Stereoselective Photoredox Catalyzed (3+3) Dipolar Cycloaddition of Nitrone with Aryl Cyclopropane

By resorting to the principle of remote activation, we herein demonstrate the first photoredox catalyzed (3+3) dipolar cycloaddition of nitrones with aryl cyclopropanes. Key to the fidelity of the reaction resides in a facile manner of substrate activation by single-electron transfer (SET) oxidation with photoredox catalysis, and the reaction takes place through a stepwise cascade encompassing a three-electron-type nucleophilic substitution triggered cyclopropane ring-opening and a diastereoselective 6-endo-trig radical cyclization manifold. The reaction proceeds under mild conditions with excellent regio- and stereoselectivity, nicely complementing the well-developed Lewis acid catalyzed cycloaddition of donor-acceptor cyclopropanes. Other merits of the protocol include wide scope of aryl cyclopropanes with diversified substitution patterns and good functional-group compatibility. A mechanism involving an aryl radical cation promoted remote activation mode was also proposed and supported by mechanistic experiments. A radical type (3+3) cycloaddition of cyclopropane is realized with aryl cyclopropane and nitrone under photoredox catalysis in a highly regio- and diastereoselective manner. The reaction includes a stereospecific three-electron-type nucleophilic ring opening and a 6-endo-trig radical cyclization.+image

Automated summary

By using photoredox catalysis, we have achieved the (3+3) dipolar cycloaddition of nitrones with aryl cyclopropanes. This reaction exhibits excellent regio- and stereoselectivity and can be applied to a variety of aryl cyclopropane substrates.