Áron Szöllősy

Enantiomerically pure chiral pyridino-crown ethers: Synthesis and enantioselectivity toward the enantiomers of α-(1-naphthyl)ethylammonium perchlorate

Abstract Seven new enantiomerically pure chiral pyridino-crown ethers ( S,S )- 4 –( R,R )- 10 were prepared. Three of them [( S,S )- 4 , ( S,S )- 7 and ( R,R )- 10 ] contain one, and two of them [( S,S )- 5 and ( S,S )- 8 ] contain two linker chains with a terminal double bond. These linker chains were connected to the carbon atom at position 9 (opposite the pyridine moiety) of the macrocycle. The terminal double bond of the linker makes it possible to attach these ligands to silica gel to obtain chiral stationary phases (CSPs). The enantioselectivity of the new ligands toward the enantiomers of α-(1-naphthyl)ethylammonium perchlorate (NEA) was also determined by a titration 1 H NMR method.

Enantioselective hydrogenation catalyzed by highly active rhodium complexes of chiral phosphites with atropisomeric moieties

Abstract Excellent ees and extremely high activities are obtained in the rhodium-catalyzed hydrogenation of dimethyl itaconate using simple and readily available H 8 -BINOL based monodentate phosphites. The hydrogenation proceeds efficiently even at a substrate concentration of 5.263 mol L −1 and at a substrate to catalyst ratio (S/C) of 40,000 to give the product in 95.1% yield with up to 96.9% ee.

Synthesis of Bis(phosphonatomethyl)-, Bis(phosphinatomethyl)-, and Bis(phosphinoxidomethyl)amines, as Well as Related Ring Bis(phosphine) Platinum Complexes

Abstract The double Kabachnik–Fields condensation of primary amines with 2 equivalents of the other reagents (formaldehyde and a >P(O)H species, such as dialkyl phosphites, diphenylphosphine oxide, as well as the related dioxaphosphorine and oxaphosphorine derivatives) carried out under microwave conditions afforded the title products in 79–94% yields. The bis(phosphinoxidomethyl)amines were converted, after double deoxygenation, to the corresponding ring platinum complexes.

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.

A direct approach to selective sulfonation of triarylphosphines

Abstract A practical and convenient synthesis of mono-, di- and a trisulfonated phosphines from triphenylphosphine analogs, (2,4-dimethylphenyl) 3− n -(phenyl) n -phosphine and (4-methoxyphenyl) 3− n -(phenyl) n -phosphine ( n =0–2), is described, respectively. This represents an easy way to prepare water-soluble phosphines with complete selectivity, and with essentially no phosphine oxide formation.

One-pot synthesis of a novel C1-symmetric diphosphine from 1,3-cyclic sulfate. Asymmetric hydroformylation of styrene

Abstract Preparation of a novel homochiral diphosphine with C 1 -symmetry from the cyclic sulfate of (2 R ,4 R )-2,4-pentanediol is reported. Reaction of a lithium phosphide salt with the cyclic sulfate affords a γ-phospholylsulfate which can be converted to a diphosphine ligand on treatment with a second equivalent of lithium phosphide. Using this ligand in the platinum-catalyzed asymmetric hydroformylation of styrene, outstanding levels of regio- and enantiocontrol were obtained (89/11 iso / n isomeric ratio and 89% e.e.). The results are compared with those obtained with the analogous ligands (bdpp and bdbpp) having C 2 -symmetry. The novel unsymmetric ligand possessed the advantageous catalytic features of the C 2 -symmetric parent ligands.

Synthesis of phosphine-borane complexes of P-heterocycles

Abstract Dihydro-1H-phosphole-boranes 5 and 10 were prepared from phosphine oxides 1 and 9 respectively. Reaction of borane 5 with dichlorocarbene gave dihydrophosphole-dichloromethylborane 6 and tetrahydro derivative 7a as the main products, and dichlorocyclopropane 8 as the minor component. Dichlorocarbene addition reaction of boranes 10 did not afford the corresponding phosphabicyclohexanes, but the dichloromethylborane complexes of the dihydro- and tetrahydrophospholes (11 and 7 respectively). Phosphabicyclohexaneborane 13 was synthesized from P-oxide 12 by change in the functionality. The dihydrophosphinine-boranes (16) were prepared by cyclopropane ring opening of phosphabicyclohexane 13, or by change in the functionality of P-oxide 15. Reaction of dihydrophosphinine-boranes 17 with dichlorocarbene gave traces of dihydrophosphinine-dichloromethylborane 18 instead of the phosphepine. The phosphepine-borane (20) was synthesised from oxide 19. The preparation of unsaturated phosphine-boranes was complicated by reduction side-reactions. The products were characterized by 31P, 11B, 1H and 13C NMR, as well as MS data.

Synthesis and stereochemistry of spiropyrazolines

Spiropyrazolines have been synthesized by 1,3-dipolar cycloaddition of an 2-arylidene-1-tetralone, 3-arylidene-chromanones, -1-thiochromanones, and -flavanones with diazomethane. The relative configuration and stereochemistry of the products have been determined by means of one-dimensional difference N.O.E. measurements. It is shown that ring-closure reaction is regioselective, yielding stereohomogeneous spiropyrazolines in one step.

A simple method for the preparation of various 1-oxo-hydrindene-2-acetic and -propionic acids. Valuable precursors of strigol and its analogues

Abstract An improved annulation sequence is presented, making use of the one-pot cyclization of 5-nitropentan-2-one and cyclopent-2-enone diesters to afford 7-methyl-4-nitro-1-oxohydrindene derivatives. Functional group elaborations of these intermediates lead to a series of the title compounds, which could be readily converted to the tricyclic moieties of strigol and its analogues of biological importance.

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.