Pál Kolonits

Optically active 1-(benzofuran-2-yl)ethanols and ethane-1,2-diols by enantiotopic selective bioreductions

Abstract Enantiotopic selective reduction of 1-(benzofuran-2-yl)ethanones 1a – d , 1-(benzofuran-2-yl)-2-hydroxyethanones 4a – c and 2-acetoxy-1-(benzofuran-2-yl)ethanones 3a – c was performed by bakers yeast for preparation of optically active (benzofuran-2-yl)carbinols [( S )- 5a – d , ( S )- 6a – c and ( R )- 6a – c , enantiomeric excess from 55 to 93% ee].

Convenient synthetic route to (+)-faranal and (+)-13-norfaranal : The trail pheromone of pharaoh's ant and its congener 1

Abstract (+)-Faranal 1a , the trail pheromone of Pharaohs ant, and its congener, (+)-13-norfaranal 1b were synthetized from chiral building block 4 employing diastereoselective carbon-carbon bond formation. The application of crude pig liver esterase enzyme for the preparation of 4 is also discussed.

Synthesis and rearrangement of 13-thiaprostanoids

Abstract Thiaprostanoids 13 were prepared by conjugate addition of mercaptane 6 to cyclopentenones 12 and 20. Novel rearrangements of these compounds to 14 and 15 were interpreted as enolate induced [1,5]-sigmatropic shift on the corresponding dehydration products 16. Preparation of the various substrates and structural elucidation of new products are described.

A convenient synthetic route to (+)-faranal; The trail pheromone of pharaoh's ant

Abstract (+)-Faranal 1 , the trail pheromone of Pharaohs ant, was synthesized in 10 % overall yield starting from an easily available chiral building block 2 and employing diastereoselective carbon—carbon bond formation.

Synthesis of optically active 3-substituted-10-alkyl-10H-phenothiazine-5-oxides by enantioselective biotransformations

Abstract A series of racemic 10-alkyl-3-formyl-10 H -phenothiazine-5-oxides (±)- 2a – h were subjected to biotransformation with bakers yeast resulting in optically active aldehydes (+)- 2a – h and alcohols (−)- 3a – h in moderate enantiomeric excess. The racemic 10-alkyl-3-hydroxymethyl-10 H -phenothiazine-5-oxides (±)- 3a – h and 3-acetoxymethyl-10-alkyl-10 H -phenothiazine-5-oxides (±)- 4a – h obtained from the racemic aldehydes (±)- 2a – h were also tested in enantioselective lipase-catalyzed acetylations and alcoholysis reactions. The highest enantiomeric purities were achieved by a Novozyme 435-catalyzed acetylation–ethanolysis sequence, leading to optically active alcohols (−)- 3a – h in 83–92% e.e. A novel NMR method using enantiopure dibenzoyl tartaric acid as chiral additive was developed for determination of the enantiomeric composition of the optically active products.

Baker's yeast mediated preparation of (10-alkyl-10H-phenothiazin-3-yl)methanols

Abstract A series of 10-alkyl-10H-phenothiazine-3-carbaldehydes (2a–h) were obtained by Vilsmeier–Haack formylation from the corresponding 10-alkyl-10H-phenothiazines (1a–h) and reduced to (10-alkyl-10H-phenothiazine-3-yl)methanols (3a–h) by two alternative methods. The baker’s yeast catalyzed reaction proved to be superior over the NaBH4 reduction and yielded the desired 3-hydroxymethylphenothiazines (3a–h) almost quantitatively.

Studies on stereoselective approaches to β-carboline derivatives

Transformation of β-carboline derivatives into optically active entities were studied and the de and ee values of the resulted compounds were detected.

Synthesis of vinca alkaloids and related compounds. Part LXVIII. Two diastereoisomeric a spidosperma-eburnea type bis-indoles: Their synthesis and structure revisited

Abstract With the aim of clarifying their previously incorrectly depicted structure, the indole-indoline type compounds 11 and 12 were synthesized via different routes. The results presented here are a detailed account of the synthetic aspects of this work, and also redress some points of an earlier paper on this topic.

Synthesis of some pterocarpenes obtained from Brya ebenus

The syntheses of bryacarpenes-1, -2, and -4, [4,10-dihydroxy-3,8,9-trimethoxy-(1), 10-hydroxy-3,8,9-trimethoxy-(2), and 4-hydroxy-3,9,10-trimethoxy-6H-benzofuro[3,2-c][1]benzopyran (3)], (±)-bryaflavan [(±)-3′,6,7-trihydroxy-2′,4′-dimethoxyisoflavan (33)], 4-hydroxy-3,7-dimethoxy-(18) and 3,7-dimethoxy-6H-benzofuro[3,2-c][1]benzopyran-9,10-quinone (19) is described. The quinones are not identical with bryaquinone and deoxybryaquinone, for which structures (18) and (19) had been proposed previously. In the syntheses of the pterocarpenes the novel reduction of isoflavones to isoflavan-4-ones by di-isobutylaluminium hydride was used.

Synthesis of 4-aminopyrimidines from 1,2,4-oxadiazoles. Part 4. A novel heterocyclic rearrangement: formation of 4-hydroximinohexahydropyrimidines from 3-(2-aminoethyl)-4,5-dihydro-1,2,4-oxadiazoles

The 4,5-dihydro derivatives of 3-(2-aminoethyl)-5-substituted-1,2,4-oxadiazoles 1 have been prepared. These derivatives 8a–d rearrange readily, but in contrast to compounds 1, not to pyrazoles, but to 2-aryl-1-benzyl-4-hydroximinohexahydropyrimidines 9a–d. Studies on the mechanism of the 1→2 azole–azole, and the novel 8→9 azole–azine, rearrangements revealed that the site of the side chain nitrogen attack is controlled by the presence or absence of a delocalized π-electron system in the starting azole ring. Compound 9a and benzaldehyde gave cis- and trans-6-benzyl-3,5-diphenyl-5,6,7,8-tetrahydro-3H-[1,2,4]-oxadiazolo[4,3-c]pyrimidines 16 and 17, respectively. The structures of 9a, 16 and 17 were confirmed by X-ray crystallography.