Highly Enantioselective Ferrocenyl Palladacycle-Acetate Catalysed Arylation of Aldimines and Ketimines with Arylboroxines

Metastable Charged Dimers in Organometallic Species: A Look into Hydrogen Bonding between Metallocene Derivatives

Multiply charged complexes bound by noncovalent interactions have been previously described in the literature, although they were mostly focused on organic and main group inorganic systems. In this work, we show that similar complexes can also be found for organometallic systems containing transition metals and deepen in the reasons behind the existence of these species. We have studied the structures, binding energies, and dissociation profiles in the gas phase of a series of charged hydrogen-bonded dimers of metallocene (Ru, Co, Rh, and Mn) derivatives isoelectronic with the ferrocene dimer. Our results indicate that the carboxylic acid-containing dimers are more strongly bonded and present larger barriers to dissociation than the amide ones and that the cationic complexes tend to be more stable than the anionic ones. Additionally, we describe for the first time the symmetric proton transfer that can occur while in the metastable phase. Finally, we use a density-based energy decomposition analysis to shine light on the nature of the interaction between the dimers.

Nickel-Catalyzed Enantioselective Reductive Arylation and Heteroarylation of Aldimines via an Elementary 1,4-Addition

Nickel catalysts of chiral pyrox ligands promoted enantioselective reductive arylation and heteroarylation of aldimines, using directly (hetero)aryl halides and sulfonates. The catalytic arylation can also be conducted with crude aldimines generated from condensation of aldehydes and azaaryl amines. Mechanistically, density functional theory (DFT) calculations and experiments pointed to an elementary step of 1,4-addition of aryl nickel(I) complexes to N-azaaryl aldimines.

Catalytic Asymmetric Synthesis of Tröger's Base Analogues with Nitrogen Stereocenter

Nitrogen stereocenters are common chiral units in natural products, pharmaceuticals, and chiral catalysts. However, their research has lagged largely behind, compared with carbon stereocenters and other heteroatom stereocenters. Herein, we report an efficient method for the catalytic asymmetric synthesis of Tröger's base analogues with nitrogen stereocenters via palladium catalysis and home-developed GF-Phos. It allows rapid construction of a new rigid cleft-like structure with both a C- and a N-stereogenic center in high efficiency and selectivity. A variety of applications as a chiral organocatalyst and metallic catalyst precursors were demonstrated. Furthermore, DFT calculations suggest that the NH···O hydrogen bonding and weak interaction between the substrate and ligand are crucial for the excellent enantioselectivity control.

Direct Enantioselective Addition of Alkynes to Imines by a Highly Efficient Palladacycle Catalyst

Enantiopure propargylic amines are highly valuable synthetic building blocks. Much effort has been devoted to develop methods for their preparation. The arguably most important strategy is the 1,2-addition of alkynes to imines. Despite remarkable progress, the known methods using Zn and Cu catalysts suffer from the need for high catalyst loadings, typically ranging from 2-60 mol % for neutral aldimine substrates. Here we report a planar chiral Pd complex acting as very efficient catalyst for direct asymmetric alkyne additions to imines, requiring very low catalyst loadings. Turnover numbers of up to 8700 were accomplished. Our investigation suggests that a Pd-acetylide complex is generated as a catalytically relevant intermediate by the aid of an acac ligand acting as internal catalytic base. It is shown that the catalyst is quite stable under the reaction conditions and that product inhibition is not an issue. A total of 39 examples is shown which all yielded almost enantiopure products.

Enantioselective construction of a congested quaternary stereogenic center in isoindolinones bearing three aryl groups via an organocatalytic formal Betti reaction

An efficient enantioselective formal Betti reaction between phenols and diaryl ketimines generated in situ from isoindolinone alcohols is described.

Nickel(II)-Catalyzed Addition of Aryl and Heteroaryl Boroxines to the Sulfinylamine Reagent TrNSO: The Catalytic Synthesis of Sulfinamides, Sulfonimidamides, and Primary Sulfonamides

We report a redox-neutral Ni(II)-catalyzed addition of (hetero)aryl boroxines to N-sulfinyltritylamine (TrNSO). The reactions use a catalyst generated from the combination of commercial, air-stable NiCl₂·(glyme) and a commercially available bipyridine ligand, and deliver sulfinamide products. The scope of the reaction is established using a sulfonimidamide synthesis, in which the initially formed sulfinamides undergo oxidative chlorination with the inexpensive and safe chlorinating agent, trichloroisocyanuric acid (TCCA), to produce sulfonimidoyl chlorides as key intermediates. These are combined in situ with a range of amines to deliver sulfonimidamides. The sulfonimidoyl chlorides can also be elaborated into primary sulfonamides via hydrolysis, and sulfonimidoyl fluorides via treatment with fluoride. These transformations are all achieved using one-pot procedures. Unprotected, primary sulfinamides are also available. For larger-scale reactions, the catalyst loading can be reduced to 1 mol %.

Enantioselective C,P-Palladacycle-Catalyzed Arylation of Imines

Chiral diarylmethylamines are of great interest because of their prevalence in biological and pharmaceutical sciences. Herein, we report a C,P-palladacycle-catalyzed enantioselective synthesis of chiral diarylmethylamines via asymmetric arylation of N-protected imines with arylboronic acids. The C,P-palladacycle showed high reactivity (up to 99% yield) and enantioselectivity (up to 99% ee) toward this arylation, enabling the tolerance of a wide range of functionalities, providing a convenient and efficient access to enantiomerically enriched diarylmethylamines. The absolute configuration of the product was well rationalized by the proposed stereochemical pathway and the catalytical cycle.

Stereospecific Asymmetric Synthesis of Tertiary Allylic Alcohol Derivatives by Catalytic [2,3]-Meisenheimer Rearrangements

Chiral acyclic tertiary allylic alcohols are very important synthetic building blocks, but their enantioselective synthesis is often challenging. A major limitation in catalytic asymmetric 1,2-addition approaches to ketones is the enantioface differentiation by steric distinction of both ketone residues. Herein we report the development of a catalytic asymmetric Meisenheimer rearrangement to overcome this problem, as it proceeds in a stereospecific manner. This allows for high enantioselectivity also for the formation of products in which the residues at the generated tetrasubstituted stereocenter display a similar steric demand. Low catalyst loadings were found to be sufficient and the reaction conditions were mild enough to tolerate even highly reactive functional groups, such as an enolizable aldehyde, a primary tosylate, or an epoxide. Our investigations suggest an intramolecular rearrangement pathway.

Electronic and Steric Tuning of an Atropisomeric Disulfoxide Ligand Motif and Its Use in the Rh(I)-Catalyzed Addition Reactions of Boronic Acids to a Wide Range of Acceptors

A novel chiral disulfoxide ligand pair bearing fluorine atoms at the 6 and 6' position of its atropisomeric backbone, ( M, S, S)- and ( P, S, S)- p-Tol-6F-BIPHESO, was synthesized. Complexation to a rhodium(I) precursor gave rise to μ-Cl- and μ-OH-bridged rhodium dimer complexes incorporating the new ( M, S, S)- p-Tol-6F-BIPHESO ligand, while its sibling ( P, S, S)- p-Tol-6F-BIPHESO was not complexed efficiently to the rhodium precursor. The performance of this disulfoxide ligand [( M, S, S)- p-Tol-6F-BIPHESO] in catalysis was tested in both 1,4- and 1,2-addition reactions of arylboronic acids. We show that addition to both cyclic and acyclic enones as well as N-tosylarylimines proceeds with high yields and high enantioselectivities to give the corresponding products. The synthesis of enantiomerically pure p-Tol-6F-BIPHESO is straightforward and inexpensive which, together with the high catalytic performance and wide substrate scope for these addition reactions, makes it a very attractive alternative to more classical chiral ligand entities.