Pyrene-Fused [7]Helicenes Connected Via Hexagonal and Heptagonal Rings: Stereospecific Synthesis and Chiroptical Properties
Asim Kumar Swain, Krzysztof Radacki, Holger Braunschweig, Prince Ravat
Abstract
In this manuscript, we portrayed a stereospecific synthesis of C 2 - and C 1 -symmetric pyrene-fused [7]helicene compounds 1 and 2, respectively. Compounds 1 and 2 were synthesized via a one-pot Suzuki coupling–C–H activation and two-step Suzuki coupling–Scholl reaction, respectively, with complete retention of configuration. The synthesized molecules differ in the fusing mode of [7]helicene units with pyrene via six- and seven-membered rings for 1 and 2, respectively. There was a significant difference in the functional properties and enantiomerization barrier of both compounds because of their distinct molecular symmetry as well as fusing mode to pyrene moiety. The heptagon-containing molecule 2 showed remarkable photophysical and chiroptical properties with commendable configurational stability compared to 1 and pristine [7]helicene as well as its [5]helicene congener.