A kinetic model for reaction between pyrimidyl aldehyde (A) and diisopropylzinc (Z) to produce R and S alkanol products may be written for either monomers or dimers as the active catalysts (Scheme 8). The question of whether it is the monomers or the higher order species that serve as the active catalyst -that is, the Noyori vs. Kagan model -was addressed in the early studies of Blackmond and Brown. Because of the similarity in the chemistry of the Soai reaction to that of the asymmetric alkylation of aldehydes studied by Noyori, a reasonable proposal could