Yonemitsu-type condensations catalysed by proline and Eu(OTf)3

We report a Yonemitsu-type trimolecular condensation of aromatic heterocycles, aldehydes, and active methylene compounds to afford polyfunctionalised heterocycles. The reaction is catalysed by L-proline and Eu(OTf)3, takes place in methanol at room temperature, and in some cases is highly diastereoselective (d.e. >90%). The reaction offers two advantages with respect to the previously reported Ti(IV)-promoted condensation: (1) it adheres to some principles of green chemistry, and (2) it provides access to compounds that cannot be obtained by classical methodology.