Reaccions de Pauson-Khand amb alcoxialquins derivats d'alcohols quirals

Se han estudiado las reacciones intramoleculares de Pauson-Khand de los eteres 3-alcoxialil propargílicos y 3-alcoxipropargil alílicos derivados del 2-neopentiloxi-3-bornanol y del 3-neopentiloxi-iso-borneol. Las diastereoselectividades observadas en las reacciones de estos sistemas llegó hasta 14/1 (aproximación del inductor unido al alquino). Se ha abordado, también, el estudio de la inducción asimétrica en las reacciones intermoleculares de Pauson-Khand y en este contexto se diseñó y preparó un nuevo tipo de auxiliar quiral quelante. Las reacciones del complejo de dicobaltohexacarbonilo del 10-metiltio-iso-borniloxietino con olefinas tensionadas transcurre con elevada selectividad. En el caso del norbornadieno se llegó al 91% D.E.. En ambas aproximaciones, la intra y la intermolecular, se recuperaron los auxiliares quirales con excelentes rendimientos, y se determinaron las configuraciones absolutas de los respectivos aductos de Pauson-Khand

Reaccions de Pauson-Khand amb alcoxialquins derivats d'alcohols quirals

[spa] Se han estudiado las reacciones intramoleculares de Pauson-Khand de los eteres 3-alcoxialil propargílicos y 3-alcoxipropargil alílicos derivados del 2-neopentiloxi-3-bornanol y del 3-neopentiloxi-iso-borneol. Las diastereoselectividades observadas en las reacciones de estos sistemas llegó hasta 14/1 (aproximación del inductor unido al alquino). Se ha abordado, también, el estudio de la inducción asimétrica en las reacciones intermoleculares de Pauson-Khand y en este contexto se diseñó y preparó un nuevo tipo de auxiliar quiral quelante. Las reacciones del complejo de dicobaltohexacarbonilo del 10-metiltio-iso-borniloxietino con olefinas tensionadas transcurre con elevada selectividad. En el caso del norbornadieno se llegó al 91% D.E.. En ambas aproximaciones, la intra y la intermolecular, se recuperaron los auxiliares quirales con excelentes rendimientos, y se determinaron las configuraciones absolutas de los respectivos aductos de Pauson-Khand

Ethylene glycol assisted intermolecular Pauson-Khand reaction

The use of ethylene glycol as additive in the N-oxide-promoted intermolecular Pauson-Khand reaction (PKR) has been studied. The addition of 15% ethylene glycol to the reaction mixture consistently increased (from 20% up to 2-4-fold) the reaction yield

Enantioselective Synthesis of β-Methyl Amines via Iridium-Catalyzed Asymmetric Hydrogenation of N-Sulfonyl Allyl Amines.

The iridium-catalyzed asym. hydrogenation of several N-sulfonyl allyl amines was reported. All substrates could be easily obtained by the Ir-catalyzed isomerization of N-tosylaziridines reported previously. The com. available threonine-derived phosphinite (UbaPHOX) iridium complex had been found to be the best catalyst for this catalytic application, affording β-Me amines I [R1 = H, 4-Cl, 4-Br, etc.;R2 = Me, i-Pr, 4-MeC6H4; R3 = H, Me] with good to excellent ee values (up to 94%). The synthetic potential of this novel methodol. was demonstrated by the formal synthesis of Lorcaserin and LY-404187

Iridium complexes with P-stereogenic phosphino imidazole ligands: Synthesis, structure and catalysis

The synthesis of optically and diastereomerically pure P-stereogenic phosphine-imidazole ligands is reported. The new ligands contain either a benzoimidazole or a 4-phenylimidazole as a N-donor fragment. The ligands were coordinated to iridium and the structure of the corresponding cationic COD complexes was detd. by x-ray anal. The combination of the chiral phosphorus atom and the imidazole substituents generate a strong chiral environment around the metal center. Preliminary hydrogenation reactions with a model cyclic β-enamide are also reported

P-Stereogenic bisphosphines with a hydrazine backbone: from N-N atropoisomerism to double nitrogen inversion

The synthesis of P-stereogenic bisphosphine ligands starting from a phosphinous acid chiral synthon and hydrazine is reported. The dialkylation of the hydrazine backbone yielded atropo- and nitrogeninversion isomers which are in slow exchange. The crystallization of one of the isomers allowed us to study the reaction kinetics of the equilibria. The new ligands were tested in the Rh catalysed asymmetric hydrogenation of various benchmark substrates attaining up to 99% ee

Coordination chemistry and catalysis with secondary phosphine oxides

Secondary phosphine oxides present a tautomeric equilibrium between the pentavalent oxide form (SPO) and the trivalent phosphinous acid (PA). This dichotomy is the origin of the rich coordination chemistry of this class of compounds. As the pentavalent oxide form usually predominates, SPOs are air-stable but at the same time metal coordination can shift the tautomerism towards the PA form, making the ligand act as an ordinary trivalent phosphine. For this reason this class of ligands have found application in numerous homogeneously catalysed reactions, including some enantioselective transformations. This review aims to give an up to date account on the synthesis, coordination chemistry and homogeneous catalysis with SPOs

Asymmetric intermolecular cobalt-catalyzed Pauson-Khand reaction using a p-stereogenic bis-phosphane

The asymmetric intermolecular and catalytic Pauson-Khand reaction has remained an elusive goal since Khand and Pauson discovered this transformation. Using a novel family of P-stereogenic phosphanes, we developed the first catalytic system with useful levels of enantioselection for the reaction of norbornadiene and trimethylsilylacetylene. The results demonstrate that Co-bisphosphane systems are sufficiently reactive and that they lead to high selectivity in the intermolecular process

Efficient preparation of (S)- and (R)-tert-Butylmethylphosphine-Borane: a novel entry to important P-Stereogenic ligands

A novel one-pot reductive methodol. for the synthesis of optically pure tert-butylmethylphosphine-borane is reported. The prepn. uses as the starting material tert-butylmethylphosphinous acid-borane, which is available in both enantiomeric forms from cis-1,2-aminoindanol and tert-butyldichlorophosphine. The process is based on the redn. of a mixed anhydride, the configurational stability of which has been studied in several solvents and temps. Tetrabutylammonium borohydride was the best reducing agent allowing for the development of a practical process. To demonstrate the utility of the new methodol., the product obtained in this manner was used in the prepn. of Quinox-P*

Rhodium-Catalyzed Pauson−Khand Reaction Using a Small-Bite-Angle P‑Stereogenic C1‑Diphosphine Ligand

The asymmetric Pauson−Khand reaction catalyzed by [Rh(COD)(MaxPHOS)]BF4 is described. Several 1,6-enynes have been chosen as model substrates affording moderate yields and selectivities of up to 86% ee. Besides binap-type ligands, we have demonstrated that the Pstereogenic C1-symmetry small-bite-angle ligand MaxPHOS is a viable ligand in this process. The formation of [2+2+2] cycloaddition compounds has shown to be a competitive process. A mechanism is proposed to account for the observed results. The intermediate rhodium dicarbonyl complex 6 was synthesized, and its solid-state structure was elucidated by X-ray crystallography