Soai's breakthrough came when he extended the substrate scope to include pyrimidyl aldehydes (Scheme 6d). In this case, the reaction rate is accelerated by addition of catalytic amounts of its alcohol product, and the autocatalytic product may be obtained after many cycles in very high enantiomeric excess starting from a very low enantiomeric excess in the original catalyst. Since this initial discovery, Soai's group has gone on to demonstrate more efficient amplification with other pyrimidyl aldehydes. Higher degrees of asymmetric amplification are found when R=H is substituted with R = CH3 or C2-X, where X = t Bu, C2Si(CH3)3, or C2(1-adamantyl).