Excited‐State 2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ*) Initiated Organic Synthetic Transformations under Visible‐Light Irradiation

Abstract

Dedicated to Prof. Shunichi Fukuzumi on the occasion of his 70 th birthday.The one-electron oxidizing capacity of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) improves significantly by visible-light excitation. The exited-state DDQ (DDQ*) even converts benzene, fluoroarenes, heteroarenes, benzyls, and olefins into their corresponding radical cations as well as chloride and other anions into their radicals. These reactive intermediates have been utilized for the generation of CÀ C and CÀ X (N, O, or Cl) bonds in the synthesis of valuable organic compounds and natural products. This mini review provides an overview of such DDQ*-initiated organic transformations with their scope and limitations and discusses the proposed reactions mechanisms.

Organophotoredox Catalyzed Stereoselective Nitration of Olefins with tert‐Butyl Nitrite under Air

“…However, the substantial luminescence quenching effect displayed by the styrene derivative (Figure 1) and comparatively diminished reactivity of the electron‐deficient double‐bonds towards the nitration reaction advocate for an electron transfer photooxidation of the olefins (Path A) as the major pathway. Finally, regeneration of the DDQ photocatalyst proceeds through aerial oxidation with the assistance of TBN [11a] . Presumably, in both pathways, the preferential E ‐stereoselectivity observed may be due to a higher stability of the E ‐isomer over that of the Z olefin.…”

“…We initiated the investigation by analyzing the optoelectronic properties of the organo‐photocatalyst DDQ and the redox potential of the reactant olefins. Although the synthetic utility of quinone derivatives as photocatalyst is underexplored, recent studies revealed that DDQ can participate in the photoinduced electron transfer process and can be a superior photo‐oxidant [11a] . Photo‐excited DDQ* possesses high reduction potential [ E 1/2 (DDQ*/DDQ .− )=3.18 V vs SCE] with a prolonged triplet excited‐state lifetime of 2.4 ms.…”

Synthetic Molecular Photoelectrochemistry: New Frontiers in Synthetic Applications, Mechanistic Insights and Scalability

“…The second subcategory of e‐PRC, dubbed “recycling e‐PRC”, involves the turnover of a photocatalyst that is a known photoredox catalyst (PRCat) in PRC, and that is a colored species in its ground, neutral state. Figure 19 depicts the structures of PRCats used in recycling e‐PRC; their photophysical properties are thoroughly detailed elsewhere [2c,e, 38, 55] . In recycling e‐PRC, the available “redox window” is no wider than it is for PEC.…”

“…DDQ as an eutral photocatalyst is ap owerful oxidant in its long-lived triplet excited state (+ 3.18 Vv s. SCE). [38] Despite its absorbance maxima at % 400 nm, DDQ is successfully photoexcited with longer wavelength blue (455 nm) light. Prior to any contemporary reports of recycling e-PRC,K çnigsg roup achieved the photocatalytic oxidation of electron-deficient arenes by 3 DDQ*i nt he presence of tert-butyl nitrite and molecular oxygen, [39] which was reviewed previously.…”

Synthetische molekulare Photoelektrochemie: neue synthetische Anwendungen, mechanistische Einblicke und Möglichkeiten zur Skalierung

“…Die zweite Unterkategorie von e‐PRC, die als “Recycling‐e‐PRC” bezeichnet wird, umfasst den Umsatz eines Photokatalysators, des PRC, dessen neutraler Grundzustand eine farbige Spezies darstellt. Abbildung 19 zeigt die Strukturen von PRC‐Katalysatoren, die bei Recycling e‐PRC verwendet werden; ihre photophysikalischen Eigenschaften werden an anderer Stelle ausführlich beschrieben [2c,e, 38, 55] . Beim Recycling‐e‐PRC ist das verfügbare “Redoxfenster” nicht größer als bei der PRC.…”