Photochemical Decarboxylative Formylation of Indoles with Aqueous Glyoxylic Acid

Abstract

A direct metal- and oxidant-free photochemical decarboxylative formylation of indoles with 50% aqueous glyoxylic acid proceeds in good to moderate yields.

Key words

photochemistry - indoles - formylation - decarboxylation - transition-metal-free - glyoxylic acid

Publikationsverlauf

Eingereicht: 04. Juni 2022

Angenommen nach Revision: 30. Juni 2022

Artikel online veröffentlicht:
26. Juli 2022

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• 13 1H-Indole-3-carboxaldehyde (3a): Typical ProcedureA 10 mL quartz tube was charged with indole (1a; 0.25 mmol, 1 equiv), 50% aq. glyoxylic acid (2; 0.51 mmol, 2 equiv), and MeCN (6.0 mL), and the solution was irradiated with eight 8 W 254 nm UV lamps in a photochemical reactor at rt for 6 h until the reaction was complete (TLC). The reaction was then quenched with H₂O (5 mL) and the mixture was extracted with EtOAc (3 × 5 mL). The extracts were dried (Na₂SO₄) and concentrated in a rotary evaporator, and the crude product was purified by column chromatography [silica gel, EtOAc–hexane (4:6)] to give a yellow solid; yield: 65%; mp 189–191 °C (Lit.^3a 190–192 °C).¹H NMR (500 MHz, DMSO-d ₆): δ = 12.14 (br s, 1 H), 9.95 (s, 1 H), 8.28 (d, J = 3.1 Hz, 1 H), 8.11 (d, J = 7.6 Hz, 1 H), 7.52 (d, J = 7.9 Hz, 1 H), 7.28–7.21 (m, 2 H). ¹³C{¹H} NMR (125 MHz, DMSO-d ₆): δ = 185.44, 138.90, 137.52, 124.59, 123.93, 122.59, 121.30, 118.64, 112.88