The Role of Potassium Cation in the Favorskii Ethynylation of Acetone: Effekt of Dibenzo-18-crown-6

Macrocyclic polyether dibenzo-18-crown-6 possessing a specific affinity for potassium cation inhibits ethynylation of acetone with acetylene in the presence of KOH according to Favorskii. The inhibition becomes stronger in the presence of the complex dibenzo-18-crown-6 ? KOH ? MeOH as catalyst (both in excess acetone and in DMSO). The effect does not originate from deactivation of acetone, for its aldol-like condensation is accelerated in the presence of both dibenzo-18-crown-6 and its complex (the selectivity of ethynylation sharply falls down). Thus, apart from the high basicity of the medium, activation of acetylene due to complex formation with potassium cation plays an important role in the Favorskii ethynylation of ketones.