Eszter Gács-Baitz

Structural characterization of the new polymorphic mesophases formed by bent-core molecules

A new achiral banana-shaped five-ring 2-methylresorcinol derivative fluorinated on the outer rings has been synthesized. This compound exhibits four antiferroelectric smectic phases characteristic for bent-core molecules (B2, B′2, B″2, B5). In addition, a highly viscous solid-like phase has been detected which also shows electro-optical switching. This is the first switchable highly ordered B phase. The characterization of the mesophases was made by X-ray diffraction, electro-optical measurements and dielectric spectroscopy.

Teucrins H1-H4, novel clerodane-type diterpenes from Teucrium hyrcanicum

Abstract The structure and stereochemistry of teucrins H1, H2, H3 and H4, four novel diterpenes from Teucrium hyrcanicum have been established by detailed studies of the PMR and 13 C NMR spectra, CD results and chemical transformations. Teucrin H4, a minor constituent is shown to possess a unique stereochemistry hitherto not reported for related diterpenoids.

Ester type banana-shaped liquid crystalline monomers: synthesis and physical properties

New ester-type banana (bent-shaped) monomers, 1,3-phenylene bis[4′-(alken-1-yloxy)-biphenyl-4-carboxylate]s Ia–Vb, with different substituent(s) on the central phenyl ring (H, CH3, Cl or NO2) and alkenyl tails in the side arms (decenyl or undecenyl) were prepared. The analogues IIIa–IVb with 4-chloro- or 4,6-dichloro-substituents exhibited a nematic phase, while Va,Vb with 2-nitro-substituent showed a B7 phase at relatively low temperature. All the compounds were stable, no degradation or polymerization was observed under applied electric fields or heat treatments. Electro-hydrodynamic instabilities were observed in the nematic phase of each sample. In the B7 phase of Vb there was an electro-optical switching in the range 112–114.5 °C with a switching time of about 150 µs at 20 V µm−1 field. At lower temperatures no electro-optical switching occurred, but a ferroelectric-type spontaneous polarization of 22 nC cm−2 could be detected. The bend angle was calculated by the semiempirical CAChe/MOPAC/PM5 method.

Synthesis of vinca alkaloids and related compounds XLVIII synthesis of (+)-catharanthine and (±)-allocatharanthine☆

Abstract The first synthesis of natural (+)-catharanthine (ulbar>1) has been achieved in a few steps and in ∼20 % overall yield based on indole-3--acetic acid. The isomeric (±)-allocatharanthine was also prepared.

An economic synthesis of 1,2,3,4-tetra-O-acetyl-5-thio-D-xylopyranose and its transformation into 4-substituted-phenyl 1,5-dithio-D- xylopyranosides possessing antithrombotic activity.

D-Xylose was converted via 1,2-O-isopropylidene-alpha-D-xylofuranose (4) into 3-O-benzoyl-5-S-benzoyl-1,2-O-isopropylidene-alpha-D-xylofuranose which, after methanolysis, acetylation and subsequent acetolysis afforded 1,2,3,4-tetra-O-acetyl-5-thio-alpha-D-xylopyranose (14) in an overall yield of 36%. Reaction of 4 with thionyl chloride gave a mixture of the diastereomeric cyclic sulfites, the structures of which were established by X-ray crystallography. Their oxidation with sodium periodate afforded the corresponding cyclic sulfate 23. Treatment of 23 with potassium thioacetate gave the potassium salt of 5-S-acetyl-1,2-O-isopropylidene-alpha-D-xylofuranose 3-O-sulfonic acid (26) which, after methanolysis, acetylation and subsequent acetolysis afforded 14 in an overall yield of 56%. Treatment of 4 with sulfuryl chloride gave a mixture containing 5-chloro-3-O-chlorosulfonyl-5-deoxy-1,2-O-isopropylidene-alpha-D- xylofuranose, 3,7,9,11-tetraoxa-4-thia-10-dimethyl-tricyclo[6,3,0, 0(2,6)]undecane S-dioxide and 23 in a 2:3:7 ratio. Tetraacetate 14 was converted into the alpha-1-bromide 18 as well as into the alpha-1-O-trichloroacetimidate 17. These three compounds were used as donors for the glycosylation with 4-cyanothiophenol, affording the 4-cyanophenyl 2,3,4-tri-O-acetyl-1,5-dithio-alpha- (29) and beta-D-xylopyranoside (30) in different ratios, depending on the reaction conditions. When donor 18 was used in the presence of potassium carbonate, besides 29 and 30 two aryl C-glycosylated-thioglycosides, i.e. 4-cyano-2-(2,3,4-tri-O-acetyl-5-thio-beta-D-xylopyranosyl)phenyl 2,3,4-tri-O-acetyl-1,5-dithio-alpha- and beta-D-xylopyranoside (32 and 33) as well as 4-cyano-2-(2,3,4-tri-O-acetyl-5-thio-beta-D-xylopyranosyl)phenyl disulfide 34 could be isolated as byproducts. Deacetylation of 30 with sodium methoxide in methanol afforded, besides 4-cyano-phenyl 1,5-dithio-beta-D-xylopyranoside (1), the corresponding 4-[(methoxy)(imino)methyl]phenyl glycoside 2. The 4-cyano group of 1 was converted into the 4-aminothiocarbonyl, the 4-(methyl-thio)(imino)methyl, the 4-amidino and the 4-(imino)(hydrazino)methyl group. All of these glycosides showed a significant antithrombotic activity on rats.

High Pressure Diels-Alder Reactions of 2-Vinyl-3,4-Dihydronaphthalene. Synthesis of Cyclopenta[c]- and Indeno[c]Phenanthrenones.

Abstract A new shorter synthesis of 2-vinyl-3,4-dihydro-naphthalene has been described. The Diels-Alder reactions of this diene with 4-acetoxy-2-cyclopenten-1-one, 3-bromoindan-1-one and inden-1-one under high pressure conditions are reported. A two step synthesis of cyclopenta[c]-and indeno[c]phenanthrenones is discussed. Structure analysis by 1 H and 13 C NMR spectroscopy is presented.

AN EFFICIENT SYNTHETIC APPROACH TO SUBSTITUTED PENTA- AND HEXAHELICENES

A two-step synthetic approach to penta- and hexahelicenes substituted at the terminal aromatic rings has been studied. This approach is based on the Diels–Alder reaction of 5,5′,8,8′-tetramethyl-3,3′,4,4′-tetrahydro-[1,1′]-binaphthalene (2b), 3-vinyl-1,2-dihydronaphthalene (5a), 5,8-dimethyl-3-vinyl-1,2-dihydronaphthalene (5b) and 3-vinyl-1,2-dihydrophenanthrene (15) followed by the aromatization of the cycloadducts. This method is flexible, efficient and of wide application to the synthesis of several benzenoid and nonbenzenoid penta- and hexahelicenes. The racemization energy barriers of helicenes 3, 9, 10, 13, 14, 17 and 18 were computed with the semiempirical quantum method AM1. The computed values show that, when methyl groups are introduced at the inner position of the terminal aromatic rings, the racemization barriers increase markedly. A structure analysis of the reaction products by 1H- and 13C-NMR spectroscopy is also presented.

Stereospecific conversion of H-phosphonates into phosphoramidates. The use of vicinal carbon-phosphorus couplings for configurational determination of phosphorus

Abstract Separated P-diastereomers of H-phosphonate diesters gave exclusively one isomer of amidates on treatment with CCl 4 + butylamine with inversion of configuration. NOE experiments and the trend observed in 3 J(C2-P) and 3 J(C4-P) couplings were applied for stereochemical assignment. Separated P-diastereomers of H-phosphonate diesters gave exclusively one isomer of amidates on treatment with CCl 4 + butylamine with inversion of configuration. NOE experiment and the trend observed in 3 J(C2-P) and 3 J(C4-P) couplings were applied for stereochemical assignment

A new short synthetic approach to cyclopentaphenanthrenones

Abstract The Diels-Alder reactions of 4-acetoxy-2-cyclopenten-1-one and 2-bromo-4-acetoxy-2-cyclopenten-1-one with vinylarenes are discussed. The aromatization of the reaction products opens a new two-step route for the synthesis of cyclopentaphenanthrenones. Structure analysis of reaction products by 1 H and 13 C-NMR spectroscopy is reported.

Diels-Alder reactions of arylethenes. Synthesis of some [5]phenacenes and fluorenoanthracenes

Abstract A one-pot high yielding route to 3,4-dihydro-1-(2H)-anthracenone (9) based on high pressure Diels-Alder reaction is described. The synthesis of 3,4-dihydro-1-vinylphenanthrene (1) and 3,4-dihydro-1-vinylanthracene (2) is reported. A new synthetic two-step approach to [5]phenacenes and fluorenoanthracenes has been developed. It is based on the Diels-Alder reaction of arylethenes 1 and 2 with benzyne (13), 1,4-benzoquinone (14), 1,4-naphthoquinone (15) and inden-1-one (17) and on the aromatization of the cycloadducts. Structure analysis of the reaction products by 1H and 13C-NMR spectroscopy is presented.