New environmentally-friendly solvent-free synthesis of imines using calcium oxide under microwave irradiation

Condensation of structurally diverse aldehydes including heterocyclic aldehydes, like furfural, with various amines in the presence of calcium oxide affording the corresponding imines in solvent-free conditions in good to excellent yields under microwave irradiation is described. A comparative study has been done under thermal conditions. The synergy between dry media and microwave irradiation in this reaction is evaluated by condensing less electrophilic aldehydes with poorly nucleophilic amines. The main advantages of this environmentally friendly protocol are the use of the non-toxic and inexpensive reagent calcium oxide and the considerable rate enhancement in comparison with a thermal reaction.