Elena Díez

Axially chiral triazoloisoquinolin-3-ylidene ligands in gold(I)-catalyzed asymmetric intermolecular (4 + 2) cycloadditions of allenamides and dienes.

The first highly enantioselective intermolecular (4 + 2) cycloaddition between allenes and dienes is reported. The reaction provides good yields of optically active cyclohexenes featuring diverse substitution patterns and up to three stereocenters. Key to the success of the process is the use of newly designed axially chiral N-heterocyclic carbene-gold catalysts.

Butane-2,3-Diacetal-Desymmetrized Glycolic Acid—A New Building Block for the Stereoselective Synthesis of Enantiopureα-Hydroxy Acids

According to a chiral memory protocol, a chiral glycolic acid equivalent, the butane-2,3-diacetal-desymmetrized glycolate 2, is obtained from chiral 3-halopropane-1,2-diols 1. Compound 2 is a new and effective building block for the synthesis of mono- and dialkylated α-hydroxy acids 3, which constitute a biologically and pharmacologically important structural motif.

Synthesis of Enantiopureα-Alkoxy-α-Trifluoromethyl Aldehydes and Carboxylic Acids from Trifluoromethyl Ketones

Formaldehyde dialkylhydrazones behave as neutral d1 synthons in their uncatalyzed reaction with trifluoromethyl ketones (see reaction). Both racemic and optically pure 1,2-adducts were obtained in good yields. Efficient deprotection of the hydrazone moiety afforded interesting fluorinated quaternary compounds such as 1 and 2.

Direct Synthesis of Dithioketals from N,N-Dialkylhydrazones

Abstract Direct dithioketalisation of N , N -dialkylhydrazones promoted by BF 3 ·Et 2 O or p -TsOH and 1,2-ethanedithiol in dry medium affords the corresponding dithiolanes in nearly quantitative yields. A variety of hydrazones derived from several kinds of aldehydes (aliphatic, aromatic, and α,β-unsaturated) and hydrazines [ N , N -dimethylhydrazine, 1-aminopyrrolidine, and ( S )-1-amino-2-(methoxymethyl)pyrrolidine (SAMP)] were reacted, indicating the generality of the method. The reaction was demonstrated to proceed without racemization of a particularly sensitive chiral substrate.

Synthese von enantiomerenreinen α‐Alkoxy‐ α‐trifluormethylaldehyden und ‐carbonsäuren aus Trifluormethylketonen

Formaldehyd-dialkylhydrazone sind die d1-Reagentien der Wahl, um aus Trifluormethylketonen ohne Katalysatorbeigabe die 1,2-Addukte zu erhalten (siehe Schema). Sowohl racemische als auch optisch reine Derivate waren in guten Ausbeuten zuganglich. Die effektive Abspaltung der Hydrazon-Schutzgruppe fuhrte zu interessanten fluorierten Verbindungen wie 1 und 2.

Asymmetric synthesis of γ-cyano silyl enol ethers

Abstract The selective oxidative cleavage of the SAMP-hydrazone moiety of 4-silyloxy-3-enal hydrazones 6 , leading to the corresponding 4-silyloxy-3-alkenenitriles 7 , is reported. A clean, good yielding transformation was observed when m -CPBA in CH 2 Cl 2 was used as the oxidant, the presence of suspended solid NaHCO 3 being essential in preventing hydrolysis of the silyl enol ether moiety. Use of magnesium monoperoxyphthalate (MMPP) led to over-oxidated products, while hydrogen peroxide, in the presence of catalytic methyltrioxorhenium (MTO), was ineffective. Independent measurements of the enantiomeric excesses for compounds 7 demonstrated the absence of racemization during the process.

N-Heterotricyclic cationic carbene ligands. Synthesis, reactivity and coordination chemistry

The direct dialkylation of triazolo[4,3-b]isoquinolin-3-ylidene structures readily affords dicationic N-heterotricyclic azolium salts. These are suitable starting materials for the synthesis of transition metal complexes containing N-heterotricyclic, cationic ligands characterized by extended charge delocalization. Silver and gold complexes as well as mono- and dicationic rhodium(i) complexes have been prepared and characterized, and the electronic properties of the ligand have been evaluated by using the TEP parameter and by comparison with a non-cationic analogue. X-Ray diffraction analysis of several carbene-metal complexes shows a negligible effect of the charge on the structures of the complexes. The catalytic activity of a tricationic gold complex has been evaluated in the intramolecular hydroarylation of a terminal alkyne.

Synthesis of 2‐Alkyl‐5‐aryl‐1,3,4‐oxadiazolines from N‐Acylhydrazones.

The base-promoted reaction is proposed to proceed through N-acyliminium intermediates to form oxadiazoles.

Asymmetric mannich-type addition of ketene silyl acetals and thioacetals to N,N-dialkylhydrazones

The choice of the 2,6-diphenylpiperidine moiety as the N,N-dialkylamino auxiliary in simple aliphatic dialkylhydrazones and the use of scandium triflate as the catalyst in aqueous media appear as the key strategies that enable the highly diastereoselective nucleophilic addition of ketene silyl acetals and thioacetals. The reaction proceeds to afford the expected adducts in high yields (88-98%) and diastereomeric ratios of up to 99:1. N-N bond cleavage of adducts affords enantiomerically pure β-amino esters.