A reversal of enantioselectivity induced by an achiral catalyst in association with a chiral catalyst was observed during asymmetric autocatalysis. This reversal of enantioselectivity is interpreted as a result of aggregation between the two catalysts, leading to another catalytic species. Both kinetic and enantioselectivity studies exhibit strong nonlinear effects and were shown to be very consistent with the formation of dimeric catalytic species. They brought some quantitative information about the structure and the catalytic properties of the mixed aggregate. This study also brings some new insights in the mechanism of the catalytic addition of dialkylzincs to aldehydes.