Decarboxylative Oxygenation via Photoredox Catalysis

Abstract

The direct conversion of aliphatic carboxylic acids to their dehomologated carbonyl analogues has been accomplished through photocatalytic decarboxylative oxygenation. This transformation is applicable to an array of carboxylic acid motifs, producing ketones, aldehydes, and amides in excellent yields. Preliminary results demonstrate that this methodology is further amenable to aldehyde substrates via in situ oxidation to the corresponding acid and subsequent decarboxylative oxygenation. We have exploited this strategy for the sequential oxidative dehomologation of linear aliphatic chains.

Decarboxylative oxygenation of carboxylic acids with O2via a non-heme manganese catalyst

“…Notably, the primary stearic acid and oleic acid could be oxidized to the corresponding aldehydes; however, low yields, as well as low conversions were observed ( 5i and 5j ). In comparison with Macmillan's work in 2019, 35 this protocol shows a wider substrate scope. Not only can the cyclic aliphatic acids be oxidized selectively, but also long-chain fatty acids, saturated and unsaturated, could be converted, which are usually challenging substrates.…”

“…So far, there have been only three reports, demonstrating the reaction via photoredox catalysis using molecular oxygen (O 2 ) under mild conditions. Two of these require precious Ru or Ir photocatalysts, 34,35 while the third produces a mixture of alcohols and ketones/ aldehydes as the products (Scheme 1a). 36 Other methods have been reported; however, they make use of stoichiometric strong oxidants, e.g.…”

Decarboxylation‐Initiated Intermolecular Carbon‐Heteroatom Bond Formation

“…MacMillan et al. developed an Ir(III)‐based photocatalytic protocol for decarboxylative oxygenations, which is limited to aryl acetic acids as substrates [275] . Photochemical oxygenations are also promoted by earth‐abundant cerium catalysts (Scheme 33B) [276] .…”

A Readily-Reconfigurable Continuous-Stirred Tank Photochemical Reactor Platform

“…10 We wished to demonstrate the capabilities of the optimised reactor design in a biphasic gas-liquid process, and chose MacMillan's photoredox-catalysed decarboxylative oxidation of carboxylic acids. 16 For ease of operation, rather than the final optimised conditions described in that paper we adopted simplified conditions (alternative photocatalyst, no viologen salt additive and use of air rather than oxygen as the source of terminal oxidant). The substrate (1,1-diphenylacetic acid), catalyst and base were co-injected as a homogeneous solution, while air was added via a syringe pump.…”