Szabolcs Balogh

Asymmetric hydrogenation of C=C double bonds using Rh-complex under homogeneous, heterogeneous and continuous mode conditions

A green process for enantioselective hydrogenation of dehydroamino acid derivatives and dimethyl itaconate with a rhodium catalyst modified by a new phosphine–phosphoramidite has been developed providing 97.7–99.8% enantioselectivity in green solvents such as ethylene carbonate and propylene carbonate. The L-DOPA precursor was obtained by simple filtration in 71% yield with 99.5% ee. Dimethyl itaconate was hydrogenated under solvent-free condition at 50 °C with 98.7% ee. The new rhodium complex was heterogenized on a mesoporous Al2O3 support using phosphotungstic acid (PTA) as an anchoring agent and tested in heterogeneous batch and flow reaction modes. The supported catalyst was reused eight times in the batch mode with over 97% ee and used over 12 hours in the flow reaction mode with an average of 97% ee in the asymmetric hydrogenation reaction of (Z)-α-acetamidocinnamic acid methyl ester.

Phosphine–phosphite ligands: chelate ring size vs. activity and enantioselectivity relationships in asymmetric hydrogenation

A series of new phosphine-phosphite ligands P(C)(n)OP (n = 1-4) have been synthesized and used for rhodium-catalyzed asymmetric hydrogenation of prochiral olefins in order to study the effect of the chelate ring size. Excellent ees (up to 97.5%) were obtained in the hydrogenation of dimethyl itaconate and an increase of activity and enantioselectivity was observed in the hydrogenation of (Z)-α-acetamidocinnamic acid methyl ester with the increasing length of the backbone of the ligands.

Aminoalkyl-phosphine (P,N) ligands with pentane-2,4-diyl backbone in asymmetric allylic substitution reactions

The asymmetric allylic substitution reaction of rac-1,3-diaryl-2-propenyl acetates with several C- and N-nucleophiles catalyzed by the palladium-complexes of eleven structurally analogous aminoalkyl-phosphines (P,N) with pentane-2,4-diyl backbone is reported. The role of the N-substituents and the influence of the ligand/palladium molar ratio on the activity and enantioselectivity of the catalytic system are studied. The solvent and the temperature dependence of the catalytic reaction were also assessed yielding enantioselectivities up to 95% in alkylation and 90% in amination processes under optimized reaction conditions.Graphical abstract