Enantioselective synthesis of polycyclic pyrrole derivatives by iridium-catalyzed asymmetric allylic dearomatization and ring-expansive migration reactions

Catalytic Asymmetric De Novo Synthesis of Chiral Pyrroles Through Desymmetrizing Oxidative [3+2]-Cycloaddition and the Van Leusen Reaction

Central chirality in heteroarene derivatives arising from unsymmetrically substituted heteroarene rings is an intriguing but underexplored topic. Herein, we reported the first catalytic enantioselective de novo construction of centrally chiral pyrroles through desymmetrizing oxidative [3+2]-cycloaddition by employing silver catalysis. This judicious desymmetrization can produce at least four continuous stereogenic centers without creating any additional stereocenter. Furthermore, to introduce a more diverse set of substituents, we developed the first catalytic asymmetric Van Leusen reaction with α-substituted TosMIC for the synthesis of centrally chiral pyrroles. A wide range of polycyclic 2-substituted, 3,4-fused pyrroles were obtained in high yields and with good to high enantioselectivities. This report includes the elaboration of methanobenzo[f]isoindole to synthetically challenging building block chiral isoindole compounds, which are synthesized enantioselectively for the first time.

Application of Metal-Free Dearomatization Reaction as a Sustainable Strategy to Direct Access Complex Cyclic Compounds

The highly efficient construction of complicated heterocyclic frameworks in an atom- and step-economic manner is still one of the cores of synthetic chemistry. Dearomatization reactions show the unique advantage for the construction of functionalized heterocycles and have attracted widespread attention over the past two decades. The metal-free approach has proved to be a green and sustainable paradigm for the synthesis of spirocyclic, polycyclic and heterocyclic scaffolds, which are widely present in natural products and bioactive molecules. In this review, the advances in the recent six years (2017-2023) in metal-free dearomatization reactions are highlighted. Emphasis is placed on developments in the field of organo-catalyzed dearomatization reactions, oxidative dearomatization reactions, Brønsted acid- or base-promoted dearomatization reactions, photoredox-catalyzed dearomatization reactions, and electrochemical oxidation dearomatization reactions.

Copper-catalyzed three-component annulation toward pyrroles via the cleavage of two C-C bonds in 1,3-dicarbonyls

The first copper-catalyzed three-component annulation of α,β-unsaturated ketoximes, 1,3-dicarbonyls and paraformaldehyde has been documented. This novel strategy achieved the two C-C bond cleavage of 1,3-dicarbonyl compounds directly as a single-carbon synthon and provided a new and highly efficient method for the synthesis of 2,3-disubstituted pyrroles in moderate to good yields with broad functional group compatibility.

Palladium-Catalyzed Dearomatization of Indoles with Alkynes: Construction of Spirocyclohexaneindolenines

A palladium-catalyzed dearomatization of indoles with alkynes has been developed, providing an efficient route to access a variety of synthetically useful spirocyclohexaneindolenines in moderate to good yields. The current method features a simple catalytic system, operational simplicity, and good functional group compatibility, which will contribute substantially to the development of dearomatization to access spiro compounds. Besides, the ubiquitous existence of spiro molecules, including spirocyclohexaneindolenines, in drugs and biological active molecules suggests the potential application of this methodology in medicinal chemistry.

Enantioselective Synthesis of Functionalized Tetrahydropyridines through Iridium-Catalyzed Formal [5+1] Annulation

An efficient iridium-catalyzed asymmetric formal [5+1] annulation by in situ generation of enamines as N-nucleophiles for the synthesis of tetrahydropyridine derivatives is disclosed. The methodology offers direct access to a wide variety of chiral tetrahydropyridine derivatives in moderate to good yields and excellent enantioselectivity.