Multicomponent Synthesis of 4-Aryl-4,9-dihydro-1-pyrazolo[3,4-]quinolines Using L-Proline as a Catalyst-Does It Really Proceed?

Looking for effective synthetic methods for 1-pyrazolo[3,4-]quinolines preparation, we came across a procedure where, in a three-component reaction catalysed by L-proline, 4-aryl-4,9-dihydro-1-pyrazolo[3,4-]quinolines are formed. These compounds can be easily oxidised to a fully aromatic system, which gives hope for a synthetic method that could replace, e.g.