Eleuterio Álvarez

Regioselective Formation of 2,5-Disubstituted Oxazoles Via Copper(I)-Catalyzed Cycloaddition of Acyl Azides and 1-Alkynes

The reaction of 1-alkynes with acyl azides in the presence of [Tpm(*,Br)Cu(NCMe)]BF(4) [Tpm(*,Br) = tris(3,5-dimethyl-4-bromopyrazolyl)methane] as the catalyst provides 2,5-oxazoles in moderate to high yields. This is a novel transformation of the CuAAC type that constitutes a significant variation of the commonly observed [3 + 2] cycloaddition reaction to yield 1,2,3-triazoles.

Use of Hemilabile N,N Ligands in Nitrogen‐Directed Iridium‐Catalyzed Borylations of Arenes

We thank the Spanish “Ministerio de Ciencia e Innovacion” (grants CTQ2010-15297 and CTQ2010-14974, and fellowship to B.E.), the European FEDER funds and the Junta de Andalucia (grants 2008/FQM-3833 and 2009/FQM-4537) for financial support. A.R. thanks the EU for a Marie Curie Reintegration Grant (FP7-PEOPLE-2009-RG-256461) and R.L.-R. thanks CSIC for a JAE predoctoral fellowship.

Phosphino hydrazones as suitable ligands in the asymmetric Suzuki-Miyaura cross-coupling

Phosphino hydrazones derived from C(2)-symmetric hydrazines exhibit excellent catalytic activity and provide good enantioselectivities in the asymmetric Suzuki-Miyaura cross-coupling to axially chiral biaryls, in particular for the most challenging reactions of monocyclic, functionalized aryl bromides and triflates. X-ray analysis of preformed [Pd(P/N)Cl(2)] precatalysts [(P/N) = phosphino hydrazone] revealed a strong n-π conjugation in the hydrazone moiety, identified by a high planarity degree at the pyrrolidine N(sp(3)) atom, that makes rotations around N-N bonds inconsequential. The complexes are also characterized by an envelope-like conformation with the Pd atom placed at the opposite side to the 2-phenyl group on the nearest stereogenic center of the pyrrolidine group. The isolation and structural analysis of oxidative addition intermediates indicate that the configurational stability of Pd-C(Ar) bonds is dependent on the substitution pattern in the aryl bromide.

Asymmetric formal carbonyl-ene reactions of formaldehyde tert -butyl hydrazone with α-keto esters: Dual activation by bis-urea catalysts

The dual activation of α-keto esters and formaldehyde tert-butyl hydrazone by BINAM-derived bis-ureas is the key to achieve high reactivity and excellent enantioselectivities in nucleophilic addition (formal carbonyl-ene reaction) to functionalized tertiary carbinols. Ensuing high-yielding diazene-to-aldehyde tranformations and subsequent derivatizations provides a direct entry to a variety of densely functionalized products.

Selective Synthesis of N-Substituted 1,2-Dihydropyridines from Furans by Copper-Induced Concurrent Tandem Catalysis

A novel transformation in which mono- or dialkyl-substituted furans are converted into 1,2-dihydropyridines upon reaction with PhI horizontal lineNTs at room temperature is reported. The reaction is catalyzed by complexes of general formula Tp(x)M (M = Cu, Ag) and consists of a one-pot procedure with four consecutive catalytic cycles. Furan aziridination is followed by aziridine ring-opening, transimination reaction, inverse-electronic-demand aza-Diels-Alder reaction, and a final hydrogen elimination reaction. The mechanism of the overall transformation is proposed where the metal complex displays a crucial role along the reaction pathway.

Hydrogenation of imines catalysed by ruthenium(II) complexes based on lutidine-derived CNC pincer ligands.

The preparation of new Ru(II) complexes incorporating fac-coordinated lutidine-derived CNC ligands is reported. These derivatives are selectively deprotonated by (t)BuOK at one of the methylene arms of the pincer, leading to catalytically active species in the hydrogenation of imines.

Isoquinolin-1-ylidenes as electronically tuneable ligands

The novel isoquinolin-1-ylidene ligands, introduced into Rh(I) complexes by exploiting the carbene-like reactivity of adducts , exhibit ligand properties similar to those of classic NHCs, and their electronic properties can be tuned by the introduction of electron-withdrawing or donating groups in the benzene ring.

A concise synthesis of ortho-condensed oxane-oxene, oxepene, oxocene and oxonene ring systems

Abstract An efficient strategy for the synthesis of trans -fused oxabicyclic systems involving thioannulation followed by a Ramberg-Backlund olefination as the key step is described.

Olefin epoxidation by hydrogen peroxide catalysed by molybdenum complexes in ionic liquids and structural characterisation of the proposed intermediate dioxoperoxomolybdenum species

The complex [Mo(4)O(16)(dmpz)(6)] (1) has been isolated as part of a study of oxodiperoxomolybdenum catalysed epoxidation of olefin substrates with hydrogen peroxide in ionic liquids. Notably, 1 is the first dioxoperoxomolybdenum species to be structurally characterised.

New insights into the mechanism of oxodiperoxomolybdenum catalysed olefin epoxidation and the crystal structures of several oxo–peroxo molybdenum complexes

[Mo(O)(O(2))(2)(L)(2)] compounds (L = pz, pyrazole; dmpz, 3,5-dimethylpyrazole) were reacted stoichiometrically, in the absence of an oxidant, with cis-cyclooctene in an ionic liquid medium where selective formation of the corresponding epoxide was observed. However, this oxo-transfer reaction was not observed for some other olefins, suggesting that alternative reaction pathways exist for these epoxidation processes. Subsequently, DFT studies investigating the oxodiperoxomolybdenum catalysed epoxidation model reaction for ethylene with hydrogen peroxide oxidant were performed. The well known Sharpless mechanism was first analysed for the [Mo(O)(O(2))(2)(dmpz)(2)] model catalyst and a low energy reaction pathway was found, which fits well with the observed experimental results for cis-cyclooctene. The structural parameters of the computed dioxoperoxo intermediate [Mo(O)(2)(O(2))(dmpz)(2)] in the Sharpless mechanism compare well with those found for the same moiety within the [Mo(4)O(16)(dmpz)(6)] complex, for which the full X-ray report is presented here. A second mechanism for the model epoxidation reaction was theoretically investigated in order to clarify why some olefins, which do not react stoichiometrically in the absence of an oxidant, showed low level conversions in catalytic conditions. A Thiel-type mechanism, in which the oxidant activation occurs prior to the oxo-transfer step, was considered. The olefin attack of the hydroperoxide ligand formed upon activation of hydrogen peroxide with the [Mo(O)(O(2))(2)(dmpz)(2)] model catalyst was not possible to model. The presence of two dmpz ligands coordinated to the molybdenum centre prevented the olefin attack for steric reasons. However, a low energy reaction pathway was identified for the [Mo(O)(O(2))(2)(dmpz)] catalyst, which can be formed from [Mo(O)(2)(O(2))(dmpz)(2)] by ligand dissociation. Both mechanisms, Sharpless- and Thiel-type, were found to display comparable energy barriers and both are accessible alternative pathways in the oxodiperoxomolybdenum catalysed olefin epoxidation. Additionally, the molecular structures of [Mo(O)(O(2))(2)(H(2)O)(pz)] and [Hdmpz](4)[Mo(8)O(22)(O(2))(4)(dmpz)(2)]·2H(2)O and the full X-ray report of [Mo(O)(O(2))(2)(pz)(2)] are also presented.