Abstract
Transition metal-catalyzed C–H activation and radical reactions are two versatile strategies to construct diverse organic skeletons. Here we show the construction of a class of flavylium fluorophores via the merge of radical chemistry and C–H activation starting from (hetero)aryl ketones and alkynes. This protocol is not only applicable to aryl ketones but also to heteroaryl ketones such as thiophene, benzothiophene and benzofuran, thus leading to structural diversity. Mechanism studies, including control experiments, intermediate separation, radical trapping, EPR and ESI-HRMS experiments, demonstrate that the key step lies in the addition of the acyl radical generated by the copper-catalyzed C–C bond cleavage of aryl ketone to the rhodacycle formed via the C–H activation of aryl ketone. The flavylium fluorophores feature butterfly symmetrical configuration, nearly planar skeleton and delocalized positive charge, and exhibit intriguing photophysical properties, such as tunable absorption and emission wavelengths and high quantum yields.
Highlights
Transition metal-catalyzed C–H activation and radical reactions are two versatile strategies to construct diverse organic skeletons
Oxygen-doped fluorophores based on pyrylium framework begin to attract attention because of tunable emission wavelength, high quantum yield and water solubility, making them as ideal optical-imaging reagents (Fig. 1b)[8,9,10,11,12,13]
Density functional theory (DFT) calculation was employed to evaluate the intrinsic characteristic of cationic 3aa (Supplementary Data 1)[37,38]
Summary
Transition metal-catalyzed C–H activation and radical reactions are two versatile strategies to construct diverse organic skeletons. Oxygen-doped fluorophores based on pyrylium framework begin to attract attention because of tunable emission wavelength, high quantum yield and water solubility, making them as ideal optical-imaging reagents (Fig. 1b)[8,9,10,11,12,13]. From both the fundamental and application viewpoints, a study of the structural diversity of organic fluorophores is doubtlessly of great importance. Carbohelicenes were synthesized by a C–H activation/radical approach/C–H activation relay of α-acetylnaphthalenes with alkynes[35]
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