Recent Advances in Visible Light‐induced Asymmetric Transformations of Carbonyl Compounds into Chiral Alcohols

Abstract

Visible light‐induced photocatalysis has been widely investigated, which offers exciting opportunities to build new catalytic platforms that are unattainable under ground state conditions. Asymmetric photocatalysis has been a longstanding challenge due to the high reactivity of photogenerated intermediates leading to strong background reaction. Carbonyl group is an important fundamental scaffold in organic synthesis. The photocatalytic asymmetric transformations of carbonyl compounds for synthesizing enantioenriched secondary and tertiary alcohols are of significant value but remain problematic. Even so, a series of intriguing works concerning this topic have been reported in recent year. This review summarizes the advances in this area, mainly dividing into single and synergetic catalyst systems, and the mechanism of each reaction is discussed.

Asymmetric Cross-Coupling of Aldehydes with Diverse Carbonyl or Iminyl Compounds by Photoredox-Mediated Cobalt Catalysis

“…It is noteworthy that this reaction deviates from the previously discussed CO/CN cross-coupling process by not requiring an external photosensitizer. This peculiarity could be attributed to the inherent photoactivity of aryl ketones, the potential contribution of the Hantzsch ester, or the photoreactive nature of specific cobalt species employed . For a comprehensive analysis of the UV–vis absorption spectra for each component within the context of this reaction, refer to the Supporting Information.…”

Catalytic Asymmetric Dearomative [2 + 2] Photocycloaddition/Ring-Expansion Sequence of Indoles with Diversified Alkenes

“…By absorbing environmentally friendly solar energy, excited-state aromatic compounds can undergo thermodynamically and kinetically favored dearomatization reactions under mild reaction conditions. This approach is especially effective when coupled with inert feedstocks, such as simple alkenes, which are unreactive via traditional synthetic methods. , Although dearomatization through photocatalytic strategy has constantly received intensive research interests, the catalytic asymmetric versions remain sluggish due to strong undesired racemic background reaction involving highly reactive excited state intermediates . To the best of our knowledge, only a few cases of visible light-induced CADA reactions were realized via photocycloadditions with alkenes, enabling versatile and straightforward access to chiral polycyclic compounds.…”

Quinone-Initiated Photocatalytic Enantioselective Giese Radical Addition with Ethers, Thioethers, Amines, and Alkanes

“…Asymmetric Giese radical addition, which invloves trapping carbon-centered radicals with electron-deficient alkenes, is one of the most effective strategies to construct chiral C–C bonds. − With the rapid development of visible-light-induced photocatalytic transformations in recent years, − photoredox-mediated asymmetric Giese reactions have been greatly established (Scheme a, left) . In most cases, redox-active radical precursors that possess a redox auxiliary, such as amine derivatives, − Hantzsch esters, − Barton esters, − trifluoroborates, alkyl halides, and others, − are used in order to readily generate carbon-centered radicals upon the photoinduced single electron transfer (SET) process.…”