Benzaldehyde photoredox heteroarylates amides and ethers
Household CFL light plus benzaldehyde and APS couples heteroarene C–H bonds to amide/ether α-C–H positions without a metal photocatalyst.
Source
Direct α-heteroarylation of amides (α to nitrogen) and ethers through a benzaldehyde-mediated photoredox reaction
What they did
Authors developed a cross-dehydrogenative coupling using benzaldehyde as a photoabsorber, ammonium persulfate as oxidant, and CFL/black-light irradiation, mapping scope on benzothiazoles/quinolines/amides/ethers and probing mechanism with filters, TEMPO, and substituted benzaldehydes.
What they found
Near-UV (≈364 nm) from CFLs drives the reaction; 0.5 equiv benzaldehyde can suffice (90%); gram-scale 85% isolated yield; formamide carbonyl C–H and N-alkyl C–H both react (e.g. 88% with 8:1 carbonyl selectivity for N-methylformamide).
The limits
What it doesn't show
Partners must be used in large excess, and the method is not a catalytic closed photoredox cycle with a recylable Ir/Ru dye.
Key terms
- CDC
- Cross-dehydrogenative coupling joining two C–H positions with an oxidant.
- Photoredox
- Light-driven single-electron transfer that generates radicals under mild conditions.
- APS
- Ammonium persulfate, the stoichiometric oxidant whose decomposition is enhanced by amides and photoexcited benzaldehyde.
- CFL
- Compact fluorescent lamp used as a household visible/near-UV source.
- α-heteroarylation
- Attachment of a heteroarene to the carbon adjacent to N or O.
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Common questions
Is a metal photocatalyst required?
No—the reaction is metal-free with benzaldehyde as mediator.
What light is essential?
Near-UV from the CFL (~364 nm); darkness gives no reaction.
Gram-scale yield?
85% isolated.
What does TEMPO do?
Inhibits the reaction, supporting radicals.
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