Rapid Access to Polyfunctionalized 3,4-Dihydroquinazolinones through a Sequential N-Acyliminium Ion Mannich Reaction Cascade

A microwave-promoted one-pot, three-component sequential cyclization-Mannich reaction of unactivated ketones, o-formyl carbamates and primary amines has been developed. Cyclic N-acyliminium ions are generated in situ from the carbamate and amine starting materials. This metal-free cascade protocol provides rapid access to structurally diverse 3,4-dihydroquinazolinones in good to excellent yields with high regioselectivity for the terminal methyl group, in the case of unsymmetrical methyl alkyl ketones. Key features of the developed protocol include its operational simplicity, ease of product purification, and wide functional group tolerance.