Cooperative Covalent–Noncovalent Organocatalysis of the Knoevenagel Condensation Based on an Amine and Iodonium Salt Mixture

A synergetic cocatalytic effect provided by an iodonium salt in the base-catalyzed Knoevenagel condensation has been found. The diphenyliodonium triflate serving as the halogen bond-donating Lewis acid provides the higher cocatalytic effect than zinc(II) triflate or triflic acid serving.

Abstract

The experimentally obtained kinetic data has indicated the existence of a synergetic cocatalytic effect provided by an iodonium salt in the base-catalyzed Knoevenagel condensation. The diphenyliodonium triflate serving as the halogen bond-donating Lewis acid provides the higher cocatalytic effect than zinc(II) triflate or triflic acid serving, respectively, as the metal cation-based Lewis acid and Brønsted acid. Such a cocatalytic effect remains the same for a broad scope of carbonyl compounds covering aldehydes featuring electron-withdrawing or electron-donating substituents, as well as ketone involved in the reaction.

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