Synthetic approach to imidazo[1,2-a]pyridine derivatives by the intramolecular nitrone cycloaddition methodology

N-Benzyl and (R)-N-(α-phenylethyl) nitrones derived from 1-allyl-2-imidazolecarbaldehyde underwent intramolecular cycloaddition to give predominantly bridged-ring products, namely 5,6,8,9-tetrahydro-6,9-methanoimidazo[2,1-d][1,2,5]oxadiazepine derivatives. Catalytic hydrogenation of the latter furnished both racemic and enantiopure 6,8-functionalised 5,6,7,8-tetrahydro-imidazo[1,2-a]pyridines.