Unlocking the Aromatic Cope Rearrangement with Gold(I) Catalysis

Aromatic Cope Rearrangement (ArCopeR) is a highly challenging chemical reaction under thermal conditions, primarily attributed to the loss of aromaticity during the initial [3,3]-sigmatropic step of the process. Such a rare transformation typically requires high temperatures and specially engineered 1,5-hexadiene scaffolds, making it impractical for the straightforward synthesis of molecules. Here, we demonstrated that gold(I) catalysts significantly lower the energetic barriers associated with ArCopeR, enabling the reaction to be carried out at low temperatures (rt to 70 °C) in dichloroethane or hexafluoroisopropanol with high yields. Specifically, phosphine gold(I) complex ((p-CF3Ph)3PAuOTf) permits for the diastereoselective and divergent aromatic Cope rearrangement from various α-allyl-α′-heteroaromatic γ-lactone or malonate derivatives, while N-heterocyclic carbene gold(I) (IPrAuNTf2) allows the selective dearomatization reaction. Extended quantum-mechanics calculations, consistent with experimental observations, reveal that (i) an interweaved transformation occurs instead of the expected ArCope cascade made of formal [3,3]-sigmatropic rearrangement and [1,3]H-shift steps and that (ii) van der Waals interactions between the catalyst and substrate contribute to the interrupted ArCope process leading to dearomatize products. This study presents the first catalytic and synthetically useful protocol to promote ArCopeR under mild conditions.