Intramolecular cycloadditions of nitrones derived from optically active 1-alkenyl-2-imidazolecarbaldehydes: regio- and diastereoselectivity

Enantiopure polyfunctionalized imidazo[1,2-a]pyridines and pyrrolo[1,2-a]imidazoles, two classes of heterocyclic compounds including anti-inflammatories and glycosidase inhibitors, were synthesized starting from natural α-aminoacids and exploiting an intramolecular nitrone cycloaddition as the key step. The regiochemistry of the cycloaddition, which determines the product distribution, was markedly dependent on the R substituent and, therefore, submitted to a theoretical study by means of ab initio and MP2 calculations.