TEMPO Oxoammonium Salt Research Articles

Dearomative oxyphosphorylation of indoles enables facile access to 2,2-disubstituted indolin-3-ones.

A highly efficient oxidative dearomatization of indoles with H-phosphorus oxides in the presence of TEMPO oxoammonium salt has been demonstrated. Through the intramolecular oxidative dearomatization of indoles and subsequent intermolecular nucleophilic addition with phosphorus nucleophile, a variety of structurally diverse arylphosphoryl and alkylphosphoryl indolin-3-ones were obtained in good yields with a broad substrate scope and high functional-group compatibility.

Direct Oxidative Dearomatization of Indoles with Aromatic Ketones: Rapid Access to 2,2-Disubstituted Indolin-3-ones

A metal-free oxidative dearomatization of indoles with aromatic ketones mediated by TEMPO oxoammonium salt is described. The dearomatization proceeds smoothly and displays a broad substrate scope with respect to both indoles and aromatic ketones in the presence of H2SO4, affording the corresponding 2,2-disubstituted indolin-3-ones in good yields.

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

A facile and efficient asymmetric dearomative oxyalkylation of indoles with TEMPO oxoammonium salt and a variety of aldehydes and ketones has been described. This metal-free approach provides a straightforward access to C2 quaternary oxindoles in high yields with excellent diastereo- and enantioselectivities under very mild conditions. The reaction goes smoothly even with only 0.1% equivalent catalyst. Moreover, 2-alkylindoles have proven to be suitable substrates for the first time.

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

Described is an efficient oxidative dearomatization of indoles with TEMPO oxoammonium salt and a broad range of nucleophiles. Under very mild conditions, dearomative oxyalkynylation and oxyalkenylation of indoles to structurally diverse 2,2-disubstituted indolin-3-ones were developed for the first time with high atom-economy. In addition, dearomative oxyarylation, oxyallylation, and oxycyanation of indoles were also demonstrated. Mechanism studies indicated that TEMPO oxoammonium salt served as the sole oxidant source through an electron donor-acceptor (EDA) intermediate.

Metal-Free Synthesis of Pyrrolo[1,2-a]quinoxalines Mediated by TEMPO Oxoammonium Salts

We herein describe a novel TEMPO oxoammonium salt initiated Pictet–Spengler reaction of imines, generated in situ from carbonyl compounds and pyrrole- or indole-containing substrates, to afford 4,5-dihydropyrrolo[1,2-a]quinoxalines or 5,6-dihydroindolo[1,2-a]quin­oxalines in good to excellent yields. Moreover, a one-pot synthesis of a biologically important quinoxaline is achieved via a cyclization–dehydrogenation process using one equivalent of the oxoammonium salt.

Direct oxidative C-H alkynylation of N-carbamoyl tetrahydroisoquinolines and dihydroisoquinolines.

An efficient oxidative C-H alkynylation of N-carbamoyl tetrahydroisoquinolines mediated by a TEMPO oxoammonium salt has been established. A variety of electronically varied N-carbamoyl tetrahydroisoquinolines reacted with a range of alkynyl potassium trifluoroborates smoothly under mild metal-free conditions. Dihydroisoquinolines were also suitable components for the reaction. The synthetic applicability of the method for facile access to structurally diverse bioactive molecules was further demonstrated.

In Situ Generated TEMPO Oxoammonium Salt Mediated Tandem Cyclization of β-Oxoamides with Amine Hydrochlorides for the Synthesis of Pyrrolin-4-ones.

A novel in situ generated TEMPO oxoammonium salt mediated one-pot tandem reaction has been developed for the straightforward construction of pyrrolin-4-ones from readily available β-oxoamides with amine hydrochlorides. The reaction tolerates various functional groups and represents a reliable method for the synthesis of highly substituted pyrrolin-4-ones in good yields under mild conditions. Detailed mechanistic studies disclosed that TEMPO oxoammonium salt generated in situ was crucial for the transformation involving the formation of enaminone precursors in situ by condensation of the β-oxoamides with amines, followed by sequential oxidative coupling with β-oxoamides, intramolecular cyclization, and 1,2-alkyl migration steps.

ChemInform Abstract: Iron‐Catalyzed Oxidative Tandem Reactions with TEMPO Oxoammonium Salts: Synthesis of Dihydroquinazolines and Quinolines.

AbstractThis method uses a TEMPO oxoammonium salt (TBF) as a mild and nontoxic oxidant with readily available iron salts as catalysts for the synthesis of the title compounds.

Iron-Catalyzed Oxidative Tandem Reactions with TEMPO Oxoammonium Salts: Synthesis of Dihydroquinazolines and Quinolines

A straightforward iron-catalyzed divergent oxidative tandem synthesis of dihydroquinazolines and quinolines from N-alkylanilines using a TEMPO oxoammonium salt as a mild and nontoxic oxidant has been developed. Fe(OTf)2 was the Lewis acid catalyst of choice for the formation of dihydroquinazolines, whereas FeCl3 led to better results for the synthesis of quinolines. This divergent approach implies that, for both syntheses, direct oxidative functionalization of a α-C(sp(3))-H bond of the N-alkylanilines occurs, leading to C-N bond formation or C-C bond formation upon homocondensation or reaction with simple olefins, respectively. Cyclization followed by a final oxidation generates these classes of interesting bioactive heterocycles in one synthetic transformation. Additionally, the one-pot multicomponent synthesis of quinolines from anilines, aldehydes, and olefins has also been successfully developed under these mild oxidative conditions.

Mild Metal‐Free Tandem α‐Alkylation/Cyclization ofN‐Benzyl Carbamates with Simple Olefins

Easy does it! The chemoselective oxidative α-C(sp(3))-H alkylation/cyclization reaction of N-benzyl carbamates using simple mono-, di-, and trisubstituted olefins provides functionalized N-heterocycles such as oxazinones. A TEMPO oxoammonium salt serves as the oxidant, making it possible to carry out the reaction at low temperatures. Neither a metal catalyst nor preactivation in the α-position to the nitrogen group are needed.

ChemInform Abstract: TEMPO Oxoammonium Salt Mediated Dehydrogenative Povarov/Oxidation Tandem Reaction of N‐Alkyl Anilines.

AbstractMono‐ and disubstituted olefins are suitable substrates in the process.

TEMPO Oxoammonium Salt-Mediated Dehydrogenative Povarov/Oxidation Tandem Reaction of N-Alkyl Anilines

The synthesis of a variety of substituted quinolines from N-alkyl anilines by a one-pot dehydrogenative Povarov/oxidation tandem reaction with mono- and 1,2-disubstituted aryl and alkyl olefins was developed. A simple protocol using cheap and benign iron(III)chloride as the Lewis acid catalyst and a TEMPO oxoammonium salt as a nontoxic, mild, efficient oxidant is reported.