A convenient and efficient iron-catalyzed nucleophilic addition of simple alkenes to isochroman acetals has been established for the synthesis of 1-alkenyl isochromans. In the presence of 5–20 mol % iron(III) p-toluenesulfonate, the alkenyl functionalized isochromans were prepared in moderate to excellent yields. This transformation provides a novel methodology for the synthesis of 1-alkenyl isochromans from simple alkenes and isochroman acetals.