andreas ostrowicki - Academia.edu (original) (raw)
Uploads
Papers by andreas ostrowicki
Journal of The Chemical Society, Chemical Communications, 1989
This overview highlights the application of the “cesium effect” in synthetic reactions. Special a... more This overview highlights the application of the “cesium effect” in synthetic reactions. Special attention is drawn to macrocyclizations. More recent examples published between 1983 and 1990 are selected critically. In a short introduction cesium salts which are usually applied in organic chemistry are introduced, followed by many concrete examples of the use of cesium salts in ring closure reactions leading to macro- and oligomacrocyclic compounds. It is shown that by using cesium salts instead of the corresponding sodium and potassium compounds in ring closure reactions yields can often be dramatically increased. The review is concluded with attempts to explain the special effects of cesium salts in organic synthesis.
Synthesis-stuttgart, 1988
Pure and Applied Chemistry, 1990
European Journal of Inorganic Chemistry, 1990
Chiral Triple-Layered and Condensed [2.2]Cyclophanes - Synthesis, Structure, Chiroptical Properti... more Chiral Triple-Layered and Condensed [2.2]Cyclophanes - Synthesis, Structure, Chiroptical PropertiesThe helical title compounds 1-5 are obtained using a simple one-step cyclisation reaction with yields reaching or increasing those obtained by application of organometallic methods in [2.2]phane syntheses. The formation of the triple-layered phanes 1 leads with high selectivity only to the “up-down” isomers with fixed conformation, as shown by X-ray crystallography and by the detection of strong NOEs of the inner hydrogen atoms. For studies on structure-chiroptic relation-ships a systematic sequence of helical [2.2]phanes with larger arene systems is synthesized. Enrichment of enantiomers is achieved by HPLC on (+)-PTrMA; the kinetics of racemisation and the CD spectra are discussed.
![Research paper thumbnail of Intra- und extraannular funktionalisierte helical-chirale [2.2]Metacyclophane: Synthese, Circulardichroismus und Struktur-Chiroptik-Beziehungen](https://attachments.academia-assets.com/48518752/thumbnails/1.jpg)
](European Journal of Inorganic Chemistry, 1990
Intra- und Extraannularly Functionalized Chiral [2.2]Metacyclophanes: Synthesis, Circular Dichroi... more Intra- und Extraannularly Functionalized Chiral [2.2]Metacyclophanes: Synthesis, Circular Dichroism, and Structure - Chiroptic RelationshipsA simple one-step cyclization reaction for the synthesis of the title compounds 1-5 is presented; separation (enrichment) of enantiomers is achieved by HPLC mainly on (+)-PTrMA. The kinetics of interconversion (racemization) of the new dihetera[2.2]metacyclophanes are determined: No racemization of the internally substituted phanes is found on heating until decomposition, whereas the extraannularly substituted compounds exhibit barriers of interconversion of about 130 kJ/mol, similar to that of the unfunctionalized skeleton 1a. For the pyridinophane 2 the barrier (110 kJ/mol) is lower corresponding to the decreased spatial requirement of the nitrogen lone pair compared to a C-H bond. The circular dichroism curves of the intraannularly functionalized phanes are compared with those of the extraannularly functionalized reference compounds: A bathochromic shift of the Cotton effect at short wavelengths is found, which is increasing with the bulkiness of the internal functional group.
Acta Chemica Scandinavica, 1990
Journal of The Chemical Society, Chemical Communications, 1989
This overview highlights the application of the “cesium effect” in synthetic reactions. Special a... more This overview highlights the application of the “cesium effect” in synthetic reactions. Special attention is drawn to macrocyclizations. More recent examples published between 1983 and 1990 are selected critically. In a short introduction cesium salts which are usually applied in organic chemistry are introduced, followed by many concrete examples of the use of cesium salts in ring closure reactions leading to macro- and oligomacrocyclic compounds. It is shown that by using cesium salts instead of the corresponding sodium and potassium compounds in ring closure reactions yields can often be dramatically increased. The review is concluded with attempts to explain the special effects of cesium salts in organic synthesis.
Synthesis-stuttgart, 1988
Pure and Applied Chemistry, 1990
European Journal of Inorganic Chemistry, 1990
Chiral Triple-Layered and Condensed [2.2]Cyclophanes - Synthesis, Structure, Chiroptical Properti... more Chiral Triple-Layered and Condensed [2.2]Cyclophanes - Synthesis, Structure, Chiroptical PropertiesThe helical title compounds 1-5 are obtained using a simple one-step cyclisation reaction with yields reaching or increasing those obtained by application of organometallic methods in [2.2]phane syntheses. The formation of the triple-layered phanes 1 leads with high selectivity only to the “up-down” isomers with fixed conformation, as shown by X-ray crystallography and by the detection of strong NOEs of the inner hydrogen atoms. For studies on structure-chiroptic relation-ships a systematic sequence of helical [2.2]phanes with larger arene systems is synthesized. Enrichment of enantiomers is achieved by HPLC on (+)-PTrMA; the kinetics of racemisation and the CD spectra are discussed.
European Journal of Inorganic Chemistry, 1990
Intra- und Extraannularly Functionalized Chiral [2.2]Metacyclophanes: Synthesis, Circular Dichroi... more Intra- und Extraannularly Functionalized Chiral [2.2]Metacyclophanes: Synthesis, Circular Dichroism, and Structure - Chiroptic RelationshipsA simple one-step cyclization reaction for the synthesis of the title compounds 1-5 is presented; separation (enrichment) of enantiomers is achieved by HPLC mainly on (+)-PTrMA. The kinetics of interconversion (racemization) of the new dihetera[2.2]metacyclophanes are determined: No racemization of the internally substituted phanes is found on heating until decomposition, whereas the extraannularly substituted compounds exhibit barriers of interconversion of about 130 kJ/mol, similar to that of the unfunctionalized skeleton 1a. For the pyridinophane 2 the barrier (110 kJ/mol) is lower corresponding to the decreased spatial requirement of the nitrogen lone pair compared to a C-H bond. The circular dichroism curves of the intraannularly functionalized phanes are compared with those of the extraannularly functionalized reference compounds: A bathochromic shift of the Cotton effect at short wavelengths is found, which is increasing with the bulkiness of the internal functional group.
Acta Chemica Scandinavica, 1990