Functionalization of Sydnones with Donor‐Acceptor Cyclopropanes, Cyclobutanes, and Michael Acceptors

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. We present an easy one‐fits‐all, transition metal‐free protocol for a Friedel‐Crafts type functionalization of sydnones with donor‐acceptor cyclopropanes, cyclobutanes, and Michael acceptors. Yields range from moderate to excellent and are indifferent to scale‐up. The products can be of use to the emerging field of bio‐orthogonal sydnone chemistry.