A computational study to unravel the selectivity in an iron-catalysed [3 + 2] cycloaddition of aziridine and heterocumulenes†
The reaction mechanism of cycloaddition between phenyl aziridine and heterocumulene catalysed by iron salts in water has been modeled computationally to trace the origin of the excellent regioselectivity toward 5-substituted product formation. The calculations reveal that the Lewis-acidic iron centre activates and increases the electrophilicity of the heterocumulene upon binding, so that a nucleophilic aziridine-attack can be invoked. The preferential opening of the substituted C2–N bond in the following intermediate, dictated by the stability of an incipient carbocation is the key for such selectivity. Since the aziridine ring-opening step is asynchronous, concerted in nature, the iminoazoselenolidine ring retains the stereopurity at the chiral carbon.