Cobalt-Catalyzed Aerobic Oxidative Dearomatization of 2-Aryl Indoles and in situ [3+2] Annulation with Enamides

Chemistry of 3-cyanoacetyl indoles: synthesis, reactions and applications: a recent update

Indole is a significant nitrogen-based heterocycle with particular importance in the synthesis of heterocyclic scaffolds. Indole based compounds have been recently attracting much attention due to their biological and pharmaceutical activities. 3-Substituted indoles such as cyanoacetyl indoles (CAIs) are nitrogen-heterocyclic compounds which are easily obtained from the reaction of indoles and cyanoacetic acid. They are versatile starting materials utilized for the construction of a wide variety of molecules containing indole moieties in organic synthesis. In this study, we provide an overview on the synthesis of 3-cyanoacetyl indoles (CAIs) and their recent applications in the multi-component reactions for the synthesis of various heterocyclic compounds such as pyranes, pyridines, dihydropyridines, pyrimidines, tetrahydropyrimidines, pyrazoles, pyrazolopyridines, pyrazolopyrimidines, pyridopyrimidines, tetrazolopyrimidines, triazolopyrimidines, furans, dihydrofurans, coumarins, pyrimido naphthyridines, chromenes, thiazoles, pyrimidoindazoles, pyrazoloquinolines, isoxazolopyridines, and carbazoles and their biological activities during the period of 2013 to 2022.

Diastereoselective Access to Triazolo[1,2-a]indolines via a Bio-Inspired Oxidative Cyclization of NH-Indoles

Establishing three-dimensional chemicals by using the C₂-C₃ π bond of indoles has always been a research hotspot in organic synthesis; however, employing the oxidative C₂-C₃ π bond of indoles to generate imine which would lead to the N₁-C₂ π bond cyclization under metal-free conditions is still rare. Here, we report a bio-inspired synthesis of triazolo[1,2-a]indolines by the oxidative cyclization between NH-indoles and azomethine imines with 3,3-dimethyldioxirane as the sole oxidant under metal-free and mild conditions. This finding represents an elegant instance of tri-functionalization of NH-indoles, which provides rapid access to a broad range of triazolo[1,2-a]indolines with tetrahydroisoquinolines in one single step. Up to 86% yield and above 20:1 dr value are observed. The radical mechanism and proton migration process have been speculated.

Dearomatization of 3-Nitroindoles Enabled Using Palladium-Catalyzed Decarboxylative [4 + 2] Cycloaddition of 2-Alkylidenetrimethylene Carbonates

A dearomatization process of 3-nitroindoles enabled using palladium-catalyzed decarboxylative [4 + 2] cycloaddition of either 2-alkylidenetrimethylene carbonates or 2-(hydroxymethyl)-3-arylallyl carbonates has been developed, affording a wide range of indoline-fused tetrahydropyrans in good yields with excellent diastereoselectivities. This reaction features a wide substrate scope and mild conditions and represents the first example of the application of π-allyl palladium 1,4-[O,C]-dipole species for the dearomative cycloaddition of electron-deficient heteroarenes.