El rechazo entre iguales: una visión general

III Jornadas Internacionales del Grupo GREIHablar de aceptación y rechazo entre iguales es un tema de gran relevancia en nuestro contexto social actual. Este hecho es consecuencia de la importancia que tiene la atracción interpersonal como índice de adaptación socioemocional, ya que la realidad evidencia que una buena aceptación en el grupo de compañeros y compañeras favorece una buena adaptación y bienestar socioemocional, mientras que niveles bajos de aceptación social son factores de riesgo y de problemática en el tema de interacción socialAcceptance and rejection between peers have become a relevant issue in our current social context. This is a consequence of the importance that interpersonal attraction is bestowed as a socio-emotional adaptation system. Indeed, as reality evidences, strong acceptance levels among peers foster not only better adaptation within the group but also better levels of socio-emotional well-being. However, low social acceptance levels stand as problematic risk factors regarding social interaction

Stereoselective Synthesis of Unsaturated and Functionalized l‑NHBoc Amino Acids, Using Wittig Reaction under Mild Phase-Transfer Conditions

The stereoselective synthesis of a new amino acid phosphonium salt was described by quaternization of melting triphenylphosphine with the γ-iodo NHBoc-amino ester, derived from l-aspartic acid. The deprotection of the carboxylic acid function to afford the phosphonium salt with a free carboxylic acid group was achieved by a palladium-catalyzed desallylation reaction. This phosphonium salt was used in the Wittig reaction with aromatic or aliphatic aldehydes and trifluoroacetophenone, under solid–liquid phase-transfer conditions in chlorobenzene and in the presence of K₃PO₄ as weak base, to afford the corresponding unsaturated amino acids without racemization. Thus, the reaction with substituted aldehydes allows to graft various functionalized groups on the lateral chain of the amino acid, such as trifluoromethyl, cyano, nitro, ferrocenyl, boronato, or azido. In addition, the reaction of the amino acid Wittig reagent with α,β-unsaturated aldehydes leads to amino acids bearing a diene on the lateral chain. Finally, this amino acid phosphonium salt appears to be a new powerful tool for the preparation of unsaturated and non-proteinogenic α-amino acids, directly usable for the synthesis of customized peptides

Organometallic Oligomers Based on Bis(arylacetylide)bis(P-chirogenic phosphine)platinum(II) Complexes: Synthesis and Photonic Properties

A series of P-chirogenic oligomers of the type (CC<b>aryl</b>CCPtL₂)<i>_n</i> [L = (<i>R</i>)- and (<i>S</i>)-P­(Ph)­(<i>i</i>Pr)­(C₁₇H₃₅); <b>aryl</b> = 1,4-benzene, 2,1,3-benzothiadiazole] along the corresponding achiral analogues (L = PBu₃) and model complexes PhCCPtL₂CCPh were prepared from the ephedrine strategy and were fully characterized [¹H, ³¹P NMR; IR; small-angle X-ray scattering (SAXS); gel permeation chromatography (GPC); thermal gravimetric analysis (TGA); circular dichroism, UV–vis, and luminescence spectroscopy; photophysics, and degree of anisotropy measurements]. From the CD measurements, the chiral environment of the phosphine ligands is modestly felt by the aryl moieties. Concurrently, the TGA shows that the P­(C₁₇H₃₅)­(Ph)­(<i>i</i>-Pr)-containing materials are more stable than those containing the shorter chain ligand PBu₃, and exhibits red-shifted absorption and emission bands compared to those including the PBu₃ ligands. The presence of the long chain on the phosphorus atoms does not greatly alter the photophysical parameters, notably the emission lifetimes, and fast triplet energy transfer terminal* → central unit has been deduced from the absence of luminescence arising from the terminal units

<i>o</i>‑(Hydroxyalkyl)phenyl P‑Chirogenic Phosphines as Functional Chiral Lewis Bases

The stereoselective synthesis of P-chirogenic phosphines bearing an <i>o</i>-hydroxyalkyl chelating arm is described. The synthesis is based either on the hydroxyalkylation of P-chirogenic <i>o</i>-bromophenylphosphines (borane) or on their carbonatation and then reduction. The hydroxyalkylation with benzaldehyde or pivalaldehyde affords a mixture of epimers which are isolated by chromatography and characterized by their X-ray structures. Preliminary assays of free P-chirogenic <i>o</i>-(hydroxyalkyl)phenyl phosphines, as new functional Lewis bases in catalyzed asymmetric aza-MBH reaction, lead to β-aminoester derivatives with ee values up to 74%

Modular <i>P</i>‑Chirogenic Phosphine-Sulfide Ligands: Clear Evidence for Both Electronic Effect and <i>P</i>‑Chirality Driving Enantioselectivity in Palladium-Catalyzed Allylations

Using the ephedrine methodology, modular stereoselective syntheses of a new class of <i>P</i>-chirogenic phosphines bearing a sulfur-chelating arm (P*,S-hybrid ligand) are described. A first series of syntheses based on a Fries-like rearrangement of <i>P</i>-chirogenic phosphinite-boranes, which are prepared from 2-bromobenzyl or 2-bromophenethyl alcohol and are mediated by metal–halide exchange, have been performed. This rearrangement affords phosphine-boranes stereospecifically with an <i>o</i>-hydroxy­alkylphenyl substituent. The latter residue is subsequently converted into a sulfur-containing group. In a second series, the stereoselective syntheses were achieved according to a new strategy involving a reaction of a thiophenyllithium reagent with a <i>P</i>-chirogenic phosphinite. The X-ray structures of the P*,S ligands and their palladium complexes allow us to address the absolute configuration at both the phosphorus and sulfur centers. The P*,S ligands were used in palladium-catalyzed allylic alkylations, as tests, affording asymmetric inductions up to 96% ee. Computer modeling corroborates the regio- and enantioselectivity of the Pd-catalyzed allylations and the low influence of the substituent carried by the sulfur moiety, particularly when the chelate forms a six-membered ring with the metal

Stereoselective Synthesis of P-Chirogenic Dibenzophosphole–Boranes via Aryne Intermediates

A new aryne-mediated tandem cross-coupling/P-cyclization sequence starting from tertiary phosphine–boranes and 1,2-dibromobenzenes is reported. P-chirogenic dibenzophospholes become accessible in a regio-, chemo-, and diastereoselective way

<i>o</i>‑(Hydroxyalkyl)phenyl P‑Chirogenic Phosphines as Functional Chiral Lewis Bases

The stereoselective synthesis of P-chirogenic phosphines bearing an <i>o</i>-hydroxyalkyl chelating arm is described. The synthesis is based either on the hydroxyalkylation of P-chirogenic <i>o</i>-bromophenylphosphines (borane) or on their carbonatation and then reduction. The hydroxyalkylation with benzaldehyde or pivalaldehyde affords a mixture of epimers which are isolated by chromatography and characterized by their X-ray structures. Preliminary assays of free P-chirogenic <i>o</i>-(hydroxyalkyl)phenyl phosphines, as new functional Lewis bases in catalyzed asymmetric aza-MBH reaction, lead to β-aminoester derivatives with ee values up to 74%

Efficient Synthesis of (P-Chirogenic) <i>o</i>‑Boronated Phosphines from <i>sec</i>-Phosphine Boranes

An efficient synthesis of boronated phosphines with an <i>o</i>-phenylene-bridge prepared from <i>sec</i>-phosphine boranes and using benzyne chemistry is reported. Successive reactions of <i>sec</i>-phosphine boranes with <i>n</i>-BuLi and 1,2-dibromobenzene, and then with boron reagents, afford the <i>o</i>-boronato­phenyl­phosphine derivatives in 71% yields. The use of P-chirogenic <i>sec</i>-phosphine boranes leads to the free boronated phosphines with retention of configuration at the P-center after decomplexation. The reaction of P-chirogenic <i>o</i>-boronato­phenyl­phosphine with KHF₂ affords the corresponding trifluoroborated phosphine with ee >98%

Modular Phosphole-Methano-Bridged-Phosphine(Borane) Ligands. Application to Rhodium-Catalyzed Reactions

The synthesis of the phospholyl­(phosphinoborane)­methane air- and moisture-stable hybrid ligands <b>4a</b>–<b>f</b>, starting from 1-phenylphospholes <b>1a</b>–<b>d</b>, was performed via P–C bond coupling on the methano bridge. Two strategies were investigated, according to the phospholyl moiety used as a nucleophilic or an electrophilic reagent. In the first pathway, the phospholyl anions react with the easily available (chloromethyl)­diphenylphosphine–borane <b>3</b> to afford ligands <b>4a</b>–<b>d</b> in 29–67% isolated yields. In the second pathway, the phospholyl­(dicyclohexylphosphinoborane)­methane ligands <b>4e</b>,<b>f</b> were synthesized in 18–23% yields, through a nucleophilic substitution on the cyanophosphole. Removal of the BH₃ moiety on <b>4a</b>–<b>c</b> assisted by DABCO leads to the hybrid phospholyl­(diphenylphosphino)­methanes <b>5a</b>–<b>c</b>. Compounds <b>4</b> and <b>5</b> were fully characterized by multinuclear NMR spectroscopy (¹H, ³¹P, ¹³C, ¹¹B), mass spectrometry, and elemental analysis, and the X-ray crystal structures of <b>4a</b>,<b>c</b> and <b>5a</b>,<b>b</b> have been established. Ligands <b>5a</b>,<b>b</b> were used to prepare the cationic rhodium complexes [Rh­(η⁴-COD)­(<b>5a</b>)]⁺ (<b>8a′</b>), [Rh­(η⁴-COD)­(<b>5b</b>)]⁺ (<b>8b</b>), [Rh­(<b>5a</b>)₂]⁺ (<b>9a′</b>), and [Rh­(<b>5b</b>)₂]⁺ (<b>9b</b>), containing four-membered chelate rings with BF₄^– or CF₃SO₃^– as counterions. Ligands <b>4a</b>–<b>f</b> were also used to synthesize the [Rh­(η⁴-COD)­(<b>4</b>)]⁺ chelate complexes <b>10a</b>–<b>f</b>, resulting from coordination of the phospholyl part and the BH₃ group via a η² mode with two bridging B–H–Rh 3c–2e bonds, as shown by the X-ray crystal structures of the complexes <b>10b</b>,<b>c</b>. Rhodium complexes <b>8</b> and <b>10</b> isolated or formed in situ with ligands <b>4</b> and <b>5</b> were studied for catalytic hydrogenation of methyl 2-(acetamidomethyl)­acrylate (<b>11</b>) and hydroboration of styrene (<b>13</b>) with catecholborane. In both reactions, the catalytic systems prepared either from the phospholyl­(phosphinoborane)­methane ligands <b>4</b> or the corresponding free ligands <b>5</b>, gave good to excellent conversions. In addition, the regioselectivity of the catalyzed hydroboration is slightly influenced using these ligands. Finally, the use of hybrid phospholyl­(phosphinoborane)­methanes as ligands offers a new, efficient way to improve catalytic processes, for designing both the structure and the electronic properties of the catalyst, or still to implement it without removing the borane protecting group

<i>o</i>‑Boronato- and <i>o</i>‑Trifluoroborato–Phosphonium Salts Supported by l‑α-Amino Acid Side Chain

The synthesis of <i>o</i>-boronato- and <i>o</i>-trifluoroborato–phosphonium salts supported by the l-amino acid side chain is described. The synthesis of these new class of amino acid derivatives was achieved by stereoselective quaternization of <i>o</i>-(pinacolato)­boronatophenylphosphine with β- or γ-iodo amino acid derivatives which are prepared from l-serine or l-aspartic acid, respectively. The quaternization of the phosphine was performed using either iodo amino ester or carboxylic acid derivatives. In addition, free carboxylic acid and amine derivatives were obtained by saponification or HCl acidolysis of <i>o</i>-boronato–phosphonium amino esters, respectively. The usefulness of these compounds in peptide coupling was demonstrated by coupling an <i>o</i>-boronato–phosphonium amino ester with an aspartic acid moiety. When the <i>o</i>-boronato–phosphonium amino acid or dipeptide derivatives were mixed with fluoride, the corresponding <i>o</i>-trifluoroborated products were cleanly and rapidly obtained in high isolated yields. The hydrolysis of these compounds at room temperature using a phosphate buffer pH 7/CD₃CN mixture has shown only traces of free fluoride F^– after several days. Finally, a preliminary radiolabeling essay has proven the facile [¹⁸F]-fluoride incorporation and high stability of the radiolabeled product in aqueous conditions. Indeed, this new class of boron–phosphonium amino acid derivatives shows promising properties for their applications in synthesis and labeling of peptides