Knoevenagel, wittig and wittig-horner reactions in the presence of magnesium oxide or zinc oxide.

Alkenes are prepared by Wittig, Knoevenagel and Wittig-Horner reactions in solid-liquid systems, with magnesium oxide or zinc oxide as catalyst. When Wittig-Horner reaction is competitive with Knoevenagel reaction, the catalyst can be modified to give a highly selective reaction ; the addition of dimethylsulfoxide on MgO or heiamethylphosphoric triamide on ZnO gives more efficient catalysts for the Wittig-Homer reaction. The addition of a small amount of HgCl2, or CdCl2, on ZnO gives more efficient catalysts for the Knoevenagel reaction.