The Effect of the Catalyst on the Selectivity of the Heterogeneous 1,4-addition of Organomagnesium Compounds to Chalcone
The conjugate addition in the presence of a catalytic amount of copper is a widely used method for the formation of a C-C bond. However, mostly homogeneous catalysts and/or homogeneous ligands are used in these type of reactions. Previously we reported the heterogeneous catalytic 1,4-addition of organomagnesium compounds to chalcones in the presence of Cu(II) on 4Å molecular sieve support. In this study various heterogeneous supported catalysts were tested in the 1,4-addition reaction, such as La(III), Ti(IV), In(III), Co(II) and Ni(II) on 4Å molecular sieve support. Using the Ti(IV)-4A the desired products could be obtained in excellent yields and no 1,2-addition by-product could be detected. Therefore the reusability of the catalyst was tested in a second reaction. It was found, that the Ti(IV)-4A cannot be reused in this type of reaction, due to significant loss of selectivity. In the second experiment a considerable amount of the 1,2-addition product was formed. Thus, the Cu(II)-4A is a suitable catalyst for the heterogeneous 1,4-addition of organomagnesium compounds to chalcones, as described in our previous work.