Phosphine Catalyzed Michael-Type Additions: The Synthesis of Glutamic Acid Derivatives from Arylidene-α-amino Esters.

The reaction of arylidene-α-amino esters with electrophilic alkenes to yield Michael-type addition compounds is optimized using several phosphines as organocatalysts. The transformation is very complicated due to the generation of several final compounds, including those derived from the 1,3-dipolar cycloadditions. For this reason, the selection of the reaction conditions is a very complex task and the slow addition of the acrylic system is very important to complete the process. The study of the variation in the structural components of the starting imino ester is performed as well as the expansion of other electron-poor alkenes. The crude products have a purity higher than 90% in most cases without any purification. A plausible mechanism is detailed based on the bibliography and the experimental results. The synthesis of pyroglutamate entities, after the reduction of the imino group and cyclization, is performed in high yields. In addition, the hydrolysis of the imino group, under acidic media, represents a direct access to glutamate surrogates.

Mechanistic Study on Allylic Arylation in Water with Linear Polystyrene-Stabilized Pd and PdO Nanoparticles.

The catalytic cycle of allylic arylation in water catalyzed by linear polystyrene-stabilized Pd or PdO nanoparticles (PS-PdNPs or PS-PdONPs) was investigated. Stoichiometric stepwise reactions indicated that the reaction did not proceed stepwise on the surface of the catalyst. In the case of the reaction with PS-PdNPs, the leached Pd species is the catalytically active species and the reaction takes place through a similar reaction pathway accepted in the case of a complex catalyst. In contrast, allylic arylation using PS-PdONPs as a catalyst occurs via a Pd(II) catalytic cycle.

Poly(tetrafluoroethylene)-Stabilized Metal Nanoparticles: Preparation and Evaluation of Catalytic Activity for Suzuki, Heck, and Arene Hydrogenation in Water.

Poly(tetrafluoroethylene)-stabilized Pd nanoparticles (PTFE-PdNPs) were prepared in water with 4-methylphenylboronic acid as a reductant and characterized using powder X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Small PdNPs with a fairly uniform size were obtained in the presence of PTFE, whereas aggregation of palladium was observed in the absence of PTFE. PTFE-PdNPs showed high catalytic activity for the Suzuki coupling reaction in water and were reused without any loss of activity. No palladium species were observed by ICP-AES analysis in the reaction solution after the reaction, nor was any change in particle size observed after the recycle experiment. PTFE-PdNPs also exhibited excellent catalytic activity and reusability for the Heck reaction in water. Although palladium species were not detected in the reaction solution after the reaction, aggregates and smaller sizes of PdNPs were observed in the TEM image of the recovered catalyst. PTFE was also useful as the stabilizer of rhodium nanoparticles (RhNPs) prepared by reduction with NaBH4. PTFE-RhNPs showed high catalytic activity and reusability toward arene hydrogenation under mild conditions.