Photoredox Catalytic Activation of Sulfur Hexafluoride for Pentafluorosulfanylation of α‐Methyl‐ and α‐Phenyl Styrene

Abstract

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]

Photoredox Catalytic α‐Alkoxypentafluorosulfanylation of α‐Methyl‐ and α‐Phenylstyrene Using SF6

“…Herein, we report an advanced photoredox catalytic method for the activation of SF 6 , which not only pentafluorosulfanylates α‐methyl‐ ( 1 ) and α‐phenyl‐ ( 2 ) styrenes but additionally forms a C−O bond, which significantly broadens the synthetic scope and opens the way for the functionalization of SF 5 building blocks. In contrast to fluorination, our approach precisely controls the local reductivity by N‐phenylphenothiazine ( 3 ) as a strong photoredox catalyst in order to transfer the SF 5 group to α‐methyl‐ ( 1 ) and α‐phenyl‐ ( 2 ) styrenes to yield products 4 and 5 . Mechanistic investigations revealed a two‐fold excitation process (Figure ), similar to the conPET process reported by the König group .…”

“…This mode of reactivity was explored recently by Jamison and McTeague, as well as by Rueping and co‐workers, who reported deoxyfluorination‐type chemistry under photoredox conditions (Figure ) . We unlocked the complementary mode of activation of SF 6 for pentafluorosulfanylation of α‐substituted styrenes …”

“…However, formation of the C−S bond still requires the use of extraordinarily toxic reagents, like S 2 F 10 , and the mixed‐sulfur halogenides SF 5 Cl and SF 5 Br. In contrast, reports on non‐toxic SF 6 in synthesis are rare although this would have strong environmental advantages . SF 6 is still indispensable as an insulating gas in technical applications, like high‐voltage gears, and as a protecting gas in the production of metals.…”

Photoredoxkatalytische α‐Alkoxypentafluorosulfanylierung von α‐Methyl‐ und α‐Phenylstyrol mithilfe von SF6

“…Im Gegensatz zu den Desoxyfluorierungen kontrolliert unser Ansatz die lokalen Reduktionseigenschaften durch den starken Photoredoxkatalysator N‐Phenylphenothiazin ( 3 ), um die SF 5 ‐Gruppe auf α‐Methyl‐ ( 1 ) und α‐Phenylstyrol ( 2 ) zu übertragen und 4 bzw. 5 zu erhalten . Die mechanistischen Untersuchungen ergaben einen zweifachen Anregungsprozess (Abbildung ), ähnlich dem conPET‐Prozess, der von König berichtet wurde .…”

“…Die einfache Zugabe von MeOH zur Reaktionsmischung bestehend aus 1 oder 2 , Katalysator 3 und SF 6 in MeCN ergab die Methylether 8 oder 9 . Die zuvor beobachtete Dimerisierung von 2 wurde vollständig unterdrückt, was wahrscheinlich am schnellen Abfangen von 2 .+ durch MeOH liegt. Der letzte Schritt zur Pentafluorosulfanylierung ist das einfache Abfangen der entstandenen Radikale 6 .…”