Ring-Opening Cross-Coupling of Cyclopropanols with Electrophilic Alkenes via Photoinduced Charge Transfer Facilitated by Decatungstate Catalyst

Abstract

A unique property of aryl-substituted tertiary cyclopropanols to form photoactive electron donor-acceptor (EDA) complexes with electron-deficient olefins has been applied for the synthesis of distantly functionalized ketones via redox-neutral addition of cyclopropanol-derived β-ketoalkyl radicals to the electrophilic double bond of the olefins. The reaction occurs upon UV light irradiation that triggers homolytic cleavage of the cyclopropane ring through photoinduced charge transfer in the formed EDA complexes. The reaction rate drastically increases in the presence of tetrabutylammonium decatungstate (TBADT), which facilitates the electron transfer between the reactants and allows the reaction to occur even in the case of cyclopropanols that cannot form EDA complexes. The described transformations proceed under mild conditions and do not require stoichiometric oxidants. The generality and robustness of the developed method have been validated on a broad scope of cyclopropanol and alkene substrates, delivering the corresponding adducts in up to 92% yield. Successful scale up under continuous flow conditions has also been demonstrated.