Ring-Opening Coupling Reaction of Cyclopropanols with Electrophilic Alkenes Enabled by Decatungstate as Photoredox Catalyst

We introduce a methodology for the photocatalytic generation of beta-ketoalkyl radicals from tertiary cyclopropanols, utilizing tetrabutylammonium decatungstate (TBADT) as a photoredox catalyst. The application is demonstrated by the synthesis of distantly functionalized ketones via the redox-neutral addition of the cyclopropanol-derived beta-ketoalkyl radicals to the double bond of electrophilic olefins. The transformation occurs under ambient temperature conditions and is suitable for coupling a wide range of cyclopropanol and alkene substrates. This was demonstrated by the preparation of 33 ketone products with 35-92% yield. The method's preparative robustness has been validated through upscaled preparations conducted under continuous flow conditions. Mechanistic investigations support the role of TBADT as a photoredox catalyst, which facilitates the single electron oxidation of cyclopropanols, followed by the electron transfer from the reduced form of decatungstate to the electrophilic double bond of alkene. Moreover, we found that electron-rich aromatic cyclopropanols and electron-deficient olefins form photoactive electron donor-acceptor (EDA) complexes. This property allows the reaction to proceed under UV light irradiation via the photoinduced charge transfer in the absence of the photocatalyst. image

Automated summary

We present a methodology for photocatalytic generation of beta-ketoalkyl radicals from tertiary cyclopropanols, using TBADT as a photoredox catalyst. The method allows for redox-neutral addition of the radicals to olefins, resulting in the synthesis of distantly functionalized ketones. The reaction occurs under ambient temperature conditions and is compatible with various cyclopropanol and alkene substrates. Mechanistic investigations reveal the role of TBADT as a photoredox catalyst and the formation of electron donor-acceptor complexes between certain cyclopropanols and olefins.