Designing an Apparently Orbital-Symmetry-Forbidden [3s,5s]-Sigmatropic Shift through Transition-State Complexation and Stereoelectronic Effects

The [3s,5s]-sigmatropic shift is an example of an orbital-symmetry forbidden pericyclic reaction that is outcompeted by the allowed [3s,3s]-sigmatropic shift. Density functional theory calculations are used to show that Pd^II-complexed systems with strategically placed substituents engaging in key stereoelectronic effects can select for the [3s,5s] process, thereby outcompeting both orbital-symmetry-allowed [3s,3s]- and [3s,5a]-shifts.