Photocatalyzed oxidative cleavage of CC bond to carbonyl compounds by a recyclable homogeneous carbon nitride semiconductor/aqueous system

The development of methods based on direct oxidative cleavage of alkynes to carbonyls is an extremely challenging task. In this work, we describe a UV light-driven, potassium/sodium poly(heptazine imide) (K,Na-PHI)-catalyzed protocol for the selective oxidative cleavage of alkynes to acids under an O-2 atmosphere using water as a solvent. Various aromatic alkynes can be selectively cleaved to afford aromatic acids in good to high yield under clean, mild conditions. Mechanistic investigation indicates that the photogenerated hydroxyl radicals in situ act as green oxidation active species. Moreover, this protocol could be further developed as a sequential oxidative cleavage/esterification process for the preparation of aryl esters. Notably, the KNaPHI-II/water catalyst system could be used several times without significant loss of activity.