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.