Visible Light-Driven Decarboxylative Alkylation of Aldehydes via Electron Donor–Acceptor Complexes of Active Esters

Abstract

There are some synthesis methods from widely available aldehydes to the corresponding ketones, however, they involved in multistep reactions with Grignard’s reagents or transition metal catalysts. In this paper, we have developed photocatalyst-free and visible light-driven decarboxylative alkylation of pyridinaldehydes. The photochemical reactions are initiated via photoinduced single electron transfer from triethylamine to N-hydroxyphthalimide esters in electron donor–acceptor complexes. This photochemical method can achieve to translate 15 pyridinaldehydes and 11 2-quinolinaldehydes to the corresponding ketones. Furthermore, this strategy can also achieve two other transformations, disulfanes to aryl sulfides and a styrene sulfone to the alkyl-substituted alkene.

Photocatalytic Ketyl Radical Initiated Cketyl−Csp2/Csp3 Coupling on ZnIn2S4

“…Under the irradiation of blue light (450 nm), ZnIn 2 S 4 is excited to generate holes (h + ) and electrons (e À ). The resulting holes can oxidize TEA to a radical cation, [21] which acts as a HAT reagent for the following steps. The excited electrons, coupled with protons, are utilized to transform 1 a to a neutral ketyl radical (m1) via a PCET process.…”

“…This step is a intermolecular C ketyl À C sp2 coupling reaction and yields another radical intermediate m4. This new carbon-centered radical m4 can undergo two TEA-mediated HAT pathways [21] to regenerate the C=C double bond and produce either the experimentally observed product 5 a or another side-product 5 a', depending on which hydrogen is abstracted. In contrast, Path 2 demands a direct HAT process from cyclohexene to yield a carbon-centered radical (m5) at its allylic position.…”

Photoinduced Alkenylation of Alkenyl Sulfones with EDA Complexes between NHPI Esters and HE

“…This strategy is intrinsically different from photoredox catalysis, and it does not rely on an exogenous photocatalyst [17g] . NHPI ester is easily prepared from alkyl carboxylic acid [17a,18] . Due to its electron‐deficient nature, NHPI ester could associate with suitable electron donor to form an EDA complex, and then gives alkyl radicals for subsequent transformation under visible light irradiation.…”