Direct photochemical activation of aliphatic carboxylic acids toward phosphinylation via polarity-reversed Arbuzov process

Direct photochemical activation of carboxylic acids remains elusive because of their negligible absorption in the near-UV and visible regions. Herein, we report a direct activation strategy based on a polarity-reversed Arbuzov process which converts carboxylic acids into photoactive acylphosphine oxides in situ via a formal P(iii) → P(v) rearrangement. Upon 365 nm LED irradiation, the resulting acylphosphine oxides undergo selective Norrish type I cleavage to generate acyl- and phosphinoyl radicals. Harnessing the reactivity of radicals enables an efficient decarboxylative phosphinylation of aliphatic carboxylic acids in good yields with broad scope. Importantly, modulation of the phosphorus linchpin of carboxylic acids redirects the photochemistry from Norrish type II to Norrish type I reactivity, revealing a reactivity switch in the phosphorus-mediated photochemistry.