A General Method for Photocatalytic Decarboxylative Hydroxylation of Carboxylic Acids

Abstract

A general and practical method for decarboxylative hydroxylation of carboxylic acids was developed through visible light-induced photocatalysis using molecular oxygen as the green oxidant. The addition of NaBH4 to in situ reduce the unstable peroxyl radical intermediate much broadened the substrate scope. Different sp3 carbon-bearing carboxylic acids were successfully employed as substrates, including phenylacetic acid-type substrates, as well as aliphatic carboxylic acids. This transformation worked smoothly on primary, secondary, and tertiary carboxylic acids.

Decarboxylation‐Initiated Intermolecular Carbon‐Heteroatom Bond Formation

“…This transformation was extended to simple primary acids under Ir‐photocatalysis. In this case, the reductant has to be added to the reaction mixture directly at the beginning of the reaction [274] . MacMillan et al.…”

Decarboxylative Hydroxylation of Benzoic Acids

“…Heteroaryl carboxylates, such as isonicotinic carboxylates (6,14) and quinoxa-line-2-carboxylate (15), are also compatible. Functional groups including aryl halides (2,25,27,31), oxidationsensitive aldehydes (10), enolizable ketones (18,28), heterocycles (1,6,7,14,24), sulfonamides (16,17,19,24), amides (22), ether (12,31) and nitriles (3,8,29) are well tolerated. a-Heteroatom (9,12,16,17,22), benzylic (7,11,13,16,23,28,31) and tertiary (9,23) CÀH bonds that are sensitive to HAT processes also did not pose a problem.…”

“…Radical decarboxylation can proceed much faster at activation barriers of about 8-9 kcal mol À1 [2,17] to afford synthetically useful aryl radicals. Aliphatic acids activated through this pathway have been used successfully for radical addition reactions, [18] carbometalation, [19] and radical crossover. [20] However, even with the low barrier for radical aromatic decarboxylation, other reactions such as hydrogen atom abstraction (HAT) and back electron transfer (BET) can be even faster [2] and result in undesired reactivity.…”

Visible Light Induced Reduction and Pinacol Coupling of Aldehydes and Ketones Catalyzed by Core/Shell Quantum Dots

“…The crude product was chromatographed on silica (petroleum ether/EtOAc) to give a colorless liquid, 75% (42.8 mg). 1 H NMR (400 MHz, CDCl 3 ) δ 7.43–7.31 (m, 5H), 4.41 (d, J = 7.1 Hz, 1H), 2.03 (d, J = 12.8 Hz, 1H), 1.91 (s, 1H), 1.86–1.77 (m, 1H), 1.75–1.68 (m, 2H), 1.43–1.40 (m, 1H), 1.30–0.95 (m, 5H).…”