Description:
<jats:title>Abstract</jats:title><jats:p>We present a Lewis acid catalyzed nucleophilic ring‐opening of donor‐acceptor cyclopropanes and ‐butanes by sydnones, utilizing their respective 1,3‐ and 1,4‐reactivity. The same conditions can be applied for the addition of sydnones to Michael acceptors. We propose a Friedel‐Crafts like mechanism. The reaction provides a rare, low‐temperature, transition metal‐free, and functional group tolerant protocol for the late‐stage functionalization of these mesoionic compounds of emerging importance in catalysis and bio‐orthogonal chemistry.</jats:p>