Synthesis of Spiropyrrolines <i>via</i> One-Pot\nTf<sub>2</sub>O‑Mediated Amide Activation/Formal [3 + 2]-Cycloaddition\nof α‑Formylamino Ketones

An\nefficient method for the synthesis of spiropyrrolines\nfrom readily\naccessible α-formylamino ketones is reported. The method involves\namide activation using Tf<sub>2</sub>O, followed by a formal [3 +\n2]-cycloaddition of the resulting enolic nitrilium intermediate with\nMichael acceptors, ultimately affording spiropyrrolines. Mechanistic\ninsights were gained through NMR studies, elucidating the precise\nrole of the base additive and suggesting the formation of an enolic\nnitrilium intermediate.