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

<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%

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 <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

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

P‑Chirogenic Phosphines Supported by Calix[4]arene: New Insight into Palladium-Catalyzed Asymmetric Allylic Substitution

The first P-chirogenic mono- and diphosphine ligands supported on the upper rim of a calix[4]­arene moiety were synthesized using the ephedrine methodology. The lithiated calix[4]­arene mono- and dianions both react with the oxazaphospholidine–borane, prepared from ephedrine, to afford regio- and stereoselectively the corresponding calix[4]­arenyl aminophosphine–boranes, by cleavage of the heterocyclic ring at the P–O bond position. Subsequent reactions with HCl and then organolithium reagent and finally decomplexation with DABCO lead to the corresponding calix[4]­arenyl mono- or diphosphines. Both enantiomers of the calix[4]­arenyl phosphines were obtained either by using (+)- or (−)-ephedrine or by changing the addition order of the organolithium reagents during the synthesis. The enantiomeric excesses of the phosphines were determined either by HPLC on a chiral column of their borane complexes or by ³¹P NMR in the presence of a chiral palladium complex. The absolute configurations of the mono- and diphosphinocalix[4]­arenes were assigned by X-ray analysis of their crystalline borane complexes. The P-chirogenic calix[4]­arenyl phosphines were tested for asymmetric palladium-catalyzed allylic substitution of (<i>E</i>)-1,3-diphenylprop-2-en-1-yl acetate, by dimethyl malonate or benzylamine. When the bis-methylphenylphosphino calix[4]­arene was used, the allylic products were obtained with 82% and 79% ee, respectively. In both cases, the use of a diphosphine affords better results than using 2 equivalents of monophosphine. Despite the <i>C</i>₂ symmetry of the P-chirogenic diphosphine calix[4]­arene ligand, computer modeling of the corresponding Pd­(allyl) complex shows a clear dissymmetry of the LUMO, which is in good agreement with a complexed η¹-allyl moiety and with the regio- and enantioselectivity of the Pd-catalyzed allylations

P‑Chirogenic Phosphines Supported by Calix[4]arene: New Insight into Palladium-Catalyzed Asymmetric Allylic Substitution

The first P-chirogenic mono- and diphosphine ligands supported on the upper rim of a calix[4]­arene moiety were synthesized using the ephedrine methodology. The lithiated calix[4]­arene mono- and dianions both react with the oxazaphospholidine–borane, prepared from ephedrine, to afford regio- and stereoselectively the corresponding calix[4]­arenyl aminophosphine–boranes, by cleavage of the heterocyclic ring at the P–O bond position. Subsequent reactions with HCl and then organolithium reagent and finally decomplexation with DABCO lead to the corresponding calix[4]­arenyl mono- or diphosphines. Both enantiomers of the calix[4]­arenyl phosphines were obtained either by using (+)- or (−)-ephedrine or by changing the addition order of the organolithium reagents during the synthesis. The enantiomeric excesses of the phosphines were determined either by HPLC on a chiral column of their borane complexes or by ³¹P NMR in the presence of a chiral palladium complex. The absolute configurations of the mono- and diphosphinocalix[4]­arenes were assigned by X-ray analysis of their crystalline borane complexes. The P-chirogenic calix[4]­arenyl phosphines were tested for asymmetric palladium-catalyzed allylic substitution of (<i>E</i>)-1,3-diphenylprop-2-en-1-yl acetate, by dimethyl malonate or benzylamine. When the bis-methylphenylphosphino calix[4]­arene was used, the allylic products were obtained with 82% and 79% ee, respectively. In both cases, the use of a diphosphine affords better results than using 2 equivalents of monophosphine. Despite the <i>C</i>₂ symmetry of the P-chirogenic diphosphine calix[4]­arene ligand, computer modeling of the corresponding Pd­(allyl) complex shows a clear dissymmetry of the LUMO, which is in good agreement with a complexed η¹-allyl moiety and with the regio- and enantioselectivity of the Pd-catalyzed allylations