Expeditive synthesis of glycodendrimer scaffolds based on versatile TRIS and mannoside derivatives

A new family of glycodendrimer scaffolds containing 12 and 18 peripheral alpha-d-mannopyranosidic units has been synthesized by Cu(I)-catalyzed [1,3]-dipolar cycloadditions using sulfurated dendritic scaffolds bearing alkyne functionalities and novel TRIS derivatives.     

Nucleophilic addition of phenol derivatives to methyl 1-nitrocyclopropanecarboxylates

Nucleophilic ring opening of methyl 1-nitrocyclopropanecarboxylates by phenol derivatives in the presence of Cs2CO3 is described. The reaction tolerates a variety of substituents on both the aromatic alcohol and the cyclopropane and affords the products in good yields (53-84%) and with complete preservation of the enantiomeric excess at C-4. The methodology was applied in an enantioselective synthesis of the norepinephrine reuptake inhibitor atomoxetine (Strattera).     

Total synthesis of (+)-lepadin B: stereoselective synthesis of nonracemic polysubstituted hydroquinolines using an RC-ROM process

This communication describes a new tandem metathesis reaction for which an RC-ROM mechanism was experimentally supported. This process was successfully applied to the synthesis of cis-fused polyhydroquinolines enabling a short stereoselective total synthesis of ent-lepadin B.     

General method for the expedient synthesis of salt-free diorganozinc reagents using zinc methoxide

The effect of counterions has a great impact on the solubility of magnesium salts in Et2O. By reacting Zn(OMe)2 with readily available Grignard reagents, it was possible to induce the complete precipitation of magnesium salts and then obtain salt-free diorganozinc reagents after centrifugation/filtration. This practical method to generate dialkylzinc reagents as well as mixed diorganozinc reagents was successfully tested in various catalytic enantioselective reactions, proving the purity of the product and its synthetic usefulness.     

Highly chemoselective metal-free reduction of tertiary amides

This communication describes the chemoselective metal-free reduction of tertiary amides to the corresponding amines. Hantzsch ester is used as a mild reducing agent for the reduction of trifluoromethanesulfonic anhydride activated amides providing the tertiary amines with high functional group tolerance.     

Coordination "oligomers" in self-assembly reactions of some "tritopic" picolinic dihydrazone ligands-mononuclear, dinuclear, hexanuclear, heptanuclear, and nonanuclear examples

"Tritopic" picolinic dihydrazone ligands with tridentate coordination pockets are designed to produce homoleptic [3 x 3] nonanuclear square grid complexes on reaction with transition-metal salts, and many structurally documented examples have been obtained with Mn(II), Cu(II), and Zn(II) ions. However, other oligomeric complexes with smaller nuclearities have also been discovered and identified structurally in some reactions involving Fe(II), Co(II), Ni(II), and Cu(II), with certain tritopic ligands. This illustrates the dynamic nature of the metal-ligand interaction and the conformationally flexible nature of the ligands and points to the possible involvement of some of these species as intermediates in the [3 x 3] grid formation process. Examples of mononuclear, dinuclear, hexanuclear, heptanuclear, and nonanuclear species involving Fe(II), Co(II), Ni(II), and Cu(II) salts with a series of potentially heptadentate picolinic dihydrazone ligands with pyrazine, pyrimidine, and pyridine end groups are described in the present study. Iron and cobalt complexation reactions are complicated by redox processes, which lead to mixed-oxidation-state Co(II)/Co(III) systems when starting with Co(II) salts, and reduction of Fe(III) to Fe(II) when starting with Fe(III). Magnetic exchange within the polynuclear structural frameworks is discussed and related to the structural features.     

Removal, recovery, and recycling of triarylphosphonium-supported tin reagents for various organic transformations

Phosphonium-supported tin reagents and catalysts were prepared and were shown to be effective in Stille couplings, radical dehalogenations, radical cyclizations, and carbonyl allylations. Not only could the tin residues be removed from the crude reaction mixture through a phase separation process but also they could be recovered and recycled.     

Characterization of titanium dioxide nanoparticles dispersed in organic ligand solutions by using a diffusion-ordered spectroscopy-based strategy

Diffusion-ordered NMR spectroscopy (DOSY NMR) is presented as a tool for the determination of the diffusion coefficients of organic ligands in suspensions of titanium dioxide nanoparticles. The nanoparticles were prepared by a sol-gel process by hydrolysis and condensation reactions of titanium tetra-n-butoxide in the presence of pentane-2,4-dione (acacH: acetylacetone), as well as para-toluenesulfonic acid (pTsA) and n-butanol (nBuOH). NMR spectroscopic studies were performed in various deuterated solvents, on both dispersed xerosols and diluted sols. The bipolar-pulsed field gradient longitudinal eddy-current delay (LED) pulse sequence was used for data acquisition. The data were processed by inverse Laplace transformation (ILT), by using a maximum entropy algorithm, to afford 2D DOSY spectra. Different diffusion regimes for organic ligands in the bound and unbound states were successfully discriminated, more particularly in [D3]acetonitrile, thus allowing assessment of their interactions with the nanoparticles.     

Stereoselective synthesis of 13Z retinoic acids via β-methylenealdehydes as synthons

A stereoselective synthesis of 13Z retinoic acids via β-methylenealdehydes is described. In methylene-de-oxo-bisubstitution reactions (Knoevenagel, Stobbe, etc.), these new synthons produce stereoselectively E olefins. Hence, a synthesis of 13Z retinoic acids is described, via a stereospecific monodecarboxylation of carboxy-14-retinoic acids.