Milan Potáček

Novel thermal tetracyclization by intramolecular azine criss-cross addition

An easy, thermally initiated reaction of homoallenylazine 1 affords the new fused heterocyclic system 2 consisting of four five-membered rings in ten-membered carbocycle around the hydrazine moiety.

New fused heterocycles by combined intra-intermolecular criss-cross cycloaddition of nonsymmetrical azines ☆

Thermally induced intra-intermolecular criss-cross cycloaddition of nonsymmetrical azines in the presence of phenyl isocyanate is described. This one-pot reaction gives heterocyclic compounds containing three fused five-membered rings. The molecular and crystal structure of the products is reported and discussed.

SANGUINARINE PSEUDOBASE: RE-EXAMINATION OF NMR ASSIGNMENTS USING GRADIENT-ENHANCED SPECTROSCOPY

The formation of sanguinarine pseudobase (6‐hydroxydihydrosanguinarine) was studied by 1D and 2D NMR spectroscopy. The unequivocal evidence of a hemiaminal OH group and unambiguous 1H, 13C and 15N NMR assignments of this compound are discussed.

Microwave-Assisted Synthesis of Substituted Hexahydro-pyrrolo[3,2-c]quinolines

New compounds with the ethyl hexahydro-1H-pyrrolo[3,2-c]quinoline-2-carboxylate skeleton were prepared by microwave-assisted intramolecular 1,3-dipolar cycloaddition reactions. The reactions were carried out under solvent-free conditions and compared with the same reaction in the presence of a solvent and a catalyst. Steric effects on the selectivity of the reaction were noted and evaluated.

Diethyl Acetonedicarboxylate - a Precursor for the Synthesis of New Substituted 4-Aminoquinolines and Fused 4-Aminopyridines*

SummaryThe reaction of cyclic enaminonitriles1 with diethyl acetonedicarboxylate (2) affords fused 4-amino-3-ethoxycarbonyl-2-ethoxycarbonylmethyl-pyridines4. The course of the reaction and the yield of cyclic products were promoted by tin(IV)chloride. N-substituted diethyl 3-aminoglutaconates3 seem to be intermediates of the cyclization reaction.ZusammenfassungDie Reaktion der cyclischen Enaminonitrile1 mit Diethylacetondicarboxylat (2) ergibt kondensierte 4-Amino-3-ethoxycarbonyl-2-ethoxycarbonylmethyl-pyridine4. Der Reaktionsablauf und die Ausbeute werden durch Zusatz von Zinn(IV)chlorid gefördert. Wahrscheinlich verläuft die Reaktion über N-substituierte Diethyl-3-amino-glutaconate3 als Zwischenprodukte.

A solvent-free method for substituted imidazolidin- 4-ones synthesis

A new method of the solvent-free synthesis of substituted imidazolidin-4-ones is described. The method is developed for microwave-assisted solvent-free conditions and compared with classical thermally initiated solvent-free conditions. In both cases the reaction proceeds with good yields. However, the reaction under microwave conditions is accelerated six-times. Thermal effect of the microwaves is observed.

Criss-cross Cycloadditions on Ketazines Derived from Alicyclic Ketones

The reactivity of alicyclic ketazines in criss-cross cycloadditions was investigated. They react with potassium cyanate and ammonium thiocyanate in the presence of acetic acid to form spirocyclic perhydro[1,2,4]triazolo[1,2-alpha][1,2,4]triazole-1,5-diones and perhydro[1,2,4]triazolo[1,2-alpha][1,2,4]triazole-1,5-dithiones, respectively, in relatively high yields.

Molecular and Crystal Structures of Three Berberine Derivatives

Berberine azide, berberine thiocyanate, and 8-cyano-8H-berberine were prepared from berberine chloride, a quaternary protoberberine alkaloid. The molecular and crystal structures of all compounds are reported and discussed.

Substituted Diazatetracyclo[4.4.0.13,10.15,8]dodecanes as Stable Caged Proton Sponges

Herein, we report a molecular framework design differing significantly from the traditional topology of proton sponges. We developed a synthetic approach to the preparation of caged secondary amines by acid-catalyzed rearrangement of fused tetracyclic heterocycles synthesized by intramolecular criss-cross cycloaddition. Alkylation of amines led to air nonsensitive diazatetracyclo[4.4.0.1(3,10).1(5,8)]dodecanes (DTDs) with rare alicyclic scaffolding in high overall yields. Their pK(BH)+ values were determined by transprotonation experiments as well as their sensitivity toward nucleophiles, acids and bases. Crystal structures of free base and monoprotonated form are discussed.

A new route to 1,4-disubstituted 5-thioxoperhydroimidazo[4,5-d]imidazol-2-ones

1,4-Disubstituted 5-thioxoperhydroimidazo[4,5-d]imidazol-2-ones were prepared by one-pot criss-cross cycloaddition reactions of 1,4-disubstituted 1,4-diazabuta-1,3-dienes with HNCS and HNCO generated in situ from potassium salts by acetic acid.