Enantioselective 1,3-Dipolar Cycloaddition Using (Z)-α-Amidonitroalkenes as a Key Step to the Access to Chiral cis-3,4-Diaminopyrrolidines.

The enantioselective 1,3-dipolar cycloaddition between imino esters and (Z)-nitroalkenes bearing a masked amino group in the ß-position was studied using several chiral ligands and silver salts. The optimized reaction conditions were directly applied to the study of the scope of the reaction. The determination of the absolute configuration was evaluated using NMR experiments and electronic circular dichroism (ECD). The reduction and hydrolysis of both groups was performed to generate in an excellent enantiomeric ratio the corresponding cis-2,3-diaminoprolinate.

Switching Diastereoselectivity in Catalytic Enantioselective (3+2) Cycloadditions of Azomethine Ylides Promoted by Metal Salts and Privileged Segphos-Derived Ligands.

Catalytic enantioselective 1,3-dipolar cycloaddition between imino esters and electrophilic alkenes, employing chiral metal complexes derived from copper(I) and silver(I) salts and (S)-DM- or (S)-DTBM-Segphos as ligands produces diastereodivergently exo- or endo-cycloadducts, respectively. The effect of the functional group of the dipolarophile and the fine tuning of the catalyst plays an important role in promoting reverse diastereoselectivities. The origins of experimentally observed enantioselectivity and diastereoselectivity data, as well as the origin of the observed switched endo/exo ratios, are also explained by means of density functional theory calculations.

Multilayer graphene functionalized through thermal 1,3-dipolar cycloadditions with imino esters: a versatile platform for supported ligands in catalysis.

Multilayer graphene (MLG), obtained by mild sonication of graphite in NMP or pyridine, was fully characterized via atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoemission spectroscopy (XPS). Then, it was functionalized via 1,3-dipolar cycloaddition with azomethine ylides generated by thermal 1,2-prototropy of various imino esters. The resulting MLG, containing substituted proline-based amine functions, was characterized by XPS and it showed high nitrogen loading, ranging from 0.6 to 4.2 at% depending on the imino ester used. Among these functionalized MLGs a probe sample was subjected to ester hydrolysis and used as a heterogeneous N,O-chelating ligand to coordinate iridium atomic centers. This supported complex was also characterized by XPS and its catalytic activity was tested in the hydrogen transfer reduction of acetophenone, obtaining up to 85% yield. Furthermore, this catalyst could be recycled up to four times.