Solvent‐Free Synthesis of Pyrroles: An Overview

Mild and Catalytic Synthesis of Pyrroles from Vinyl Ethynylethylene Carbonates

A tandem remote propargylic amination/ring closure/aromatization reaction of vinyl ethynylethylene carbonates and amines has been developed, successfully constructing pyrrole derivatives. The reaction features mild conditions, high regioselectivity, high yields, and good functional group tolerance, making it an efficient method for pyrrole synthesis. Importantly, a variety of substrates containing natural product skeletons could also be compatibly and efficiently converted into pyrroles under the reaction conditions.

Cp*Ir(III) complexes catalyzed solvent-free synthesis of quinolines, pyrroles and pyridines via an ADC strategy

A trio of Ir(III) complexes that are held together by a picolinamidato moiety were created. In our earlier research, we demonstrated the catalytic activity of the complexes for producing alpha-alkylated ketones from a ketone or secondary alcohol with a primary alcohol in the presence of a catalytic amount of a Cp*Ir(III) catalyst and tBuOK in toluene at 110 °C using the hydrogen-borrowing technique. Earlier many research groups had synthesized quinoline, pyrrole, and pyridine derivatives using 2-amino alcohol and ketone or secondary alcohol derivatives as starting materials, but in all those cases the reaction conditions are not suitable in terms of green synthesis like more catalyst loading, base loading, long reaction time, and high temperature. In addition, most of the reactions contain phosphine a hazardous by-product, along with the catalyst. Keeping in mind these shortcomings, we tried to expand the use of our catalysts after achieving an excellent result in our previous work, and we were successful in producing quinoline, pyrrole, and pyridine derivatives through acceptor-less dehydrogenative coupling (ADC) procedures at 90-110 °C under neat/solvent-free conditions and achieved good to exceptional yields of those nitrogen-containing heterocycles. This methodology is attractive because it is environmentally benign and allows for the "green" synthesis of nitrogen-containing heterocycles. All that is required is a modest quantity of catalyst and base, and the by-products are merely H2O and H2.

Functionalized 2,3'-Bipyrroles and Pyrrolo[1,2-c]imidazoles from Acylethynylpyrroles and Tosylmethylisocyanide

An efficient method for the synthesis of pharmaceutically prospective but still rare functionalized 2,3'-bipyrroles (in up to 80% yield) by the cycloaddition of easily available acylethynylpyrroles with tosylmethylisocyanide (TosMIC) has been developed. The reaction proceeds under reflux (1 h) in the KOH/THF system. In the t-BuONa/THF system, TosMIC acts in two directions: along with 2,3'-bipyrroles, the unexpected formation of pyrrolo[1,2-c]imidazoles is also observed (products ratio~1:1).

Copper/Nitroxyl-Catalyzed Synthesis of Pyrroles by Oxidative Coupling of Diols and Primary Amines at Room Temperature

The Cu/ABNO-catalyzed aerobic oxidative coupling of diols and primary amines to access N-substituted pyrroles is highlighted (ABNO = 9-azabicyclo[3.3.1]nonane N-oxyl). The reaction proceeds at room temperature with an O₂ balloon as the oxidant using commercially available materials as the substrates and catalysts. The catalyst system is characterized by a broad range of substrates and a good tolerance to sensitive functional groups. The gram-scale experiment proves this system's practicability.

Flexible Construction Approach to the Synthesis of 1,5-Substituted Pyrrole-3-carbaldehydes from 5-Bromo-1,2,3-triazine

We report an efficient and mild tandem catalytic process for the synthesis of functionalized pyrrole-3-carbaldehydes. These compounds were obtained by a one-pot three-component reaction of 5-bromo-1,2,3-triazine, terminal alkynes, and primary amines via a palladium-catalyzed Sonogashira coupling reaction, and then annulation through a silver-mediated reaction of the resulting alkynyl 1,2,3-triazines allowed for access to the multifunctionalized pyrrole-3-carbaldehydes.