Thioether-Substituted Hexa-peri-hexabenzocoronenes

The synthesis of novel mono-, di-, tri-, tetra-, and hexafluorinated hexa-peri-hexabenzocoronenes (HBCs) and their conversion into their thioether-substituted analogs is reported. The substitution reaction with the corresponding thiolates was performed microwave-assisted to significantly reduce the reaction time. With increasing amount of fluorination or thioether-substituents, a decreasing extinction coefficient can be observed for the HBCs. Successive addition of thioether-moieties leads to a bathochromic shift of the absorption and emission bands, whereas the nature of the attached thioether does not affect the optoelectronical properties. To further tune the electronic environment of the HBC core, a successive oxidation to the corresponding sulfone as well as the formation of the sulfonium salts were performed. With that, the electron-donating thioethers were transformed into electron-withdrawing substituents, resulting in an inversed electron demand in the periphery of the core. The so obtained compounds showed decreased extinction coefficients and a broadening of the absorption and emission bands.     

The first example of fluoro-Meinwald rearrangement

Novel fluorinated norbornadienes were synthesized in up to 95% yield by the base-induced elimination of HNO₂ from 5-fluoro-5-nitro-6-arylbicyclo[2.2.1]hept-2-enes prepared, in turn, by the Diels–Alder reaction of β-fluoro-β-nitrostyrenes with cyclopentadiene. The subsequent epoxidation initiated the Meinwald type rearrangement affording 6-aryl-bicyclo[3.1.0]hex-2-ene-6-carboxylic acid fluorides as individual (1SR,5RS,6RS)-diastereomers. The transformation is the first example of fluoro-Meinwald rearrangement to form the corresponding acyl fluorides.