An I 2 O 5 -mediated decarboxylative and decarbonylative bromination/iodination of electron-rich arenecarboxylic acids and aryl aldehydes by using KBr/KI as the halogen source in water has been developed. This scalable, low-cost, and transition-metal-free halogenation allows convenient access to aryl bromide and iodide under mild conditions. Direct decarboxylative halogenation of carboxylic acid represents one of the most useful strategies for the preparation of halides in synthetic organic chemistry, which is known as the Hunsdiecker reaction. 1-3 To overcome the limitations of the Hunsdiecker reaction, various methods had been developed by Cristol, 4 Barton, 5 and Kochi 6 et al. during the past decades. These pioneering studies along with their modifications provide helpful strategies for the synthesis of alkyl halides, however, most of these systems suffer from previous preparation of carboxylic metal salts and/or esters, overloading of heavy metal salts, and harsh reaction conditions. Very recently, Li and co-workers reported a very efficient silver(I)-catalyzed decarboxylative chlorination and fluorination of aliphatic carboxylic acids. 7 However, aryl carboxylic acids gave no desired products in this system. In 2011, Gandelman and co-workers developed an iododecarboxylation of carboxylic acids by using 1,3-diiodo-5,5-dimethylhydantoin under irradiation conditions. 8 Additionally, a decarboxylative halogenation of electron-rich aryl carboxylic acids by using hypervalent iodine(III)-LiX in fluoroalcohol media was explored by Miki et al. 9 Although these transition-metal-free Hunsdiecker reactions have made the decarboxylative halogenation easier than ever before, challenging problems such as using relatively high-cost halogen sources and oxidant, requirement of fluoroalcohol as the effective medium, and difficulty of large-scale production remain to be addressed so far. To address these challenges, we began to reason that single-electron oxidation of simple halogen anion (e.g., Br -, I -) by a low-cost and nonmetal inorganic oxidant would lead to efficient decarboxylative halogenation of carboxylic acids. The key problem of this strategy lies in finding a proper single-electron oxidant. As our continuous studies on exploring green oxidation systems using more safe and environmentally benign oxidants such as molecular oxygen, HIO 3 (iodic acid, IA), and its anhydride I 2 O 5 (iodine pentoxide, IP), we find that IA and IP can act as safe and reliable single-electron oxidative surrogates for organic hypervalent iodines in several cases. 10 Although IA and IP are very rarely employed in organic synthesis, 11 they are extensively applied in industry due to their particular stability even under high temperature. 12 In order to realize a transition-metal-free decarboxylative halogenation, we hypothesize that oxidation of KBr/KI by IA and/or IP would lead to an efficient Hunsdiecker reaction. Fortunately, we successfully accomplished a safe, green, and scalable decarboxylative bromination and iodination of electron-...
