title: Diastereoselective Strategies towards Thia[n]helicenes.
abstract: In the present study, we have investigated different strategies for diastereoselective synthesis of thia[n]helicenes. We describe the introduction of different chiral auxiliaries at various positions and investigated their effect in the photocyclization reaction. Different chiral groups were placed at the sterically hindered position of the helical core and their interactions with various solvents and metals like copper were investigated. The use of Cu(I) salts has led to high diastereoselectivity in the photocyclization process and we were successful in obtaining the thia[5]helicene in enantiomerically pure form in good yield. The single diastereomer obtained was characterized by X-ray crystallography. From the study of the barrier of racemization of these thia[5]helicenes, the stability was found to be comparable to unsubstituted tetrathia[7]helicenes and substituted diazadithia[7]helicenes. This approach provides an easy access to enantiopure helicenes.
authors.affiliation: Molecular Design and Synthesis, Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven (Belgium), Fax: (+32) 16327990.
authors.forename: Deepali
authors.initials: D
authors.lastname: Waghray
authors.affiliation: Department of Polymer Chemistry and Technology, Kaunas University of Technology, Barsausko 59, LT-51423 Kaunas (Lithuania).
authors.forename: Gintautas
authors.initials: G
authors.lastname: Bagdziunas
authors.affiliation: Biomolecular Architecture, Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven (Belgium).
authors.forename: Jeroen
authors.initials: J
authors.lastname: Jacobs
authors.affiliation: Biomolecular Architecture, Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven (Belgium).
authors.forename: Luc
authors.initials: L
authors.lastname: Van Meervelt
authors.affiliation: Department of Polymer Chemistry and Technology, Kaunas University of Technology, Barsausko 59, LT-51423 Kaunas (Lithuania).
authors.forename: Juozas Vidas
authors.initials: JV
authors.lastname: Grazulevicius
authors.affiliation: Molecular Design and Synthesis, Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven (Belgium), Fax: (+32) 16327990. wim.dehaen@chem.kuleuven.be.
authors.forename: Wim
authors.initials: W
authors.lastname: Dehaen
keywords: chirality; oxazolines; photocyclization; resolution; thia[5]helicenes