Direct oxidative dearomatization of indoles: access to structurally diverse 2,2-disubstituted indolin-3-ones

Abstract

Described is an efficient oxidative dearomatization of indoles with TEMPO oxoammonium salt and a broad range of nucleophiles.

Oxidative Dearomative Cross-Dehydrogenative Coupling of Indoles with Diverse C-H Nucleophiles: Efficient Approach to 2,2-Disubstituted Indolin-3-ones

“…reactions focus on the construction of di-or trimerization of indoles [50,[77][78][79][80], and the reactions of indoles with dissimilar C-H nucleophiles are considerably rare [81][82][83]. Recently, we reported an efficient oxidative dearomatization reaction of indoles [84,85]. Encouraged by these results, we envisioned that oxidative dearomatization of indoles with C-H nucleophiles could be achieved under suitable conditions.…”

Hypoiodite-Catalyzed Chemoselective Tandem Oxidation of Homotryptamines to Peroxy- and Epoxytetrahydropyridoindolenines

“…Due to the dual role of TBHP, 3 equiv of TBHP should be required to complete the two-step reaction sequence 4 to 5 (i.e., 2 equiv for oxidative transformation as an oxidant and 1 equiv as a peroxide source), and notably, an excellent productive usage ratio (∼96%) of TBHP was observed under our mild conditions (Scheme a). On the other hand, in the presence of TEMPO + , which would be generated in situ from the oxidation of TEMPO with hypoiodite species, electrophilic addition to 7 at the C-3 position might proceed preferentially to give aminooxyindolenine 11 . Elimination of TEMPOH might proceed to give 3-alkylideneindolenine 12 as an unstable and highly reactive intermediate, which might then react with TBHP to give epoxyindolenine 6 .…”

Organocatalytic Asymmetric Dearomative Oxyalkylation of Indoles Enables Access to C2-Quaternary Indolin-3-ones

“…Based on the aforementioned observations, a plausible mechanism was depicted in Scheme . Initially, an electron donor–acceptor complex 9 was formed directly from 1a and TEMPO oxoammonium and subsequently converted into oxindol-1-ium 10 through an electron-transfer process . The highly reactive intermediate 10 could directly react with 2a in the presence of catalyst and additive with good diastereoselectivity especially to 2-alkylindoles and was also readily captured by H 2 O to return the hemiaminal intermediate 6 to facilitate the oxidation process .…”