Pericyclic reactions bypass high-energy reactive intermediates by synchronizing bond formation and bond cleavage. The present work offers two strategies for uncoupling these two processes and converting concerted processes into their "interrupted" versions by combining Au(I) catalysis with electronic and stereoelectronic factors. First, we show how the alignment of the C3-C4 bond with the adjacent π systems can control the reactivity and how the concerted scission of the central σ bond is prevented in the boat conformation. Second, the introduction of a fluorine atom at C3 also interrupts the sigmatropic shift and changes the rate-determining step of the interrupted cascade from the 6-endo-dig nucleophilic attack to the fragmentation of the central C3-C4 bond. Furthermore, this effect strongly depends on the relative orientation of the C-F bond toward the developing cationic center. The equatorial C-F bond has a much greater destabilizing effect on TS2 due to the more efficient through-bond interaction between the acceptor and the cationic π system. In contrast, the axial C-F bond is not aligned with the bridging C-C bonds and does not impose an equally strong deactivating stereoelectronic effect. These differences illustrate that the competition between concerted and interrupted pericyclic pathways can be finely tuned via a combination of structural and electronic effects modulated by conformational equilibria. The combination of Au(I) catalysis and C-F-mediated stereoelectronic gating delays the central bond scission, opening access to the interrupted Cope rearrangements and expanding the scope of this classic reaction to the design of new cascade transformations.

Tandem Au(III)-catalyzed heterocyclization/Nazarov cyclizations leading to substituted carbocycle fused furans are described. An interesting dichotomy of reaction pathways as a function of solvent, confirmed by the isolation and trapping of reaction intermediates, provided a basis for computational studies that supported the experimental findings.

Curtin-Hammett analysis of four alternative mechanisms of the gold(I)-catalyzed [3,3] sigmatropic rearrangement of allenyl vinyl ethers by density functional theory calculations reveals that the lowest energy pathway (cation-accelerated oxonia Claisen rearrangement) originates from the second most stable of the four Au(I)-substrate complexes in which gold(I) coordinates to the lone pair of oxygen. This pathway proceeds via a dissociative transition state where the C-O bond cleavage precedes C1-C6 bond formation. The alternative Au(I) coordination at the vinyl π-system produces a more stable but less reactive complex. The two least stable modes of coordination at the allenyl π-system display reactivity that is intermediate between that of the Au(I)-oxygen and the Au(I)-vinyl ether complexes. The unusual electronic features of the four potential energy surfaces (PESs) associated with the four possible mechanisms were probed with intrinsic reaction coordinate calculations in conjunction with nucleus independent chemical shift (NICS(0)) evaluation of aromaticity of the transient structures. The development of aromatic character along the "6-endo" reaction path is modulated via Au-complexation to the extent where both the cyclic intermediate and the associated fragmentation transition state do not correspond to stationary points at the reaction potential energy surface. This analysis explains why the calculated PES for cyclization promoted by coordination of gold(I) to allenyl moiety lacks a discernible intermediate despite proceeding via a highly asynchronous transition state with characteristics of a stepwise "cyclization-mediated" process. Although reaction barriers can be strongly modified by aryl substituents of varying electronic demand, direct comparison of experimental and computational substituent effects is complicated by formation of Au-complexes with the Lewis-basic sites of the substrates.

The combination of experiments and computations reveals unusual features of stereoselective Rh(I)-catalyzed transformation of propargyl vinyl ethers into (E,Z)-dienals. The first step, the conversion of propargyl vinyl ethers into allene aldehydes, proceeds under homogeneous conditions via a "cyclization-mediated" mechanism initiated by Rh(I) coordination at the alkyne. This path agrees well with the small experimental effects of substituents on the carbinol carbon. The key feature revealed by the computational study is the stereoelectronic effect of the ligand arrangement at the catalytic center. The rearrangement barriers significantly decrease due to the greater transfer of electron density from the catalytic metal center to the CO ligand oriented trans to the alkyne. This effect increases electrophilicity of the metal and lowers the calculated barriers by 9.0 kcal/mol. Subsequent evolution of the catalyst leads to the in situ formation of Rh(I) nanoclusters that catalyze stereoselective tautomerization. The intermediacy of heterogeneous catalysis by nanoclusters was confirmed by mercury poisoning, temperature-dependent sigmoidal kinetic curves, and dynamic light scattering. The combination of experiments and computations suggests that the initially formed allene-aldehyde product assists in the transformation of a homogeneous catalyst (or "a cocktail of catalysts") into nanoclusters, which in turn catalyze and control the stereochemistry of subsequent transformations.

We show how synergy between properly placed acceptor and donor groups allows rational design of interrupted and aborted pericyclic reactions, using the Cope rearrangement as a model process. When placed at C2 and C5 carbons of 1,5-hexadienes, a frustrated Lewis pair made of two complementary groups assures that the C–C bond formation is assisted by the flow of electron density from a donor at C5 into an acceptor at C2 through the formation of the C1–C6 bond. If the electron excess at the accepting group is strongly stabilized by the electronic nature of substituents, the pericyclic transition state can become an energy minimum, leading to a switch from a concerted sigmatropic shift to its aborted or interrupted versions. Depending on the electronic nature of acceptors at C5 and the donor groups at C2, a range of possibilities from concerted to aborted pathways is accessible, including the first example of an aborted Cope rearrangement in the absence of a metal catalyst. Furthermore, the zwitter-ionic strategy stabilizes the usually unfavorable boat TS that can potentially evolve into rarely accessible bicyclohexane products.