Synthesis of chiral systems featuring the pyrrole unit: a review

Synthetic strategies towards pyrroles within chiral frameworks are summarised, focussing on reports published 2010-2023. The synthesis of pyrroles featuring substituents bearing chiral centres are summarised, as are those whereby pyrroles are located within axially chiral systems courtesy of restricted bond rotation.

Nitro and Other Electron Withdrawing Group Activated Ruthenium Catalysts for Olefin Metathesis Reactions

Advanced applications of the Nobel Prize winning olefin metathesis reaction require user-friendly and highly universal catalysts. From many successful metathesis catalysts, which belong to the two distinct classes of Schrock and Grubbs-type catalysts, the subclass of chelating-benzylidene ruthenium complexes (so-called Hoveyda-Grubbs catalysts) additionally activated by electron-withdrawing groups (EWGs) provides a highly tunable platform. In the Review, the origin of the EWG-activation concept and selected applications of the resulting catalysts in target-oriented synthesis, medicinal chemistry, as well as in the preparation of fine-chemicals and in materials chemistry is discussed. Based on the examples, some suggestions for end-users regarding minimization of catalyst loading, selectivity control, and general optimization of the olefin metathesis reaction are provided.

Enantioselective Synthesis of Pyrrolizidinone Scaffolds through Multiple-Relay Catalysis

A triple-tandem protocol for the synthesis of the pyrrolizidinone skeleton has been devised. It involves a cross metathesis-intramolecular aza-Michael reaction-intramolecular Michael addition tandem sequence, starting from N-pentenyl-4-oxo-2-alkenamides and conjugated ketones. In the presence of two cooperative catalysts, namely the second-generation Hoveyda-Grubbs catalyst and (R)-TRIP-derived BINOL phosphoric acid, this multiple-relay catalytic process takes place in good yields and outstanding levels of diastero- and enantioselectivity with the simultaneous generation of three contiguous stereocenters.

Tandem Organocatalytic Cycloaromatization/Intramolecular Friedel-Crafts Alkylation Sequence for the Synthesis of Indolizinones and Pyrrolo-azepinone Derivatives

The organocatalytic synthesis of indolizinones and pyrrolo-azepinones has been accomplished in a tandem fashion through a sequence that comprises initial cycloaromatization followed by intramolecular Friedel-Crafts alkylation. The process takes place under Brønsted acid catalysis, giving rise to final products in moderate to good yields. Attempts to carry out the tandem protocol in an enantioselective fashion were performed with chiral (R)-BINOL-derived N-triflyl phosphoramides. After initial optimization, the tandem process took place with moderate levels of enantioselectivity.

Brønsted Acid-Catalyzed Formal [2 + 2 + 1] Annulation for the Modular Synthesis of Tetrahydroindoles and Tetrahydrocyclopenta[ b]pyrroles

An expedient synthesis of tetrahydroindoles and tetrahydrocyclopenta[ b]pyrroles, highlighted by Brønsted acid catalyzed formal [2 + 2 + 1] annulation reaction, is reported. Using three readily accessible reaction components, i.e., an electrophilic species in silyloxyallyl cations and two distinct nucleophiles in silylenol ethers and amines, our chemistry enables the assembly and functionalization of these biologically important N-heterocycles in a highly modular manner.

Methods for the synthesis of annulated pyrroles via cyclisation strategies

In this report, we review the methods that have been employed to synthesise annulated pyrroles.

Enantioselective palladium-catalyzed C–H functionalization of pyrroles using an axially chiral 2,2′-bipyridine ligand

An enantioselective palladium-catalyzed C–H functionalization of pyrroles with diazoacetates has been developed with up to 90% of enantioselectivity.

Catalytic Asymmetric Conjugate Addition of Indolizines to α,β-Unsaturated Ketones

A catalytic enantioselective conjugate addition of indolizines to enones is described. The chiral phosphoric acid (S)-TRIP activates α,β-unsaturated ketones, thereby promoting an enantioface-differentiating attack by indolizines. Using this reaction, several alkylated indolizines were synthesized in good yields and with enantiomeric ratios of up to 98:2.