Experimental study demonstrates catalytic acyl radical addition from aldehydes to alkynes under blue light, highlighting divergent access to pyrroles and carbocyclic ketones.
Key Points
To develop a photoredox and pyridine N-oxide catalytic platform that generates acyl radicals directly from aldehydes for the divergent synthesis of pyrroles, cyclopentanones, and indanones.
Irradiated mixtures of aldehydes, alkynes, and catalyst combinations of photoredox catalysts and pyridine N-oxide under blue LED light.
Conducted sequential acyl radical addition and Paal–Knorr condensation with primary aliphatic aldehydes and amines, as well as formal [3 + 2] cyclizations with branched or aryl aldehydes.
Investigated the catalytic mechanism using radical trapping experiments, fluorescence quenching, and electrochemical analysis.
Primary aliphatic aldehydes yielded densely functionalized pyrroles through coupled acyl radical addition and condensation with amines.
Branched aliphatic aldehydes selectively formed substituted cyclopentanones, while aryl aldehydes engaged an additional pathway yielding indanones.
Mechanistic assays confirmed that light-driven oxidation of pyridine N-oxide produces an active N-oxy radical that selectively abstracts aldehydic C–H bonds to generate acyl radicals.