyzed coupling reactions . Recently, nitroalkenes have been exploited as the source of alkenyl function in visible light mediated denitrative arylation, trifluoromethylation, carboxylation and alkylation reactions . However, to the best of our knowledge, nitroalkene have never been used as dipolarophiles in visible light mediated cycloaddition reactions.…”

Visible Light Mediated C(sp3)‐H Alkenylation of Cyclic Ethers Enabled by Aryl Ketone

“…Additionally, nitroalkenes are more atomic economic as alkenylation reagent . Thus, β ‐nitrostyrenes have been employed as alkenylation reagents for radical de‐nitrative benzo‐ylation, carboxylation, trifluoromethylation and arylation . However, to the best of our knowledge, nitroalkenes has never been employed in the C(sp 3 )‐H alkenylation of ether mediated by visible light.…”

Natural and Synthetic Derivatives of Hydroxycinnamic Acid Modulating the Pathological Transformation of Amyloidogenic Proteins

“…One successful eco-sustainable example is visible light photoredox catalysis ( Figure 3 ), which implements visible light as a clean and cheap energy source, and CBr 4 in alkaline aqueous solution providing the carboxylic acid moiety. ( E )-4-(2-nitrovinyl)phenol and CBr 4 as coupling partners were thus used for a highly stereoselective synthesis of ( E )- p -coumaric acid in high 83% yield [ 58 ]. New green chemistry approaches have commonly employed water as the main solvent.…”