Visible‐Light Photocatalysis: Does It Make a Difference in Organic Synthesis?

Abstract

Visible-light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. Photocatalytic variants have been reported for many important transformations, such as cross-coupling reactions, α-amino functionalizations, cycloadditions, ATRA reactions, or fluorinations. To help chemists select photocatalytic methods for their synthesis, we compare in this Review classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed under milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, such as air, oxygen, or amines. Does visible-light photocatalysis make a difference in organic synthesis? The prospect of shuttling electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible-light-absorbing photocatalyst holds the promise to improve current procedures in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown, especially by merging photocatalysis with organo- or metal catalysis.

Solvent Dependent Divergent Reactivity of Electron‐Rich Dienones with and without Visible Light: Access to Cyclopropanated Furans and Butenolides

“…1 General procedure for the synthesis of butenolide derivatives (+ /À )-3. 1 General procedure for the synthesis of butenolide derivatives (+ /À )-3.…”

“…1 3,160.0,147.6,135.7,129.5,128.8,128.5 (2 CH),114.9 (2 CH),113.5,90.3,69.7 (CH 2 ), 25.2, 22.6 (CH 2 ), 11.6, 10.6 ppm; IR (KBr):ñ max = 1749, 1600,1509,1252,1173,1051,976,959 General procedure for the synthesis of amidation products (+ /À )-4. 1 3,160.0,147.6,135.7,129.5,128.8,128.5 (2 CH),114.9 (2 CH),113.5,90.3,69.7 (CH 2 ), 25.2, 22.6 (CH 2 ), 11.6, 10.6 ppm; IR (KBr):ñ max = 1749, 1600,1509,1252,1173,1051,976,959 General procedure for the synthesis of amidation products (+ /À )-4.…”

“…[1] In this context, several external PC-free synthetic methods have been developed recently by utilizing either the photochemical activity of electron donor-acceptor complexes (EDA), [2] or the in situ formed chiral enamines, [3] substrates of a chemical reaction as a photosensitizer. [1] In this context, several external PC-free synthetic methods have been developed recently by utilizing either the photochemical activity of electron donor-acceptor complexes (EDA), [2] or the in situ formed chiral enamines, [3] substrates of a chemical reaction as a photosensitizer.…”

Sichtbares Licht ermöglicht Ruthenium‐katalysierte meta‐C‐H‐Alkylierung bei Raumtemperatur

“…In den letzten Jahren haben sich lichtinduzierte C-H-Funktionalisierungen zu einem verlässlichen und vielseitigen Hilfsmittel der organischen Synthese entwickelt, [14] sowohl im Kontext klassischer ortho-Funktionalisierungen als auch bei der Verwendung von elektronisch begünstigten Heteroarenen. [15] Im Rahmen unseres Forschungsprogramms zu metallaphotoredox-katalysierten C-H-Funktionalisierung [16] haben wir jetzt die bisher unverwirklichte,d urch sichtbares Licht induzierte meta-C-H-Alkylierung bei Raumtemperatur Abbildung 1.…”

Enhancing Temporal Control and Enabling Chain‐End Modification in Photoregulated Cationic Polymerizations by Using Iridium‐Based Catalysts

“…[13] Theb alance required for these two steps leads to large differences in the temporal control observed in these polymerizations when small changes are made to the catalyst structure.F or example,t riphenylpyrylium tetrafluoroborate (1a)g ives fast polymerization but poor temporal control owing to the high number of monomer additions per photon absorbed (approx. [15,16] Moreover,m odification of the ligand structure in these complexes permits precise tuning of both the excited state and ground state redox potentials,a llowing us to predictably control chain-end oxidation and recapping (Figure 1c,s teps Ia nd II). Its highly oxidizing excited state potential (E* =+2.55 Vv s. SCE) gives fast chain-end oxidation;h owever,t he ground-state potential (E 1/2 = À0.31 Vv s. SCE) is too weakly reducing to enable facile recapping of the propagating cation, leading to as ystem that has control over only initiation and not chain growth.…”