Sulfur hexafluoridei si nert, non-toxic, and cannot simplyb e applieda sp entafluorosulfanylation reagent. We present the first photoredoxc atalytic way to convert it into pentafluorosulfanylated a-methyl and a-phenyl styrenes simply by using light. Thew ork tacklest he challenges of precise activation of sulfur hexafluorideb yaphotoredox catalystw ith designed consecutive electron transfer cycles in af ashiont hat styrenes trap the generated pentafluorosulfanyl radical. The method overcomes the highly problematic access to vinylica nd allylic pentafluorosulfanyls tyrenes andc ombines it with the disposal of the most potent greenhouse gas.T ogether with the use of light as energy source,a ne xceptionally high level of sustainability is gained.
Results and DiscussionThe conventional photochemical activation of SF 6 requires highly energetic UV light (185 nm =^650 kJ mol À1 )i nt he presence of styrene and yields only SiF 4 and sulfur as products. [15] [a]
SF6 was applied as pentafluorosulfanylation reagent to prepare ethers with a vicinal SF5 substituent through a one‐step method involving photoredox catalysis. This method shows a broad substrate scope with respect to applicable alcohols for the conversion of α‐methyl and α‐phenyl styrenes. The products bear a new structural motif with two functional groups installed in one step. The alkoxy group allows elimination and azidation as further transformations into valuable pentafluorosulfanylated compounds. These results confirm that non‐toxic SF6 is a useful SF5 transfer reagent if properly activated by photoredox catalysis, and toxic reagents are completely avoided. In combination with light as an energy source, a high level of sustainability is achieved. Through this method, the proposed potential of the SF5 substituent in medicinal chemistry, agrochemistry, and materials chemistry may be exploited in the future.
A new range of N-phenylphenothiazine derivatives was synthesized as potential photoredox catalysts to broaden the substrate scope for the nucleophilic addition of methanol to styrenes through photoredox catalysis. These N-phenylphenothiazines differ by their electron-donating and electron-withdrawing substituents at the phenyl group, covering both, σ and π-type groups, in order to modulate their absorbance and electrochemical characteristics. Among the synthesized compounds, alkylaminylated N-phenylphenothiazines were identified to be highly suitable for photoredox catalysis. The dialkylamino substituents of these N-phenylphenothiazines shift the estimated excited state reduction potential up to −3.0 V (vs SCE). These highly reducing properties allow the addition of methanol to α-methylstyrene as less-activated substrate for this type of reaction. Without the help of an additive, the reaction conditions were optimized to achieve a quantitative yield for the Markovnivkov-type addition product after 20 h of irradiation.
Virtually inert sulfur hexafluoride becomes a precious pentafluorosulfanylation agent, if properly activated by photoredox catalysis, to access α-fluoro and αalkoxy SF 5 -compounds. This advanced protocol converts SF 6 in the presence of alkynols as bifunctional CÀ C-and CÀ Obond forming reagents directly into pentafluorosulfanylated oxygen-containing heterocycles in a single step from α-substituted alkenes. The proposed mechanism is supported by theoretical calculations and gives insights not only in the pentafluorosulfanylation step but also into formation of the carbon-carbon bond and is in full agreement with Baldwin's cyclization rules. The key step is a radical type 5-, 6-respectively 7-exo-dig-cyclization. The synthesized oxaheterocycles cannot be simply prepared by other synthetic methods, show a high level of structural complexity and significantly expand the scope of pentafluorosulfanylated building blocks valuable for medicinal and material chemistry.
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