Study On Uv Light-mediated Drcarboxylative Cross-coupling Reaction Of Aryl Acetic Acids

The formation of C-C bond reaction is a basic reaction in organic synthesis,therefore,a variety of methods synthesis of C-C bond including Friedel-Crafts alkylation,condensation reaction,coupling reaction,and most importantly,transition metal-catalyzed C-C bond cross-coupling reactions.Among them,however,most general strategies require Lewis acids,high temperature,extra driving forces and metal catalysts that are usually expensive,toxic,difficult to deal with and environmental unfriendly.Diarylmethane compounds are momentous chemical raw materials and intermediates for organic synthesis,and they are also important structural units of pharmaceutically active molecules,and complex natural products.We realized a photochemically decarboxylative cross-coupling of aryl acetic acids with 1,4-dicyanobenzene(1,4-DCB)to obtain a series of diarylmethane derivatives in moderate to good yields under UV light irradiation.In comparison with the traditional cross-coupling reactions,the starting material,carboxylic acids are cheap and easy to obtain and CO2 is the theoretical by-product which is non-polluting and easily separated from the reaction system.In addition,photochemistry has its unique advantages,such as environmentally friendly,simple manipulation,mild reaction conditions.Herein,a series of aryl acetic acids were prepared to investigate the scope of the reaction.The carboxylic acids with electron-donating groups on the aromatic ring are suitable for the synthesis strategy.However,it is usually difficult for the reaction to take place when an electron-withdrawing group on the aromatic ring.Detected by GC-MS,a control experiment by reaction with TEMPO(2,2,6,6-tetramethyl piperidine)for free radicals capture was conducted and then a possible reaction mechanism was proposed,aryl acetic acids underwent a single electron transfer with 1,4-DCB,then took off carbon dioxide and eventually coupled to obtain diarylmethane compounds.Furthermore,decarboxylative couplings of aryl acetic acids with isocyanates and olefins were also developed.A series of corresponding acetophenone amides and terminal olefins products have been obtained with good yields.