Sustainable Synthesis of Benzylidenemalononitrile Compounds Under Microwave- Irradiation

A green methodology was developed to obtain a large scope of Knoevenagel adducts with high yields (77-95%). The compounds were synthetized in 30 min, using aromatic aldehyde derivatives, malononitrile, water as a solvent, microwave irradiation as a heating source and in free-catalyst conditions. In a particular case, in the synthesis of the adduct derived from the α-methyl-trans-cinnamaldehyde, a [2+2] photochemical cycloaddition product was observed, a tetrasubstituted cyclobutane dimeric compound 3w’. Its complex structure was confirmed by X-ray diffraction (first time), nuclear magnetic resonance analysis and electronic structure calculations. Theoretical results suggest that the thermal decomposition of 3w’ back to 3w can occur by means of a biradical intermediate.