Helmut Sonnenschein

Fluorescent anion receptors with iminoylthiourea binding sites—selective hydrogen bond mediated recognition of CO32−, HCO3− and HPO42−

Abstract A number of structurally simple, fluorescent sensor molecules based on the iminoylthiourea/1,2,4-thiadiazole unit are presented, which display extraordinarily strong fluorescence enhancement selectively upon complexation of HCO 3 − , CO 3 2− and HPO 4 2− .

Lipase-catalysed resolution of 3,3′-bi-indolizines: The first preparative access to enantiomerically pure samples

Abstract The lipase-catalysed kinetic resolution of the axially chiral 3,3′-bis[1-(2-hydroxyethyl)-2-phenylindolizine] [(±)-1a] and the corresponding 3-hydroxypropyl derivative (±)-1b by acylation with vinyl acetate in the presence of lipases from different origins has been investigated. For the first time, enantiomerically pure 3,3′-biindolizine derivatives were obtained on a preparative scale by careful monitoring of the conversion.

Separation of enantiomers by lipase-catalyzed fluorous-phase delabeling

Simultaneous enantiomer-selective fluorous-phase delabeling and kinetic resolution was achieved by lipase-catalyzed alcoholysis of highly fluorinated esters of racemic alcohols. The separation of the fast-reacting delabeled enantiomers and the slow-reacting fluorous-phase labeled enantiomers was performed very efficiently by partition in an organic/fluorous biphasic solvent system.

PHOSPHINE- AND PHOSPHITE-SUBSTITUTED 3,3′-BI-INDOLIZINES- NEW ATROPISOMERIC LIGANDS

Abstract For the first time enantiomerically pure phosphine- or phosphite-substituted 1,1′-alkyl-3,3′-bi-indolizines were obtained. In situ prepared rhodium complexes of these compounds were tested in hydroformylation of styrene and methylstyrene.

Switchable electron-rich biindolizine-based macrocycles: synthesis and redox properties

New redox-active cyclophanes, incorporating electrochemically switchable biindolizine units in combination with π-electron-rich hydroquinol units in the ether bridges, have been synthesized by intra- and inter-molecular cyclisation. The electrochemical properties of the cyclophanes, investigated by cyclic voltammetry (CV), are reported. Cyclophanes 5a/6a and 7a, containing 1,4-dioxyphenylene units, showed three reversible redox steps as expected. In contrast, intramolecular interactions occur for cyclophanes 5b/6b and 7b, containing 1,5-dioxynaphthylene as part of the cyclophane ring system. Compounds 5b/6b displayed changes in their electrochemical behaviour upon addition of 2,4,7-trinitrofluoren-9-one but, in general, no influence of potential guests on the half-wave potentials of the biindolizine unit could be established. To have additional possibilities of supramolecular interactions, new 2,2′-heterocycle-disubstituted biindolizines 8 and 9 have been synthesized, which in CV signals a complexation of copper near to the biindolizine redox unit.

Reaction of a N-anthrylcarbonylthiourea derivative with Cu2+ or H+: unusual rearrangement to a highly fluorescent S-(9-anthryl)isothiouronium salt

For the fluorescent ligand 1-(9-anthrylcarbonyl)-3,3-tetramethylenethiourea with Cu(ClO4)2 or strong acids an unusual rearrangement reaction occurred yielding a highly emissive S-(9-anthryl)isothiouronium salt. This rearrangement product was characterised by NMR spectroscopy and X-ray analysis as well as absorption and fluorescence spectroscopy. Additionally, the chemical and complexation behaviour of the N-anthrylcarbonylthiourea derivative is compared to that of its naphthyl and phenyl analogues.

Diastereoisomerism and electrochemical behaviour— an investigation of redox-active cyclophanes

The influence of diastereoisomerism on the electrochemical behaviour of the atropisomeric cyclophanes 1a and 1b was found by cyclovoltammetric studies. Compound 1a can be oxidized and reduced reversibly in a two step redox process similar to that of model compound 2. In contrast, 1b shows a different electrochemistry. As a result of a detailed investigation of 1b a complex reaction scheme can be postulated starting with a chemical reaction after the first oxidation step. The special spatial situation in 1b makes possible this EC mechanism reaction, which does not occur in 1a or in unbridged biindolizines.

Chlorination of enantiomerically pure 1,1′-bis(hydroxyalkyl)-3,3′-biindolizines: conservation of chirality by thermal treatment

Enantiomerically pure 1,1′-bis(hydroxyalkyl)-3,3′-biindolizines 1 racemize unexpectedly by reaction with tetra-chloromethane–triphenylphosphine at room temperature affording the corresponding dichloro compounds 2, whereas the chirality is preserved at higher reaction temperatures.