Microwave-mediated Regioselective Synthesis of Novel Pyrimido[1,2-a]pyrimidines under Solvent-free Conditions

In recent years there has been increasing interest in the design of alkyl 1,4-dihydropyrimidine-5-carboxylates (1,4-DHPMs) and related Biginelli-like compounds [1] which are presented as valuable substitutes [2] for the well known Nifedipine® and other 1,4-dihydropyridine drugs [3] clinically used in the treatment of cardiovascular diseases. That interest is illustrated, i.a., by the disclosure of elegant protocols involving solid phase synthesis approaches [4] as well as solvent-free preparations under microwave irradiation. [5] The purpose of the present work is to extend the scope of those studies to 2-amino derivatives and especially to the evaluation of their synthetic potential for the construction of novel pyrimido[1,2-a]pyrimidines, a ring system that can be found in marine-derived natural products such as crambescidin [6] and batzelladine [7] alkaloids.