Synthesis of Chromones via an Intramolecular Hydroacylation

Significance

Reported is an N-heterocyclic carbene catalyzed synthesis of chromones via an intramolecular hydroacylation of activated alkynes. Several NHCs were tested in combination with different bases leading to the optimized conditions shown in the scheme. From tabular data, it appears that optimization of catalyst loading was not investigated. The substrate scope was well studied and yields are generally good. An alkyne bearing an activating EWG is required in order to avoid the formation of intermolecular benzoin products instead of the desired hydroacylation. A plausible reaction mechanism was proposed. Additionally, alkyne tethers with other EWGs (Ac, COt-Bu, COPh, COBn) were shown to participate in the ­reaction.