A series of tetrahydroimidazo[1,2-a]pyridine derivatives were synthesized by the reaction of 2-vinyl-4,5-dihydroimidazole derivatives with substituted benzylidenemalononitrile via a catalyst-free aza-Diels-Alder reaction. Insecticidal activities of target compounds were tested against pea aphids ( Aphis craccivora ), which showed that activities were strongly influenced by the substituents and their positions. Especially, the introduction of a fluoro group at the 2- position increased activities.