Benzo[b]Furan in the Povarov Reaction

Diastereoselective multicomponent synthesis of dihydroisoindolo[2,1-a]quinolin-11-ones mediated by eutectic solvents

In this contribution, a series of dihydroisoindolo[2,1-a]quinolin-11-ones was synthesized by a one-pot multicomponent Povarov reaction starting from anilines, alkenes (trans-anethole, methyl eugenol and indene) and 2-formylbenzoic acid. Different eutectic solvents bearing Lewis or Brønsted acids were evaluated as reaction media and catalysts for the model reaction employing p-toluidine and trans-anethole finding that the eutectic mixture ChCl/ZnCl2 (1/2) allowed the obtention of the target compound in 77% isolated yield. Under the optimized reaction conditions, 20 derivatives were obtained in good to moderated yields using meta- and para-susbstituted anilines, while the corresponding ortho-analogs followed a different pathway affording isoindolinones. In addition, the eutectic mixture was reused in six cycles without observing a detrimental catalytic activity. This methodology features mild reaction conditions, short reaction time, simple work-up, and utilization of a reusable solvent; and provides straightforward and diastereoselective access to these alkaloid-like heterocyclic molecules.

The Povarov Reaction: A Versatile Method to Synthesize Tetrahydroquinolines, Quinolines and Julolidines

The multicomponent Povarov reaction represents a powerful approach for the construction of substances containing N-heterocyclic frameworks. By using the Povarov reaction, in addition to accessing tetrahydroquinolines, quinolines and julolidines in a single step, it is possible to form the following new bonds: two Csp 3–Csp 3 and one Csp 3–Nsp 3, two Csp 2–Csp 2 and one Csp 2–Nsp 2, and four Csp 3–Csp 3 and two Csp 3–Nsp 1, respectively. This short review discusses the main features of the Povarov reaction, including its mechanism, the reaction scope by employing different catalysts and substrates, as well as stereoselective versions.

1 Introduction

2 Mechanism of the Povarov Reaction

3 Tetrahydroquinolines

4 Quinolines

5 Julolidines

6 Concluding Remarks

Organocatalytic Asymmetric Three-Component Povarov Reactions of Anilines and Aldehydes

We report the first highly enantio- and diastereoselective three-component Povarov reaction between anilines and aldehydes catalyzed by a chiral amine catalyst. A wide variety of substituted tetrahydroquinolines were obtained with moderate to good yields and excellent enantioselectivity and diastereoselectivity (up to 99% ee and >95:5 dr) under the reaction conditions. Furthermore, the reaction intermediates could be efficiently converted to other valuable building blocks.

Synthesis of Nitrogen-Containing Polyaromatics by Aza-Annulative π-Extension of Unfunctionalized Aromatics

Nitrogen-containing polycyclic aromatic compounds (N-PACs) are an important class of compounds in materials science. Reported here is a new aza-annulative π-extension (aza-APEX) reaction that allows rapid access to a range of N-PACs in 11-84 % yields from readily available unfunctionalized aromatics and imidoyl chlorides. In the presence of silver hexafluorophosphate, arenes and imidoyl chlorides couple in a regioselective fashion. The follow-up oxidative treatment with p-chloranil affords structurally diverse N-PACs, which are very difficult to synthesize. DFT calculations reveal that the aza-APEX reaction proceeds through the formal [4+2] cycloaddition of an arene and an in situ generated diarylnitrilium salt, with sequential aromatizations having relatively low activation energies. Transformation of N-PACs into nitrogen-doped nanographenes and their photophysical properties are also described.

Visible-Light-Mediated Aerobic Tandem Dehydrogenative Povarov/Aromatization Reaction: Synthesis of Isocryptolepines

A metal‐free, photoinduced aerobic tandem amine dehydrogenation/Povarov cyclization/aromatization reaction between N‐aryl glycine esters and indoles leads to tetracyclic 11H‐indolo[3,2‐c]quinolines under mild conditions and with high yields. The reaction can be performed by using molecular iodine along with visible light, or by combining an organic photoredox catalyst with a halide anion. Mechanistic studies reveal that product formation occurs through a combination of radical‐mediated oxidation steps with an iminium ion or N‐haloiminium ion [4+2]‐cycloaddition, and the N‐heterocyclic products constitute new analogues of the antiplasmodial natural alkaloid isocryptolepine.

Progress in the Chemistry of Tetrahydroquinolines

Tetrahydroquinoline is one of the most important simple nitrogen heterocycles, being widespread in nature and present in a broad variety of pharmacologically active compounds. This Review summarizes the progress achieved in the chemistry of tetrahydroquinolines, with emphasis on their synthesis, during the period from mid-2010 to early 2018.

Oxidation of active sp3C–H bonds initiated consecutive intermolecular/intramolecular cyclization between glycine derivatives ando-vinylphenols: construction of a polycyclic benzofuroquinoline skeleton

The construction of the polycyclic benzofuroquinoline skeleton was realized through a consecutive cyclization.