Apatites in Aqueous Media: Efficient and Environmentally Friendly Catalyst Systems for the Synthesis of α,β-Unsaturated Esters and 2-amino-chromenes
In this work, we have contributed to environmental protection through the catalytic application of apatites in clean processes for the synthesis of α,β-unsaturated esters and 2-amino-chromenes. Indeed, we have demonstrated for the first time that fluorapatite alone (FAP) and sodium nitrate-doped fluorapatite (Na/FAP) are successfully used as catalysts for the Wittig reaction in aqueous media. The latter catalyst (Na/FAP) is stable and recyclable, enabling α,β-unsaturated esters to be obtained in very good yields in short times and under mild operating conditions, in perfect harmony with green chemistry concepts. In the same approach, we have extended the catalytic scope of (Na/FAP) in water for the synthesis of substituted 2-amino-2-chromenes by reaction with three components, an aromatic aldehyde, malononitrile and 1-naphthol. The yields of the products obtained are high (69-96%). The possibility of recycling this catalyst and the use of water as a green solvent are proving very useful from both a synthetic and environmental point of view.