Rosa María Sebastián

Palladium(0) nanoparticles stabilized by phosphorus dendrimers containing coordinating 15-membered triolefinic macrocycles in periphery.

A new family of phosphorus dendrimers containing on their surfaces 3, 6, 12, and 96 15-membered azamacrocycles has been synthesized. The coordinating ability of these macrocycles to palladium(0) atoms allowed the preparation of new dendrimers of several generations containing the corresponding metal complexes and several new nanoparticulated materials, where nanoparticles are stabilized mainly by the complexed dendrimers of the zero, first, and fourth generations. No reduction process of palladium(II) salts was needed to prepare nanoparticles of 2.5-7.9 nm diameter. All the new compounds and materials have been characterized by NMR, IR, elemental analysis and/or matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) spectrometry, high-resolution transmission electron microscopy, and electron diffraction. Also UV-vis spectra were obtained. The Mizoroki-Heck reaction has been catalyzed in a homogeneous and heterogeneous manner by using four different materials; in all cases, the catalyst could be recovered and reused several times.

Phosphine-Free Perfluoro-Tagged Palladium Nanoparticles Supported on Fluorous Silica Gel: Application to the Heck Reaction†

The immobilization of phosphine-free perfluoro-tagged palladium nanoparticles Pd-1 on fluorous silica gel (FSG) and their utilization in the Heck reaction have been investigated. High yields of vinylic substitution products have been obtained. Recycling studies have shown that the solid-supported palladium catalyst can be readily recovered and reused several times without significant loss of activity. Reactions and recovery of the solid-supported palladium catalyst system can be carried out in the presence of air, without any particular precaution.

An Alternative to the Classical α‐Arylation: The Transfer of an Intact 2‐Iodoaryl from ArI(O2CCF3)2

The α-arylation of carbonyl compounds is generally accomplished under basic conditions, both under metal catalysis and via aryl transfer from the diaryl λ(3)-iodanes. Here, we describe an alternative metal-free α-arylation using ArI(O2CCF3)2 as the source of a 2-iodoaryl group. The reaction is applicable to activated ketones, such as α-cyanoketones, and works with substituted aryliodanes. This formal C-H functionalization reaction is thought to proceed through a [3,3] rearrangement of an iodonium enolate. The final α-(2-iodoaryl)ketones are versatile synthetic building blocks.

15-Membered triolefinic macrocycles as stabilizers of palladium(0) nanoparticles

15-Membered triolefinic macrocycles form complexes with palladium(0). However, metal nanoparticles are formed instead of discrete complexes if substituents provided with the ability to stabilize nanoparticles are incorporated into the structure of the macrocycle. Ancillary substituents include fluorous and polyoxyethylenated chains. The role of initial organometallic coordination in the early steps of nanoparticle formation is underlined.

Dimethoxyethane as an Alternative Solvent for Schmidt Reactions. Preparation of Homochiral N-(5-Oxazolyl)oxazolidinones from N-Acetoacetyl Derivatives of Oxazolidinones

Dimethoxyethane is an useful solvent for the Schmidt reaction of ketones and β-ketoesters with sodium azide and methanesulfonic acid to afford amides and amidoesters. This solvent is an alternative to the unsafe chlorinated solvents normally used. A β-diketone and several (4S)-N-(2-alkylacctoacetyl)-4-benzyloxazolidin-2-ones afford oxazoles under those conditions.

Synthesis and structural characterization of a dendrimer model compound based on a cyclotriphosphazene core with TEMPO radicals as substituents.

The synthesis of the 3Gc0T zero generation dendrimer with a cyclotriphosphazene core functionalized with nitroxyl radicals in its six branches has been performed. The radical units have been used as probes to determine the orientation of the six branches in solution experimentally by Electron Paramagnetic Resonance (EPR) spectroscopy compared with the structure obtained in the solid state by X-ray diffraction. The orientation of the dendrimer branches is the same in solution as in the solid state.

The Contribution Made by Triphenylphosphane in the Putative Catalysis by Ruthenium Species in Conjugate Additions of β-Dicarbonyl Compounds

Triphenylphosphane catalyzes conjugate additions of β-dicarbonyl compounds to π-acceptor olefins and dialkyl azodicarboxylates. Formation of quaternary centers at the nucleophiles has been achieved. The catalytic action of tris(triphenylphosphane)ruthenium(II) chloride and tetrakis(triphenylphosphane)ruthenium(II) hydride is at least partially due to the phosphane ligand.

Asymmetric synthesis of quaternary α-amino acids using d-ribonolactone acetonide as chiral auxiliary

Abstract We describe a new simple methodology to prepare enantiopure α,α-dialkylglycines based on the use of commercially available d -ribonolactone as a chiral auxiliary. Enantiopure α-methyl and α-butyl series are prepared through diastereoselective alkylation and subsequent Schmidt rearrangement of α,α-dialkylacetoacetates of d -ribonolactone acetonide. Absolute configuration was assigned through preparation of enantiopure 4,4-disubstituted 3-methyl-2-pyrazolin-5-ones.

DIASTEREOSELECTIVE ALKYLATION OF CHIRAL DERIVATIVES OF ACETOACETIC ACID

Abstract N-acetoacetyl-(S)-4-benzyloxazolidin-2-one and N-acctoacetyl-(R)-bornane-10,2-sultam are alkylated at the C-α of the acctoacetyl moiety with significant diastereoisomeric excesses. The diastereoisomers are in general easily separable and configurationally fairly stable.

Diastereoselective alkylation of 8-phenylmenthyl 2-methylacetoacetate. Preparation of enantiomerically pure 4,4-disubstituted 2-pyrazolin-5-ones

Abstract Aklylation of (1 R ,3 S ,4 S )-8-phenylmenthyl 2-methylacetoacetate with alkyl halides affords 2-alkyl halides affords 2-alkyl-2-methylacetoacetates in diastereomeric ratios 72:28 to 85:15. The major R (at C-α) diastereoisomers are converted into enantiopure 4,4-disubstituted 2-pyrazolin-5-ones with recovery of the chiral inductor.