We report the selective formation of cyclohexenes with a tetrasubstituted double bond, the structural key element of megastigmanes. For this purpose the ZrCl₄-mediated epoxide ring opening of epoxy-geranylacetone was employed. This approach provides a universal entry to the preparation of the members of the megastigmane family, which was exemplified in the asymmetric synthesis of tectoionol B.