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.

A redox-economical synthesis of trifluoromethylated enamides with the Langlois reagent.

A redox-economical strategy for the synthesis of trifluoromethylated enamides using copper catalysis is reported. The reaction employs the inexpensive Langlois reagent (CF3SO2Na) and takes place without the need of an external oxidant. The trifluoromethylated enamide products can easily be converted into the corresponding ketone, saturated amide or oxazole.

Diastereoselective Synthesis of Cyclopenta[c]furans by a Catalytic Multicomponent Reaction.

A diastereoselective three-component reaction between alkynyl enones, aldehydes and secondary amines is reported. With the aid of a benign indium catalyst, a range of highly substituted cyclopenta[c]furan derivatives can be obtained in a single-step procedure. The formation of the stereodefined heterocyclic motifs takes place via in situ generation of enamines followed by two sequential cyclization steps.

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.

Rhodium(II)-catalyzed asymmetric sulfur(VI) reduction of diazo sulfonylamidines.

Diazo sulfonylamidines readily undergo enantioselective oxygen transfer from sulfur to carbon atom in the presence of chiral rhodium(II) carboxylates resulting in chiral sulfinylamidines. This unusual asymmetric atom transfer "reduction" occurs rapidly under mild conditions, and sulfinylamidines are obtained in excellent yield.

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.

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 of Fluorinated Amide Derivatives via a Radical N-Perfluoroalkylation-Defluorination Pathway.

A one-pot approach to fluorinated hydroxamic acid, amide, and thioamide derivatives is reported. The reaction proceeds via an N-perfluoroalkylation of nitrosoarenes with perfluoroalkanesulfinates, resulting in labile N-perfluoroalkylated hydroxylamines. By the addition of suitable additives, a controllable oxy/thiodefluorination of the fluorinated hydroxylamine intermediates was achieved. The method highlights N-perfluoroalkylated amines as versatile intermediates for further synthesis.

Performance of SCS palladium pincer complexes in borylation of allylic alcohols. Control of the regioselectivity in the one-pot borylation-allylation process.

One-pot borylation-allylation reactions of aldehydes and allylic alcohols were performed under various reaction conditions. The borylation of allylic alcohols was performed using a very efficient SCS palladium pincer-complex catalyst. The regioselectivity of the allylation depends on the applied solvent. The reaction in CHCl3 gave the linear allylic product; however, when MeOH was added to the reaction mixture, the branched allylic product was formed.

Single-pot triple catalytic transformations based on coupling of in situ generated allyl boronates with in situ hydrolyzed acetals.

In situ hydrolyzed acetals were coupled with in situ generated allyl boronates in a one-pot procedure, affording regio- and stereodefined homoallyl alcohols, epoxides and amino alcohols.

Diastereoselective Synthesis of Polycyclic Indolizines with 2-(2-Enynyl)pyridines and Enamines.

A diastereoselective metal-catalyzed reaction of 2-(2-enynyl)pyridines and cyclic enamines is reported. The method provides access to a variety of substituted indolizine derivatives by variation of the enyne component and the reaction conditions. Performing the reaction using a preformed enamine led to the formation of polycyclic indolizines. With in situ generated enamines, ketone-containing indolizine derivatives were obtained. An asymmetric reaction of 2-(2-enynyl)pyridines and enamines generated from an aldehyde and a catalytic amount of amine is presented.

Stereoselective synthesis of bicyclo[3.n.1]alkenone frameworks by Lewis acid-catalysis.

An intermolecular cyclization of alkynyl enones with cyclic ketones for the synthesis of bicyclo[3.n.1]alkenones is reported. This protocol exhibits a high functional group tolerance and provides access to a variety of bicyclic systems found as skeletons in many natural products.

N-Trifluoromethylation of Nitrosoarenes with Sodium Triflinate.

A highly efficient N-trifluoromethylation of nitrosoarenes is reported. The inexpensive and convenient Langlois reagent (sodium triflinate) is employed as a CF3-radical source in combination with a copper catalyst and an oxidant. N-Trifluoromethylated hydroxylamines are obtained in high yields within 1 h at room temperature. The addition of hydroquinone was found to be instrumental to prevent the formation of side products. The method is high-yielding, is scalable, and displays a high functional group tolerance.

Para-Selective Halogenation of Nitrosoarenes with Copper(II) Halides.

The para-selective direct bromination and chlorination of nitrosoarenes with copper(II) bromide and chloride is reported. Under mild reaction conditions, a range of halogenated arylnitroso compounds are obtained in moderate to good yields with high regioselectivity. Additionally, the versatility of the method is demonstrated by the development of a one-pot procedure to obtain the corresponding para-halogenated aniline- and nitrobenzene derivatives.

Lewis Acid Catalyzed Annulation of Nitrones with Oxiranes, Aziridines, and Thiiranes.

A highly selective Lewis acid catalyzed annulation of three-membered heterocycles with nitrones has been developed. Oxiranes, aziridines, and thiiranes were used as substrates for the synthesis of various six-membered heterocycles using Al or In catalysts. This catalytic protocol demonstrates a broad substrate scope and provides access to new structural motifs in high yields and in excellent selectivity under mild reaction conditions.

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.