The ene reaction of singlet oxygen with the chiral alkene 2-methyl-5-phenyl-2-hexene in solution is not regioselective and exhibits very poor diastereoselectivity (~10% d.e.). Within thionin-supported zeolite Na-Y, significant enhancement of product regioselectivity and diastereoselectivity (up to 54% d.e.) was obtained. Higher diastereoselectivity is found if the reaction occurs at the twix relative to the twin methyl group.