However, substrate scope remains limited, and diisopropylzinc remains the only viable alkylating agent leading to asymmetric amplification. Soai has also demonstrated a variety of ways to initiate and direct product enantiomeric excess in this reaction, including exposure to circularly polarized light, by inorganic chiral materials such as quartz, and by the isotope chirality of an initiator molecule. All of these studies reveal that the Soai reaction requires only an extremely small chiral directing force to effect both symmetry breaking and subsequent asymmetric amplification.