For the Curtin-Hammett principle to be applicable, the rate of isomerization should be faster than the subsequent stereodetermining step. In such a scenario, the diastereomeric composition of the starting material should have no effect on the observed selectivity of the product. As previously indicated (Scheme 3), such behavior was observed under conditions C2, but not for C1. To examine this discrepancy in more detail, both starting material diastereomers (E/Z)-1a, and a 50:50 mixture thereof was subjected to both optimized conditions and the diastereoselectivity for the formation of product 3aa was determined (Table ). Notably, the product selectivity was significantly affected by the geometry of the starting material under conditions C1. Thus, a pronounced drop in the selectivity of 3aa from 99:1 Z/E starting with (Z)-1a to only 79:21 Z/E with (E)-1a was observed (entries 1-3). A potential mechanistic rationale could be that the isomerization barrier is closer in energy to the subsequent stereodetermining step (approaching a "kinetic quench" scenario) for this set of conditions. In other words, (Z)-selectivity is favored in the stereodetermining step (due to the choice of ligand) but the rate of isomerization is too slow resulting in significant formation of (E)-3aa. In stark contrast, the same selectivity was observed under conditions C2 regardless of the Z/E-ratio of the starting material (entries 4-6). This behavior is consistent with typical Curtin-Hammett behavior, which is presumably caused by a lower energy barrier of the isomerization than the stereodetermining step. To rationalize the observed behavior and selectivity of this transformation, a combination of mechanistic experiments and density functional theory (DFT) calculations was employed.