Diego A. Alonso

Oxime-derived palladacycles as source of palladium nanoparticles

Oxime-derived palladacycles are very efficient and versatile pre-catalysts for a wide range of carbon-carbon bond coupling reactions in air, under very low loading conditions, and employing reagent-grade chemicals. This tutorial review presents the main achievements, advantages and limitations of oxime palladacycles as a source of highly active palladium nanoparticles for high-turnover catalyzed Heck, as well as other homo- and cross-coupling reactions usually carried out employing organic or aqueous solvents. Comparison with other ligandless Pd(II) catalysts is also presented. Recent advances to develop supported oxime-derived palladacycles in order to facilitate precatalyst recovery and reuse in cross-coupling reactions, especially under aqueous reaction conditions, are also discussed.

Transition-Metal-Catalyzed Synthesis of Hydroxylated Arenes

An overview of the recent bibliography in the transition-metal-catalyzed hydroxylation of aryl derivatives is presented. Two reaction protocols are considered: 1) C--H activation/hydroxylation and, 2) cross-coupling hydroxylation of aryl halides. The achievements and limitations for both procedures are described taking into consideration different metal catalyst/oxidant combinations.

A copper- and amine-free Sonogashira-type coupling procedure catalyzed by oxime palladacycles

Abstract Oxime palladacycle derived from 4,4′-dichlorobenzophenone was found to promote the Sonogashira reaction of aryl iodides and aryl bromides with terminal acetylenes using 1 equivalent of tetrabutylammonium acetate in organic solvents generally in 1 h at 110°C and in high TONs (up to 72000).

Chiral 2-Aminobenzimidazoles as Recoverable Organocatalysts for the Addition of 1,3-Dicarbonyl Compounds to Nitroalkenes†

Chiral trans-cyclohexanediamine-benzimidazole organocatalysts promote the conjugate addition of a wide variety of 1,3-dicarbonyl compounds such as malonates, ketoesters, and 1,3-diketones to nitroolefins in the presence of TFA as cocatalyst in toluene as solvent at rt or 0 degrees C. The Michael adducts are obtained in high yield and enantioselectivity, using the chiral 2-aminobenzimidazole 7b as hydrogen-bond-mediated chiral organocatalyst. This catalyst can be recovered by acid-base extractive workup in 94% yield. The proposed bifunctional Brønsted acid-base activation role of the catalyst and the origin of the stereoselectivity of the process is in agreement with DFT calculations. According to these calculations, the protonated tertiary amine from the cyclohexanediamine backbond activates the nitroolefin, while the benzimidazole unit activates the 1,3-dicarbonyl nucleophile.

Oxime‐Derived Palladium Complexes as Very Efficient Catalysts for the Heck–Mizoroki Reaction

Oxime-derived, chloro-bridged palladacycles 16 are efficient complexes for the Heck vinylation of aryl halides. The isolated catalysts are thermally stable, not sensitive to air or moisture and easily accessible from inexpensive starting materials. The reaction can be performed under aerobic conditions, with aryl iodides, bromides and chlorides with acrylic esters and olefins displaying turnover numbers (TON) of up to 1010 for phenyl iodide and turnover frequencies (TOF) of 1.4×108 h−1. Deactivated aryl bromides undergo the Heck reaction with styrene with TON and TOF values up to 97,000 and 6063 h−1, respectively. Even aryl chlorides undergo the coupling reaction with olefins with TON up to 920. Complexes 16 catalyze the synthesis of 2,3-disubstituted indenones and indoles in good yields via annulation reaction of internal alkynes with o-bromo- or o-chlorobenzaldehyde and o-iodoaniline, respectively.

Remote Dipole Effects as a Means to Accelerate [Ru(amino alcohol)]-Catalyzed Transfer Hydrogenation of Ketones

A new generation of 2-aza-norbornyl amino alcohol ligands for the catalytic transfer hydrogenation reaction of aromatic ketones was synthesized. Extremely active catalysts were formed by introducing a ketal functionality at the rear end of the ligand. Acetophenone was reduced in 96% ee at low catalyst loading, substrate to catalyst ratio, S/C 5000, within 90 minutes with isopropyl alcohol as the hydrogen donor. It was found that the dioxolane substituent in the ligand increased the turnover frequency, TOF50, from 1050 h(-1) to 3000 h(-1) at an S/C ratio of 1000. Introduction of a methyl group at the carbinol carbon resulted in TOF50 as high as 8500 h(-1). Transfer hydrogenation of a range of aromatic ketones was evaluated and found to reach completion within 30 minutes at room temperature, and excellent enantioselectivity, up to 99 % ee, was obtained. A possible explanation for the enhanced activity was provided by density functional calculations, which showed that the presence of a remote dipole in the ligand lowered the transition state energy.

Preparation and evaluation of nitrene precursors (PhI=NSO2Ar) for the copper-catalyzed aziridination of olefins

The preparation of different [N-(arenesulfonyl)imino]phenyliodinanes is described along with an evaluation of their utility as nitrene precursors for the copper-catalyzed aziridination of different ...

Simple, economical and environmentally friendly sulfone synthesis

Chemoselective sulfur oxidation of functionalized sulfides was developed using catalytic amounts of MnSO4·H2O (1 mol%) and 30% H2O2 in the presence of a buffer solution of NaHCO3. Aromatic and aliphatic sulfides were oxidized to sulfones in quantitative yields in 15 min. Different functional groups including double bonds, alcohols, ethers of THP and TBDMS groups were tolerated under these mild and green reaction conditions.

Readily available nitrene precursors increase the scope of Evans' asymmetric aziridination of olefins

The performance of the copper-catalyzed asymmetric aziridination of olefins is highly dependent on the properties of the nitrene precursor. Our preliminary results show significant improvements of ...

Recyclable silica-supported prolinamide organocatalysts for direct asymmetric Aldol reaction in water

Asymmetric organocatalytic materials based on a prolinamide scaffold have been synthesized according to different synthetic routes from a monosilylated precursor: simple or surfactant-assisted co-condensation and grafting on preformed mesostructured silica. The catalytic properties of these materials have been compared for direct asymmetric aldol reactions. The best catalytic material results from a simple co-condensation without structure-directing agent. Simple and green conditions are used for the aldol reaction, the process being performed in water at room temperature, with relatively low amounts of supported organocatalysts and in the absence of an acid co-catalyst. Good recyclabilities are observed without the need for catalyst regeneration, with enantioselectivities (ee up to 92%) higher than that of the parent homogeneous catalysts.