Light-triggered elimination of CO2 and absorption of O2 (artificial breathing reaction) in photolysis of 2-(4-nitrophenyl)-1H-indole derivatives

A new chromophore, 2-(4-nitrophenyl)-1H-indole (NPI), was synthesized as a potential photolabile protecting group. Caged benzoic acids featuring the NPI chromophore were model compounds. Benzoic acid released in moderate yields (~ 40–60%) upon photolysis of caged without any additional chemical reagents. Interestingly, an aldehyde, 1-(5-(1-formyl-1H-indol-2-yl)-2-nitrophenyl)ethyl benzoate, isolated ≈ 20% together with (≈ 40%) acid, 2-(2-(3-(1-(benzoyloxy)ethyl)-4-nitrophenyl)-1H-indol-1-yl)acetic acid. The functional group, CH2COOH, at indole nitrogen transformed into aldehyde CHO, under conditions air. similar photochemical transformation observed 2-(2-(4-nitrophenyl)-1H-indol-1-yl)acetic which benzoate group is not attached nitrophenyl ring. Products analysis, transient absorption spectroscopy, and computational study suggested that intramolecular electron transfer key for elimination CO2 O2 formation aldehyde. artificial breathing-type reaction can apply to transition metal-free oxidation amino mild conditions.