Nicklas Selander

Catalytic amide formation from non-activated carboxylic acids and amines

The amide functionality is found in a wide variety of biological and synthetic structures such as proteins, polymers, pesticides and pharmaceuticals. Due to the fact that synthetic amides are still mainly produced by the aid of coupling reagents with poor atom-economy, the direct catalytic formation of amides from carboxylic acids and amines has become a field of emerging importance. A general, efficient and selective catalytic method for this transformation would meet well with the increasing demands for green chemistry procedures. This review covers catalytic and synthetically relevant methods for direct condensation of carboxylic acids and amines. A comprehensive overview of homogeneous and heterogeneous catalytic methods is presented, covering biocatalysts, Lewis acid catalysts based on boron and metals as well an assortment of other types of catalysts.

Stereoselective 1,3-Insertions of Rhodium(II) Azavinyl Carbenes

Rhodium(II) azavinyl carbenes, conveniently generated from 1-sulfonyl-1,2,3-triazoles, undergo a facile, mild, and convergent formal 1,3-insertion into N-H and O-H bonds of primary and secondary amides, various alcohols, and carboxylic acids to afford a wide range of vicinally bisfunctionalized (Z)-olefins with perfect regio- and stereoselectivity. Utilizing the distinctive functionality installed through these reactions, a number of subsequent rearrangements and cyclizations expand the repertoire of valuable organic building blocks constructed by reactions of transition-metal carbene complexes, including α-allenyl ketones and amino-substituted heterocycles.

Arylation of rhodium(II) azavinyl carbenes with boronic acids.

A highly efficient and stereoselective arylation of in situ-generated azavinyl carbenes affording 2,2-diaryl enamines at ambient temperatures has been developed. These transition-metal carbenes are directly produced from readily available and stable 1-sulfonyl-1,2,3-triazoles in the presence of a rhodium carboxylate catalyst. In several cases, the enamines generated in this reaction can be cyclized into substituted indoles employing copper catalysis.

Ring Expansion and Rearrangements of Rhodium(II) Azavinyl Carbenes

Room for expansion: an efficient, regioselective, and convergent method for the ring expansion and rearrangement of 1-sulfonyl-1,2,3-triazoles under rhodium(II)-catalyzed conditions is described. These denitrogenative reactions form substituted enaminone and olefin-based products. The enaminone products can be further functionalized to give various heterocycles and ketone derivatives, thus rendering the sulfonyl triazole traceless.

Catalytic Allylic C−H Acetoxylation and Benzoyloxylation via Suggested (η3-Allyl)palladium(IV) Intermediates

Palladium-catalyzed allylic acetoxylations and benzoyloxylations were carried out using iodonium salts. The reactions proceed under mild conditions with high regio- and stereoselectivity. The catalysis can be performed under both acidic and nonacidic conditions without use of BQ or other external oxidants and activator ligands. Deuterium labeling experiments clearly show that the catalytic reaction proceeds through (eta(3)-allyl)palladium intermediates. A stoichiometric study with one of the catalysts provided evidence for the formation of a Pd(IV) species.

Selective C-H borylation of alkenes by palladium pincer complex catalyzed oxidative functionalization.

Selective C-H Borylation of Alkenes by Palladium Pincer Complex Catalyzed Oxidative Functionalization

Pincer complex-catalyzed redox coupling of alkenes with iodonium salts via presumed palladium(IV) intermediates

Palladium pincer complexes directly catalyze the redox coupling reactions of functionalized alkenes and iodonium salts. The catalytic process, which is suitable for mild catalytic functionalization of allylic acetates and electron-rich alkenes, probably occurs through Pd(IV) intermediates. Due to the strong metal-ligand interactions, the oxidation of phosphine and amine ligands of the pincer complexes can be avoided in the presented reactions.

Palladium-Catalyzed Allylic C−OH Functionalization for Efficient Synthesis of Functionalized Allylsilanes

A new method is described for palladium-catalyzed allylic silylation using allylic alcohols and disilanes as precursors. The reactions proceed smoothly under mild and neutral conditions, and this method is suitable for synthesis of regio- and stereodefined allylsilanes. The presented silylation reaction can be easily extended to include synthesis of allylboronates by change of the dimetallic reagent. The presented synthetic procedure offers a broad platform for the selective synthesis of functionalized allyl metal reagents, which are useful precursors in advanced organic chemistry and natural product synthesis.

Synthesis and transformation of organoboronates and stannanes by pincer-complex catalysts

Palladium pincer-complexes readily catalyze the formation of allylstannanes, allenylstannanes/silanes and allylboronates from easily available allylic and propargylic substrates and dimetallic reagents. The catalytic activity and selectivity of the pincer-complexes can efficiently be fine-tuned by changing the heteroatoms in the side arms. Pincer-complexes with nitrogen, sulfur and selenium atoms in the side arms are very efficient for creating C-Sn, C-Si and C-B bonds, while phosphorus based complexes can be employed for catalytic cleavage of C-Sn and C-B bonds. Most of the catalytic metallation (stannylation and borylation) processes can easily be combined with other reactions, and thus one-pot procedures can be designed for the synthesis of homoallylic alcohols, homoallylic amines and alpha-amino acids from simple precursors.

Divergent Iron-Catalyzed Coupling of O-Acyloximes with Silyl Enol Ethers

An iron-catalyzed coupling reaction of O-acyloximes and O-benzoyl amidoximes with silyl enol ethers is reported. The protocol provides access to functionalized pyrroles, 1,6-ketonitriles, pyrrolines and imidazolines via carbon-centered radicals generated from an initially formed iminyl radical. The intramolecular cyclization and ring-opening processes of the iminyl radical take place preferentially over reactions that proceed through a 1,3-hydrogen transfer, providing insights into iron-catalyzed reactions with oxime derivatives. The cheap and environmentally friendly iron catalyst, the broad substrate scope and the functional group compatibility make this protocol useful for synthesis of valuable nitrogen-containing products.