Iodine‐DMSO‐Promoted Oxygenation of Indoles: Synthesis of Isatin and Isoindigo

Abstract

Oxygenation/oxidative self-coupling of indole are performed to obtain isatin and isoindigo in the absence of metal catalysts. Iodine-DMSO is used to synthesize isatin whereas Iodine-DMSO-K 2 S 2 O 8 combination is used for isoindigo synthesis directly from indole in a single step. Though several methods are known for isatin synthesis from indole, most of them use large quantity of oxidants or metal catalyzed. Moreover, the primary existing process for the synthesis of isoindigo is the condensation of isatin and oxindole in the presence of an acid catalyst. But this method provides isoindigo derivatives directly from indoles. A plausible mechanism is also proposed based on the various control experiments which indicate that both the reactions proceed via radical route. It is also observed that oxygen atoms of isatin and isoindigo come from water molecule and DMSO.

DBU-Mediated Dimerization: Facile Access to 9,9′-Bifluorenylidenes and Isoindigos

“…General procedure for the synthesis of substrate 1 2.1 General procedure 1 for the synthesis of 9H-fluoren-9-one 9H-fluoren-9-one was synthesized according to the previous report. 1 20.0 mmol) and KI (0.664 g, 4.00 mmol) were mixed in acetonitrile (60 mL).…”

“…On the basis of a literature search, there are a vast number of reported synthetic protocols to construct isoindigos, for example, acid-catalyzed condensation of isatins with oxindoles, 12 gold-catalyzed dimerization of 3-diazooxindoles, 13 palladium-catalyzed cyclization, 14 dimerization of oxindoles using thionyl chloride (SOCl 2 ) 15 or N -chlorosulfenylsuccinimide, 16 sodium iodide promoted dimerization of oxindoles, 17 visible-light-promoted, iodine-mediated dimerization of 3-diazooxindoles, 18 iron-catalyzed dimerization of isatins, 19 and dimerization of indoles promoted by a combination of I 2 /DMSO/K 2 S 2 O 8 . 20…”

“…On the basis of a literature search, there are a vast number of reported synthetic protocols to construct isoindigos, for example, acid-catalyzed condensation of isatins with oxindoles, 12 gold-catalyzed dimerization of 3-diazooxindoles, 13 palladium-catalyzed cyclization, 14 dimerization of oxindoles using thionyl chloride (SOCl 2 ) 15 or N-chlorosulfenylsuccinimide, 16 sodium iodide promoted dimerization of oxindoles, 17 visible-light-promoted, iodine-mediated dimerization of 3-diazooxindoles, 18 iron-catalyzed dimerization of isatins, 19 and dimerization of indoles promoted by a combination of I 2 /DMSO/K 2 S 2 O 8 . 20 Recently, we disclosed the dimerization of 3-chlorooxindoles by employing potassium ethyl xanthate for the synthesis of a range of isoindigos in yields of 52-89%. 21 To expand the synthetic utility of the present strategy, we realized that 3-chlorooxindoles might be suitable substrates for dimerization into isoindigos under the conditions developed herein (DBU, DMSO, rt, 2 h).…”

Catalyst‐Free Regioselective C3−H Benzoxylation of 1H‐Indoles with Benzoyl Peroxide

“… [10–13] Recently Lombardi et al reported an efficient Mn‐containing artificial enzyme promoted indole oxidation selectively at 3‐position [14] . P. K. Baruah reported I 2 ‐DMSO promoted oxygenation of Indoles to directly obtain Isatin and IsoIndigo [15] . Pd catalyzed [16–19] and transition‐metal‐free [20–22] acetoxylation of substituted indoles with diacetoxy iodobenzene as external oxidant have been studied.…”

“…[14] P. K. Baruah reported I 2 -DMSO promoted oxygenation of Indoles to directly obtain Isatin and IsoIndigo. [15] Pd catalyzed [16][17][18][19] and transition-metal-free [20][21][22] acetoxylation of substituted indoles with diacetoxy iodobenzene as external oxidant have been studied.…”