Application of a New Bicyclic Triaminophosphine Ligand in Pd-Catalyzed Buchwald−Hartwig Amination Reactions of Aryl Chlorides, Bromides, and Iodides

Electrogenerated Nickel Catalyst for C-N Cross-Coupling

Arylamines represent a class of compounds widely found in natural products and pharmaceuticals. Among methodologies devoted to their synthesis, nickel-catalyzed amination of aryl halides constitutes one of the most employed conventional strategies. However, C-N cross-couplings often involve elaborated nickel complexes, which are expensive and/or air and moisture sensitive. To circumvent this issue, we herein report an electrochemical method based on a sacrificial anode process to in situ generate a catalytic amount of nickel salts allowing amination of aryl halides. The approach, simple to set up, proceeds under mild reaction conditions and enables access to a large panel of arylamines.

Synthesis of 3-aryl-1-phosphinoimidazo[1,5-a]pyridine ligands for use in Suzuki-Miyaura cross-coupling reactions

3-Aryl-1-phosphinoimidazo[1,5-a]pyridine ligands were synthesized from 2-aminomethylpyridine as the initial substrate via two complementary routes. The first synthetic pathway underwent the coupling of 2-aminomethylpyridine with substituted benzoyl chlorides, followed by cyclization, iodination and palladium-catalyzed cross-coupling phosphination reactions sequence to give our phosphorus ligands. In the second route, 2-aminomethylpyridine was cyclized with aryl aldehydes, followed by the iodination and palladium-catalyzed cross-coupling phosphination reactions to yield our phosphorus ligands. The 3-aryl-1-phosphinoimidazo[1,5-a]pyridine ligands were evaluated in palladium-catalyzed sterically-hindered biaryl and heterobiaryl Suzuki-Miyaura cross-coupling reactions.

Encapsulation of Azaphosphatranes and Proazaphosphatranes in Confined Spaces

Proazaphosphatranes (also named Verkade's superbases) and their azaphosphatrane conjugated acids have been recently been shown to be confined in either covalent or self-assembled molecular cages, or immobilized in nanopores of hybrid materials. The encapsulation of these phosphorus moieties turns out to strongly affect both their acid-base, catalytic, and recognition properties. The thermodynamics and kinetics of the proton transfer as well as the selectivity and catalytic activities of Verkade's superbases were strongly changed upon their confinement in a hemicryptophane cavity. Moreover, self-assembled cages, including azaphosphatrane moieties, were found to display remarkable anion recognition properties in water. In this Minireview, these new aspects of the chemistry of aza- and proaza-phosphatranes are presented, in order to highlight the great potential of such an approach.

On Transannulation in Azaphosphatranes: Synthesis and Theoretical Analysis

A combined synthetic-theoretical study has been undertaken to determine the factors that influence transannulation in azaphosphatranes. The commonly used proazaphosphatrane P(i-BuNCH₂CH₂)₃N and several of its oxidized congeners are used as model systems. The haloazaphosphatranes of P(i-BuNCH₂CH₂)₃N were synthesized, including a rare fluoroazaphopshatrane, and used as references for computational investigations. Comparisons of the experimental and theoretical observations highlight the flexibility observed in transannulated atranes and the potential for multiple local energetic minima depending on the identity of the equatorial substituents for a given azaphosphatrane. Theoretical calculations also identify the role of the ethylene linker in azaphosphatrane bonding, the influence of transannulation on P-electrophile interactions, and the contribution of electrostatic interactions to transannulation.

New conjugated poly(pyridinium salt) derivative: AIE characteristics, the interaction with DNA and selective fluorescence enhancement induced by dsDNA

Fluorescence turn-on DNA sensor with excellent sensitivity and selectivity is developed based on a new conjugated poly(pyridinium salt) with AIE characteristics. The probe is also successfully utilized to follow the DNA cleavage process by DNase I.

Halogen-enriched fragment libraries as chemical probes for harnessing halogen bonding in fragment-based lead discovery

Halogen bonding has recently experienced a renaissance, gaining increased recognition as a useful molecular interaction in the life sciences. Halogen bonds are favorable, fairly directional interactions between an electropositive region on the halogen (the σ-hole) and a number of different nucleophilic interaction partners. Some aspects of halogen bonding are not yet understood well enough to take full advantage of its potential in drug discovery. We describe and present the concept of halogen-enriched fragment libraries. These libraries consist of unique chemical probes, facilitating the identification of favorable halogen bonds by sharing the advantages of classical fragment-based screening. Besides providing insights into the nature and applicability of halogen bonding, halogen-enriched fragment libraries provide smart starting points for hit-to-lead evolution.

Palladium-catalyzed synthesis of natural and unnatural 2-, 5-, and 7-oxygenated carbazole alkaloids from N-arylcyclohexane enaminones

A palladium-catalyzed synthesis of the carbazole framework is described, including the preparation of 2-, 5-, and 7-oxygenated natural and unnatural carbazole alkaloids. A series of N-arylcyclohexane enaminones, generated by condensation of cyclohexane-1,3-dione with diverse anilines, were aromatized by a Pd(0)-catalyzed thermal treatment to afford the corresponding diarylamines. The latter were submitted to a Pd(II)-catalyzed cyclization and methylation processes to provide the desired carbazoles, including clausine V. Following an inverse strategy, a new and short total synthesis of glycoborine is also reported.

The development of bulky palladium NHC complexes for the most-challenging cross-coupling reactions

Palladium-catalyzed cross-coupling reactions enable organic chemists to form C-C bonds in targeted positions and under mild conditions. Although phosphine ligands have been intensively researched, in the search for even better cross-coupling catalysts attention has recently turned to the use of N-heterocyclic carbene (NHC) ligands, which form a strong bond to the palladium center. PEPPSI (pyridine-enhanced precatalyst preparation, stabilization, and initiation) palladium precatalysts with bulky NHC ligands have established themselves as successful alternatives to palladium phosphine complexes. This Review shows the success of these species in Suzuki-Miyaura, Negishi, and Stille-Migita cross-couplings as well as in amination and sulfination reactions.

Palladium-Catalyzed Coupling of Functionalized Primary and Secondary Amines with Aryl and Heteroaryl Halides: Two Ligands Suffice in Most Cases

We report our studies on the use of two catalyst systems, based on the ligands BrettPhos (1) and RuPhos (2), which provide the widest scope for Pd-catalyzed C-N cross-coupling reactions to date. Often low catalyst loadings and short reaction times can be used with functionalized aryl and heteroaryl coupling partners. The reactions are highly robust and can be set up and performed without the use of a glovebox. These catalysts should find wide application in the synthesis of complex molecules including pharmaceuticals, natural products and functional materials.