An enantiopure syn-benzocyclotrimer 1 was selectively synthesized from an enantiopure halonorbornene 2 through regioselective cyclotrimerization catalyzed by palladium nanoclusters. The yield of 1 was dependent on the stability of the palladium clusters, which was ascertained from the appearance and TEM images of the reaction mixtures. The thus-prepared enantiopure benzocyclotrimer will serve as a key intermediate for the synthesis of C-3v symmetric chiral buckybowls.