Intramolecular ene reaction promoted by mixed cogels

The activity and selectivity of SiO2-TiO2, SiO2-ZrO2 and SiO2-Al2O3 mixed cogels, both in the presence and in the absence of copper, have been investigated in the cyclization of citronellal to isopulegol. Although the nature of the catalytic sites is not clear, the very high selectivity of the reaction makes it synthetically attractive.