Tamás Holczbauer

Double Diastereocontrol in Bifunctional Thiourea Organocatalysis: Iterative Michael–Michael–Henry Sequence Regulated by the Configuration of Chiral Catalysts

The importance and reactivity consequences of the double diastereocontrol in noncovalent bifunctional organocatalysis were studied. The results suggest that the bifunctional thioureas can have synthetic limitations in multicomponent domino or autotandem catalysis. Nevertheless, we provided a means to exploit this behavior and used the configuration of the chiral catalyst as a control element in organo-sequential reactions.

Annular desmotropy of three pairs of seven-membered heterocycles confirmed by X-ray crystallography

The tautomers of 3-ethoxycarbonyl-2-phenyl-4,1-benzothiazepine and its 2-(4-methylphenyl) and 2-(4-chlorophenyl) derivatives, identified in solution by spectroscopic means, could be separated in the form of single-crystals suitable for X-ray diffraction. This is at present a unique situation in the literature on desmotropy. For the three desmotropic pairs, the bond lengths and angles present in the puckered seven-membered rings are fairly consistent within each group of desmotropes, but differ between the imines and the enamines. The structural similarity within the imines is revealed best by the isostructurality of the methyl and chloro derivatives, while the puckering differences between the heterorings of the desmotropic groups are reminiscent of conformational polymorphism.

Expedient and Diastereodivergent Assembly of Terpenoid Decalin Subunits having Quaternary Stereocenters through Organocatalytic Robinson Annulation of Nazarov Reagent

We report an expedient approach to highly functionalized cis- and trans-decalines that could function as key structural subunits toward the synthesis of various classes of terpenoids. Key to the strategy is an organocatalyzed Robinson annulation reaction of the Nazarov reagent that affords chiral enone building blocks with high enantioselectivities. The quaternary carbon stereogenic center can direct the subsequent reactions and allow the rapid and diastereoconvergent assembly of complex decalines with contiguous stereocenters.

Mechanistic investigations of a bifunctional squaramide organocatalyst in asymmetric Michael reaction and observation of stereoselective retro-Michael reaction

The mechanism of the addition of acetylacetone to β-nitrostyrene catalyzed by a cinchona based squaramide catalyst was studied in detail under synthetically relevant conditions. The reaction was monitored by in situ IR and 1H-NMR spectroscopy and a reaction mechanism was proposed based on these kinetics experiments. It was found that the reaction shows nearly first order dependence on both substrates and catalyst. Our investigations also revealed that the catalyst was able to promote stereoselective retro-Michael reaction.

New Atropisomeric Amino Alcohol Ligands for Enantioselective Addition of Diethylzinc to Aldehydes

Efficient synthesis of several new atropisomeric amino alcohols having 1-phenyl-1H-pyrrole skeleton are reported. Steric arrangements of the products were confirmed by a single-crystal X-ray measurement. The consequences of the size of the N-substituents on enantioinduction were examined by employing the enantioselective catalytic addition of diethylzinc to a series of substituted benzaldehydes (yields 91-97%, up to 85% enantiomeric excess). The special effect of the ortho methoxy group of the substrate on the enantioinduction is also interpreted.

Ring Transformation of Unsaturated N-Bridgehead Fused Pyrimidin-4(3H)-ones: Role of Repulsive Electrostatic Nonbonded Interaction

Thermal ring transformation ability of unsaturated N-bridgehead fused pyrimidin-4(3H)-ones A is governed by both the steric and the electrostatic interactions between the oxygen of the carbonyl group and the substituent in the peri position.

Dichloridobis(2-methoxy­dibenzo[c,e][1,2]oxaphospho­rine-κP)platinum(II) trichloro­methane solvate

The title compound, [PtCl2(C13H11O2P)2]·CHCl3, has a rare PtCl2 bridging of two dibenzooxaphosphorine ligands through the metal atom. The PtII ion is in a slightly distorted square-planar environment. The trichloromethane solvent molecule shows rotational disorder (major occupancy is 0.75) and is placed near to the inversion centre at (1/2, 1/2, 0) in channels parallel to the a axis. The solvent molecule is linked to the complex molecule via intermolecular bifurcated C—H⋯Cl and C—H⋯O hydrogen bonds. The crystal structure is further stabilized by π–π interactions involving the benzene rings, with a centroid–centroid distance of 3.658 (8) Å.

Enzyme-catalyzed kinetic resolution of N-Boc-trans-3-hydroxy-4-phenylpyrrolidine

AbstractThe first enzyme-catalyzed kinetic resolution of tert-butyl-3-hydroxy-4-phenylpyrrolidine-1-carboxylate is presented. Enzyme, solvent and temperature optimization resulted in a new resolution method with E = 40 enantioselectivity. The acetate derivative of the (+)-(3S,4R) enantiomer formed while the (−)-(3R,4S) isomer remained intact. Very good enantioselectivities (E > 200) were achieved in the enzyme-catalyzed alcoholysis of the racemic acetate in i-propanol and t-butanol where the (+)-(3S,4R) enantiomer was prepared in pure form (ee > 99.7%). Absolute configuration of the (−)-(3R,4S)-enantiomer was determined by single crystal X-ray diffraction method.

Synthesis of novel 17-(5’-iodo)triazolyl-3-methoxyestrane epimers via Cu(I)-catalyzed azide-alkyne cycloadditon, and an evaluation of their cytotoxic activity in vitro

The regioselective Cu(I)-catalyzed 1,3-dipolar cycloaddition of 3-methoxyestrane 17α- and 17β-azide epimers (3 and 5) with different terminal alkynes afforded novel 1,4-substituted triazolyl derivatives (8a-f and 11a-f). If the Ph3P in the classical CuAAC process was replaced by Et3N, the formation of small quantities of 5-iodotriazoles (9a-f and 11a-f) was observed. For the preparation of 5-iodo-1,2,3-triazoles (9a-f and 11a-f), an improved method was developed, directly from steroidal azides and terminal alkynes, in reactions mediated by CuI and ICl as iodinating agents. The antiproliferative activities of the structurally related triazoles were determined in vitro with the microculture tetrazolium assay on six malignant human cell lines of gynecological origin (HeLa, A2780, MCF7, MDA-MB-231, MDA-MB-361 and T47D). X-ray analysis revealed the presence of the iodo substituent on the 1,2,3-triazole ring.

Crystal structure of di­aqua­tris­(1-ethyl-1H-imidazole-κN3)(sulfato-κO)nickel(II)

The NiII ion atom is octahedrally coordinated in diaquatris(1-ethyl-1H-imidazole)sulfatonickel(II). There are three organic ligands, two water and the sulfate anion coordinated around the NiII centre. Two complex molecules form an inversion dimer via two pairs of O—H⋯O hydrogen bonds between the coordinating sulfate anion and a water molecule in the unit cell.