István Kádas

trans-3-Aryl-4-nitro-pyrrolidines via 1,3-dipolar cycloaddition of nonstabilized azomethine ylide to ß-nitro styrenes

Abstract Various β-nitro styrenes undergo 1,3 dipolar cycloaddition with the azomethine ylide derived from sarcosine and paraformaldehyde to give 3-aryl-4-nitro-pyrrolidines in good yield.

Influence of Ag(I) and Li(I) Catalysts for 1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides. Reversal of the Stereochemistry

Abstract The 1,3-dipolar cycloadditions of ester stabilised azomethin ylides to aryl-nitro olefines catalysed by Li(I) gave products of different stereoselectivity than those arising from processes catalysed by Ag (I). The cycloadditions involve the stereospecific generation of dipoles. The formation of products with reverse stereochemistry when using different metal salt catalysts is caused by the differences in endo and exo approaches of nitro-ethylene compounds.

Inverse-electron-demand Diels–Alder reactions of 4-aryl-2-pyrones with electron-rich dienophiles

Abstract The Diels–Alder reaction of 4-aryl-pyrones with electron-rich dienophiles afforded substituted biaryl derivatives in most cases. At the minimal temperatures necessary for a measurable conversion of the starting pyrones, the bicyclic lactones, the primary products of the condensation, underwent cycloreversion by extruding carbon dioxide and then aromatised through further eliminations. In the case of the more active 4-aryl-6-chloro-pyrone, a formal substitution was observed instead of the expected cycloaddition with an active dienophile, while in its reaction with a Schiff-base the primary product of the cycloaddition was trapped through the formation of a new tetrahydropyridine derivative.

1,3-dipolar cycloaddition approach towards the stereoselective preparation of aza-cephalotaxine skeleton

Abstract The aza-analogue of cephalotaxine skeleton has been prepared by series of reactions which include a 1,3-dipolar cycloaddition in 100% diastereoselectivity.

Highly enantioselective organocatalytic conjugate addition of nitromethane to benzylidene acetones

Six active 4-aryl-5-nitro-pentan-2-ones were synthesized enantioselectively from the corresponding 5-aryl-butenones by asymmetric Michael addition of nitromethane using an imidazolidine-type enantioselective organocatalyst. The ee ratio of the products were between 67 and 100%, determined by HPLC with Chiracel OD. Molecular and crystal structure of 3,4-methylenedioxy-phenyl-5-nitro-pentan-2-one has been studied by single crystal X-ray diffraction.

1,3-dipolar cycloaddition approach towards the stereoselective preparation of Aza-cephalotaxine skeleton

Abstract The aza-analogue of cephalotaxine skeleton has been prepared by series of reactions which include a 1,3-dipolar cycloaddition in 100% diastereoselectivity.

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.

Direct and indirect radical denitrations of intermediates in the synthesis of sorgolactone and its nuclear analogs

Abstract Denitration of various important intermediates in the synthesis of sorgolactone and its analogs using radical chemistry on nitroketones or on the derived isocyanides is described. The nitro group is needed for the first step of the annellation process, the Michael addition of substituted nitroalkanes to cyclopentenones. Then it can be removed directly or after reduction to the amine or via the ketone obtained by the Nef-reaction.

1,3-dipolar cycloaddition of 3,4-dihydro-6,7-dimethoxyisoquinoline-N- methoxycarbonyl methylide with Schiff bases

Abstract 1,3-Dipolar cycloaddition of 3,4-dihydro-6,7-dimethoxyisoquinoline- N -methoxycarbonyl methylide to Schiff bases results in the imidazo[2,1- a ]isoquinolines as single racemates. The cycloadducts obtained are exo isomers, with one exception. The only compound with endo structure isomerized via cycloreversion followed by cycloaddition to the thermodynamically stable exo isomer. Structural assignment of the products was achieved by comprehensive two-dimensional NMR methods. Both the exo and endo isomers exist in a trans cis-1 cis-2 conformational equilibrium.

Syntheses of the terpenoid precursors cyclopent-2-enone and cyclohex-2-enone diesters

SummaryTwo reaction pathways were elaborated for the practical and convenient synthesis of the title compounds. The first route applies a bromination-dehydrobromination sequence to introduce the double bond into 1-alkoxycarbonyl-2-oxocycloalkylacetic and propionic esters (4a–c,7a,b). The application of 2,6-lutidine for dehydrobromination of α-bromocycloalkanones diesters (5a–c,8a,b) provides sufficient selectivity to carry out this step without affecting the sensitive ester group. Alternative pathways, involvingMichael reaction of diethyl 2-acetylsuccinate or -glutarate with acrolein and subsequent intramolecular aldol condensation, are presented in the case of cyclohex-2-enone derivatives2a,b.ZusammenfassungFür praktische und bequeme Synthesen der Titelverbindungen werden zwei Reaktionswege präsentiert. Der erste Weg basiert auf einer Bromierungs-Dehydrobromierungs-Sequenz zur Einführung der Doppelbindung in die 1-Alkoxykarbonyl-2-oxocycloalkylessig- und-propionsäureester (4a–c,7a,b). Die Anwendung von 2,6-Lutidin zur Dehydrobromierung der α-Bromocycloalkanone-diester (5a–c,8a,b) sichert die ausreichende Selektivität, ohne die empfindlichen Estergruppen anzugreifen. Im Falle der Cyclohex-2-enon-Derivate (2a,b) zeigen wir einen alternativen Weg, der auf derMichael-Reaktion von Diethyl-2-acetyl-succinat bzw. -glutarat mit Acrolein basiert; die anschließende intramolekulare Aldol-Kondensation liefert die Zielprodukte.