Scheme 1

Synthesis of molecules 3a-e and 4a-d; Reagents and conditions: (i) Ethanol/ H₂O, piperidine, stirring at 80 °C, 4 h; (ii) acetaldehyde, (iii) 2,4- dichlorobenzaldehyde, (iv) N-dimethylaminobenzaldehyde, (v) 4-(benzyloxy)benzaldehyde, (vi) 4-formylphenyl acetate