Photoinduced Cu(II)‐Mediated Decarboxylative Thianthrenation ofAryl and Heteroaryl Carboxylic Acids

Abstract

AbstractGiven that (hetero)aryl carboxylic acids are inexpensive materials available in a great variety from commercial and natural resources or synthesis, the strategies enabling their use as starting materials for preparing fine chemicals are highly sought after. Here we report a photoinduced Cu(II)‐mediated protocol converting (hetero)aryl carboxylic acids into (hetero)aryl thianthrenium salts, high value‐added building blocks that can undergo various subsequent transformations, creating an attractive two‐step pathway for the divergent functionalization of these ubiquitous starting materials. The excellent compatibility of the method is shown by preparing a broad range of sterically and electronically varied (hetero)aryl thianthrenium salts, including derivatives of pharmaceuticals, such as ataluren, celecoxib, flavoxate, probenecid, repaglinide, and tamibarotene. The syntheses of 13 C‐labeled probenecid and bioisosteres of ataluren as well as the unconventional modifications of celecoxib and flavoxate, illustrate the synthetic potential of the strategy. Mechanistic studies are in line with a reaction occurring through a photoinduced ligand‐to‐metal charge transfer (LMCT) of Cu(II)‐arylcarboxylates, enabling radical decarboxylative carbometallation to form arylcopper(II) intermediates that in turn react with thianthrene to form the product. Noteworthy, the susceptibility of aryl thianthrenium salts to photodegradation is overcome by a Cu(I)‐driven salvage loop, which continuously intercepts the transiently formed radicals and regenerates the products.