Elisabet Duñach

Direct and catalytic synthesis of quinoxaline derivatives from epoxides and ene-1,2-diamines

We describe here a new synthesis of quinoxaline derivatives by a Bi-catalyzed oxidative coupling of epoxides and ene-1,2-diamines.

Metal triflimidates: better than metal triflates as catalysts in organic synthesis--the effect of a highly delocalized counteranion.

The continuously increasing need for novel and selective methods in organic synthesis to aid drug discovery and to address environmental concerns is a constant source of stimulation to develop novel and more efficient reaction systems. This has often resulted in a focus on transition metals, ligands, and additives, with much less attention paid to the counterion(s) of the metal cation. Recently, metal salts with one or more triflimidate counterion(s) have appeared as a unique class of catalysts that display outstanding σ- and π-Lewis acid character. The highly delocalized nature of the triflimidate counterion, combined with its high steric hindrance results in virtually no nucleophilic behavior and an extremely high positive charge density on the metal cation, thus enhancing its Lewis acid character. Consequently, these metal triflimidates often outperform their metal halide or triflate analogues. This Review describes general methods for the preparation of metal triflimidate salts and their use as catalysts.

Catalytic Versatility and Backups in Enzyme Active Sites: The Case of Serum Paraoxonase 1

The origins of enzyme specificity are well established. However, the molecular details underlying the ability of a single active site to promiscuously bind different substrates and catalyze different reactions remain largely unknown. To better understand the molecular basis of enzyme promiscuity, we studied the mammalian serum paraoxonase 1 (PON1) whose native substrates are lipophilic lactones. We describe the crystal structures of PON1 at a catalytically relevant pH and of its complex with a lactone analogue. The various PON1 structures and the analysis of active-site mutants guided the generation of docking models of the various substrates and their reaction intermediates. The models suggest that promiscuity is driven by coincidental overlaps between the reactive intermediate for the native lactonase reaction and the ground and/or intermediate states of the promiscuous reactions. This overlap is also enabled by different active-site conformations: the lactonase activity utilizes one active-site conformation whereas the promiscuous phosphotriesterase activity utilizes another. The hydrolysis of phosphotriesters, and of the aromatic lactone dihydrocoumarin, is also driven by an alternative catalytic mode that uses only a subset of the active-site residues utilized for lactone hydrolysis. Indeed, PON1s active site shows a remarkable level of networking and versatility whereby multiple residues share the same task and individual active-site residues perform multiple tasks (e.g., binding the catalytic calcium and activating the hydrolytic water). Overall, the coexistence of multiple conformations and alternative catalytic modes within the same active site underlines PON1s promiscuity and evolutionary potential.

Electrochemical carboxylation of terminal alkynes catalyzed by nickel complexes: unusual regioselectivity

Abstract The electrochemical reduction of the nickel (II) complex Ni(bipy)3(BF4)2 yields an active catalyst for the regioselective functionalization of the 2-position of terminal alkynes with carbon dioxide. A series of α-substituted acrylic acids have been obtained with selectivities of 65–90% and fair overall yields.

Regioselective indium(III) trifluoromethanesulfonate-catalyzed hydrothiolation of non-activated olefins.

Indium(III) trifluoromethanesulfonate was found to be an excellent catalyst for the highly regioselective intra- and intermolecular addition of thiols to non-activated olefins and could be recycled and reused without loss of activity.

Triflic acid-catalysed cyclisation of unsaturated alcohols

In the presence of a catalytic amount of trifluoromethanesulfonic acid, substituted tetrahydrofurans and tetrahydropyrans have been efficiently and selectively obtained from the corresponding unsaturated alcohols.

Electrochemical intramolecular reductive cyclisation catalysed by electrogenerated Ni(cyclam)2

The intramolecular cyclisation of a series of o-halogenated aromatic compounds containing unsaturated side-chains has been developed using electrosynthesis, combined with organometallic catalysis by Ni(cyclam)Br2.

Bi(OTf)3-Catalyzed Cycloisomerization of Aryl-Allenes

Intramolecular hydroarylation of allenes was achieved under very mild conditions using bismuth(III) triflate as the catalyst. Efficient functionalization of activated and nonactivated aromatic nuclei led to C-C bond formation through a formal Ar-H activation. A tandem bis-hydroarylation of the allene moiety was also developed giving access to various interesting polycyclic structures.

An Opportunity for Mg-Catalyzed Grignard-Type Reactions: Direct Coupling of Benzylic Halides with Pinacolborane with 10 mol % of Magnesium

Mg in catalytic amounts as the only metal permits the reductive coupling between benzyl halides and pinacolborane. HBpin acts both as an electrophile and as a reducing agent to regenerate an organomagnesium species in situ. An hydride oxidation mechanism is proposed on the basis of DFT calculations.

Novel electrosynthesis of metallic bis(trifluoromethanesulfonyl) imides

The preparation of a series of bis(trifluoromethanesulfonyl) imide salts of various metals was effected in good yields, under clean, mild and anhydrous conditions, by using a simple electrochemical methodology.