Biomimetic Brønsted Acid-Catalyzed Carbonyl-Olefin Metathesis Enabled by Hydrogen Bonding Networks

Synthetic chemists have learned to mimic nature in using hydrogen bonds and other weak interactions to dictate the spatial arrangement of reaction substrates and to stabilize transition states to enable highly efficient and selective reactions. The activation of a catalyst molecule itself by hydrogen bonding networks, in order to control its catalytic activity to achieve desired reaction outcomes is much less explored in organic synthesis, despite being a common strategy in nature. Herein, we show our investigation into this underexplored area by studying the promotion of carbonyl-olefin metathesis reactions by hydrogen bonding-assisted Bronsted acid catalysis. The carbonyl-olefin metathesis reaction has recently emerged as a powerful synthetic tool for functional group interconversion of carbonyls and alkenes. However, the application of Bronsted acid catalysts in carbonyl-olefin metathesis reaction, especially in homogeneous conditions, remains scarce and poorly understood. In this work, we report the use of hexafluoroisopropanol solvent in combination with para-toluenesulfonic acid to efficiently catalyze carbonyl-olefin metathesis reactions. Our experimental and computational mechanistic studies reveal not only an interesting role of HFIP solvent in assisting this Bronsted acid catalyzed reaction but also insightful knowledge about the current limitations of the carbonyl-olefin metathesis reaction.