László Hegedűs

Effect of carbon support properties on enantioselective hydrogenation of isophorone over palladium catalysts modified with (-)-dihydroapovincaminic acid ethyl ester

The support-effect was investigated in the enantioselective hydrogenation of isophorone over Pd catalysts prepared on different carbon supports. Carbon supports with different specific surface area and activated carbons with different surface chemistry were used. The Pd catalysts, obtained by different reduction methods of the catalyst precursor, had different dispersion. The low dispersion was advantageous for the high enantioselectivity and the different supports had influence on the ee due to their different specific surface area and surface chemistry.

Synthesis of the Spiro Derivatives of 1,2-Oxaphosphetes by [2+2] Cycloaddition of Cyclic 1-(2,4,6-Triisopropylphenyl)phosphine Oxides with Dimethyl Acetylenedicarboxylate†

Abstract Members of a new heterocyclic family, 1,2-oxaphosphetes were prepared by the unexpected [2+2] cycloaddition of the PO group of 1-(2,4,6-triisopropylphenyl) P-heterocycles with the acetylene moiety of dimethyl acetylenedicarboxylate. The new oxaphosphetes are spiro derivatives of the starting heterocycles and exhibit a phosphorus atom with trigonal bipyramidal geometry. PM3 semiempirical calculations justified the novel reaction path and suggested a stepwise reaction mechanism.

The first enantioselective synthesis of α-aminophosphinates

The first enantioselective synthesis of substituted α-aminophosphinic acids was carried out by the addition of ethyl phenylphosphinate to chiral imines in the absence of base or other catalyst.

Hydrogenation of pyrrole derivatives Part III. Hydrogenation of methyl 1-methyl-2-pyrroleacetate

Abstract A new hydrogenation method for the saturation of the pyrrole ring has been applied in the hydrogenation of methyl 1-methyl-2-pyrroleacetate in non-acidic medium. Various catalytic metals and solvents have been screened. High conversion and selectivity were achieved with rhodium and ruthenium catalysts. In palladium catalyzed hydrogenations the selectivity was improved by appropriate solvents.

Synthesis of ribo-hexopyranoside- and altrose-based azacrown ethers and their application in an asymmetric Michael addition

The synthesis of four new ribo-hexopyranoside-based chiral lariat ethers of monoaza-15-crown-5 type and two altropyranoside-based crown ethers were elaborated. Our syntheses utilized the regioselective ring opening of the oxiran moiety of the 2,3-anhydro sugars by nucleophilic reagents to afford the key intermediates. The reaction of methyl-2,3-anhydro-4,6-O-benzylidene-α-D-mannopyranoside with ethanolamine is especially of interest to afford a 3-substituted altropyranoside. One of the ribo-hexopyranoside-based lariat ethers with a 4-methoxyphenyl substituent induced an enantioselectivity of 80% when used as catalyst in the Michael addition of diethyl acetamidomalonate to trans-β-nitrostyrene under phase transfer catalytic conditions.

Selective hydrogenation of exocyclic α,β-unsaturated ketones:: Part I. Hydrogenations over palladium

Exocyclic α,β-unsaturated ketones were hydrogenated to the corresponding saturated ketones with Pd catalysts. The effect of solvents, basic and poisoning additives and various supports on conversion and selectivity was investigated. The conditions, under which the reaction afforded the saturated ketones with complete selectivity and appropriate reaction rate, were determined. The highest selectivities were obtained over Pd/C, in toluene, at atmospheric pressure and in the presence of pyridine.

The First Enantioselective Total Synthesis of (−)-trans-Dihydronarciclasine

A feasible and enantioselective total synthesis of (-)-trans-dihydronarciclasine [(-)-1], a highly biologically active alkaloid, was devised starting from vanillin (8). The key step of this new synthesis was an asymmetric, organocatalytic Michael addition, in which an optically active nitropentanone [(-)-13] was obtained from a butenone derivative (12). Excellent enantioselectivity (>99% ee) was achieved using the (8S,9S)-9-amino(9-deoxy)epiquinine (16) organocatalyst. The target molecule can be prepared in 13 steps from compound (-)-13. The total synthesis has provided a facile and first access to the ent-form of naturally occurring (+)-trans-dihydronarciclasine, a highly potent cytostatic alkaloid.

Stereoselective synthesis of trans-dihydronarciclasine derivatives containing a 1,4-benzodioxane moiety

Some new trans-dihydronarciclasine derivatives containing a 1,4-benzodioxane moiety were stereoselectively synthesised using our feasible and efficient method developed recently. These new phenanthridone alkaloid analogues were obtained in both racemic and optically active forms. High enantioselectivities (up to 99% ee) were achieved by applying (8S,9S)-9-amino(9-deoxy)epiquinine as an organocatalyst. Due to a side reaction, various methoxyphenanthridine regioisomers were also prepared which afforded further synthetic trans-dihydronarciclasine analogues modified in the ring A of the phenanthridone scaffold.Graphical abstract