Rhodium complex-catalyzed reaction of isonitriles with carbonyl compounds: catalytic synthesis of pyrroles

Improved Synthesis of Functionalized 2,2‘-Bipyrroles

A series of 2,2'-bipyrroles has been efficiently synthesized using an improved synthetic approach based on Pd(0)-catalyzed homocoupling of various 2-iodopyrroles. This new synthetic approach takes place at room temperature and in the presence of water. Functional groups such as formyl, ester, and nitrile are able to survive these reaction conditions. Solvents are found to play an important role in this reaction.

Recent Progress in the Catalytic Synthesis of Imidazoles

Imidazole is one of the important heteroaromatic compounds that have found a broad range of uses in, for example, pharmaceutical and industrial applications. Several conventional methodologies for the synthesis of imidazole rings are known; however, they are limited in terms of substrate generality and are not always efficient. Recent studies toward the development of catalytic reactions have brought significant improvements to the preparation of imidazoles. This Focus Review highlights the very recent progress in the catalytic synthesis of imidazoles, particularly those involving the formation of five-membered ring cores.

1,2-Sulfanyl Group Migration as a Driving Force: New Approach to Pyrroles by Reaction of Allenic Aldehydes with Amines

[reaction: see text] Acid-promoted reaction of sulfanyl group substituted allenic aldehyde with amine affords pyrrole derivatives in high yields. The neighboring group participation of the sulfanyl group is the driving force in this transformation.

An Efficient Highly Regioselective Synthesis of 2,3,4-Trisubstituted Pyrroles by Cycloaddition of Polarized Ketene S,S- and N,S-Acetals with Activated Methylene Isocyanides

An efficient route for regioselective synthesis of 2,3,4- substituted pyrroles allowing precise control over the introduction of a number of substituents and functionalities (tosyl, carbalkoxy, aryl, cyano, nitro, acetyl, benzoyl, cyclic amines, etc.) at the three positions of the pyrrole ring has been developed via 1,3-dipolar cycloaddition of readily accessible polarized ketene S,S- and N,S-acetals with carbanions derived from activated methylene isocyanides.

Thiazolium-Catalyzed Additions of Acylsilanes: A General Strategy for Acyl Anion Addition Reactions

A strategy utilizing N-heterocyclic carbenes (NHCs) derived from thiazolium salts has been developed for the generation of carbonyl anions from acylsilanes. Synthetically useful 1,4-diketones and N-phosphinoyl-alpha-aminoketones have been prepared in good to excellent yields via NHC-catalyzed additions of acylsilanes to the corresponding alpha,beta-unsaturated systems and N-phosphinoylimines. These organocatalytic reactions are air- and water-tolerant methods to execute robust carbonyl anion addition reactions. Additionally, polysubstituted aromatic furans and pyrroles have been efficiently synthesized in a one-pot process using this carbonyl anion methodology. The addition of alcohols to the reaction renders the process catalytic in thiazolium salt. In an effort to synthesize a potential intermediate along the proposed reaction pathway, silylated thiazolium carbinols have been identified to provide good yields of carbonyl anion addition products when subjected to the standard reaction conditions in the presence of suitable electrophiles.

Three-Step Solution-Phase Combinatorial Access to 1,2-Disubstituted and 1,2,5-Trisubstituted Pyrroles from Carboxylic Esters

An efficient diversity-oriented strategy has been developed for the solution-phase parallel synthesis of di- and trisubstituted pyrrole libraries. Methyl esters 1 were effectively converted to 1,2-di- and 1,2,5-trisubstituted pyrroles 5 and 6 in three steps. Treatment of ester 1 with vinylmagnesium bromide in the presence of copper (I) cyanide yielded the corresponding homoallylic ketone 2, which was subjected to ozonolysis or Tsuji-Wacker oxidation to yield the respective cyclization precursors 3 and 4 after aqueous workup. Compounds 3 and 4 were condensed without further purification with a primary amine to afford the desired 1,2-di- or 1,2,5-trisubstituted pyrroles 5 and 6 in good yield and purity.

Catalytic Multicomponent Synthesis of Highly Substituted Pyrroles Utilizing a One-Pot Sila-Stetter/Paal−Knorr Strategy

[reaction: see text] A multicomponent synthesis of highly substituted pyrroles catalyzed by thiazolium salts has been disclosed. The reaction employs an acyl anion conjugate addition reaction of acylsilanes (sila-Stetter) and unsaturated ketones to generate 1,4-dicarbonyl compounds in situ. The subsequent addition of various amines promotes a Paal-Knorr reaction, affording the desired pyrrole nucleus in an efficient one-pot process.