Calcium Hydroxyapatites as Efficient Catalysts for the Michael C–C Bond Formation

Abstract

Calcium hydroxyapatites of different compositions and various specific surface areas (SSA) are shown to be efficient catalysts for the Michael reaction involving ethyl 2-oxocyclopentanecarboxylate, methyl 2-oxocyclopentanecarboxylate, ethyl 2-oxocyclohexanecarboxylate, methyl 1-oxoindane-2-carboxylate and ethyl 3-oxo-3-phenylpropanoate with 3-buten-2-one. The reaction without solvent is nearly quantitative and leads to the expected addition products. The catalyst can be easily recovered by filtration. From deuterium labeling experiments, a mechanism based on the basic properties of the calcium hydroxyapatite surfaces is proposed to explain their ability to catalyze the Michael reaction.