Preparation and Physicochemical Properties of [6]Helicenes Fluorinated at Terminal Rings

0501626 - ÚCHP 2020 RIV US eng J - Journal Article
Církva, Vladimír - Jakubík, Pavel - Strašák, Tomáš - Hrbáč, J. - Sýkora, Jan - Císařová, I. - Vacek, J. - Žádný, Jaroslav - Storch, Jan
Preparation and Physicochemical Properties of [6]Helicenes Fluorinated at Terminal Rings.
Journal of Organic Chemistry. Roč. 84, č. 4 (2019), s. 1980-1993. ISSN 0022-3263. E-ISSN 1520-6904
R&D Projects: GA ČR(CZ) GA17-02578S; GA ČR GA15-12719S
Institutional support: RVO:67985858
Keywords : helicene * fluorinated * photocyclization
OECD category: Organic chemistry
Impact factor: 4.335, year: 2019
Method of publishing: Limited access

The first racemization-stable helicene derivatives fluorinated at terminal rings, 1,2,3,4-tetrafluoro[6]helicene (6) and 1,2,3,4,13,14,15,16-octafluoro[6]helicene (15), were synthesized via the Wittig reaction followed by oxidative photocyclization in an overall yield of 41% of 6 and 76% of 15. The changed electronic structure in fluorinated helicenes was reflected in a slight shift of UV−vis absorption, fluorescence excitation, and emission spectra maxima when compared to unsubstituted [6]helicene. Cyclic voltammetry revealed a moderate decrease in the HOMO−LUMO gap with increasing fluorination. The specific rotation of tetrafluoro[6]helicene 6 enantiomers was found to be approximately 25% lower than that of unsubstituted [6]helicene. The theoretical study of the racemization barrier suggested a shift toward higher energy with increasing fluorination. The increasing fluorination also significantly affected the intermolecular interactions in the crystal lattice. The observed CH···F interactions led to the formation of 1D-molecular chains in the crystal structures of both fluorinated helicenes.
Permanent Link: http://hdl.handle.net/11104/0294045