The aerobic dehydrogenative lactonization
of alkenoic acids facilitated by a cooperative nonmetallic catalyst
pair is reported. The title procedure relies on the adjusted interplay
of a photoredox and a selenium-π-acid catalyst, which allows
for the regiocontrolled construction of five- and six-membered lactone
rings in yields of up to 96%. Notable features of this method are
pronounced efficiency and practicality, good functional group tolerance,
and high sustainability, since ambient air and visible light are adequate
for the clean conversion of alkenoic acids into their respective lactones.
The title method has been used as a case study to elucidate the general
mechanistic aspects of the dual selenium-π-acid/photoredox catalysis.
On the basis of NMR spectroscopic, mass spectrometric, and computational
investigations, a more detailed picture of the catalytic cycle is
drawn and the potential role of trimeric selenonium cations as catalytically
relevant species is discussed.