Substrate Photoswitching for Rate Enhancement of a Organocatalytic Cyclization Reaction

Abstract

AbstractIn this article, we report that applying in situ LED‐NMR irradiation with appropriate wavelength resulted in the photoswitching of an α,β‐unsaturated hydrazone C=N double bond configuration. This reaction was previously reported to be the first step in a chiral Brønsted acid‐catalyzed cyclization reaction, where the minor but stable Z‐isomer is the reactive intermediate. By enhancing the rate of the isomerization, we could show that the overall rate of the cyclization could be increased and followed directly by NMR kinetics. Exclusively light with a specific wavelength matching the isomerization process affected the cyclization. The light‐ and acid‐mediated isomerization provide complementary pathways that can be exploited in synthetic applications to increase reaction rates of asymmetric transformations, especially in reactions requiring high loadings of elaborate chiral catalysts.