Synthesis of Indoline-2,3-diones by Radical Coupling of Indolin-2-ones with tert-Butyl Hydroperoxide

^◊ These authors contributed equally to this work.

Abstract

A novel strategy has been developed for the synthesis of indoline-2,3-diones through a metal-free radical-coupling reaction. Alkyl radicals derived from indolin-2-ones through a radical-transfer reaction combine with the tert-butylhydroperoxy radical readily generated from commercially available tert-butyl hydroperoxide to afford 3-(tert-­butylperoxy)indolin-2-one intermediates that can be further transformed into indoline-2,3-diones under air. This strategy provides a ­simple and efficient route to the construction of a C=O bond without the use of any metal catalyst or base.

Key words

radical coupling - indolinones - oxidation - indolinediones - tert-butyl hydroperoxide

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• 13 Indoline-2,3-diones 3a–l; General Procedure To a Schlenk tube were added the appropriate indolin-2-one 1 (0.3 mmol), t-BuOOH (0.6 mmol), and DCE (2 mL). The mixture was then stirred at 85 °C under air for the indicated time until the starting material was completely consumed (TLC). The resulting mixture was washed with brine (3 × 5 mL), and the aqueous phase was extracted with EtOAc (3 × 10 mL). The combined organic extracts were dried (Na₂SO₄) and concentrated under vacuum to give a crude product that was purified by column chromatography [silica gel, hexane–EtOAc (10:1)]. The products were analyzed by ¹H and ¹³C NMR and MS (see Supporting Information). 1H-Indoline-2,3-dione (3a) Red solid; yield: 0.0357 g (81%); mp 122.8–123.4 °C; ¹H NMR (400 MHz, DMSO-d ₆): δ = 11.07 (s, 1 H), 7.59 (t, J = 8.0 Hz, 1 H), 7.50 (d, J = 7.6 Hz, 1 H), 7.07 (t, J = 7.6 Hz, 1 H), 6.92 (d, J = 8.0 Hz, 1 H). ¹³C NMR (100 MHz, DMSO-d ₆): δ = 184.8, 159.8, 151.2, 138.8, 125.1, 123.2, 118.2, 112.7. LRMS (EI, 70 eV): m/z (%) = 147 (M⁺, 61), 119 (100), 92 (74).
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