Isonicotinate Ester Catalyzed Decarboxylative Borylation of (Hetero)Aryl and Alkenyl Carboxylic Acids through N-Hydroxyphthalimide Esters

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Abstract
Decarboxylative borylation of aryl and alkenyl carboxylic acids with bis(pinacolato)diboron was achieved through N-hydroxyphthalimide esters using tert-butyl isonicotinate as a catalyst under base-free conditions. A variety of aryl carboxylic acids possessing different functional groups and electronic properties can be smoothly converted to aryl boronate esters, including those that are difficult to decarboxylate under transition-metal catalysis, offering a new method enabling use of carboxylic acid as building blocks in organic synthesis. Mechanistic analysis suggests the reaction proceeds through coupling of a transient aryl radical generated by radical decarboxylation with a pyridine-stabilized persistent boryl radical. Activation of redox active esters may proceed via an intramolecular single-electron-transfer (SET) process through a pyridine–diboron–phthalimide adduct and accounts for the base-free reaction conditions.
Funding Information
  • Ministry of Education of the People's Republic of China
  • Ministry of Science and Technology of the People's Republic of China (2017YFA0303500)
  • National Natural Science Foundation of China (21325208, 21572212)
  • Chinese Academy of Sciences (XDB20000000)
  • Anhui Province (1604a0702027)

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