Photo-NHC Catalysis: Accessing Ketone Photochemistry with Carboxylic Acid Derivatives
M. N. Hopkinson,* A. Mavroskoufis – 2020
Excitation of carbonyl groups is one of the most widely employed activation modes in photochemistry. Many synthetically important transformations, however, are successful only with aldehydes and ketones while substrates at the carboxylic acid oxidation level remain underrepresented. We have developed a conceptually novel strategy for enabling “ketone-like” photochemistry with carboxylic acid derivatives that employs an N-heterocyclic carbene (NHC) organocatalyst. Using this “Photo-NHC” catalysis approach, a proof-of-concept photoenolization/Diels-Alder (PEDA) reaction between acid fluorides and trifluoroacetophenones was developed. Stoichiometric studies and TD-DFT calculations supported a mechanistic scenario where the NHC influences the absorption wavelength and inherent photochemical reactivity of the carbonyl group during the catalytic cycle.