Addition reaction of 3,4-dihydroisoquinolines with γ-hydroxy-α,β-unsaturated ketones furnished a variety of diastereomerically pure oxazolo[2,3-a]tetrahydro-isoquinolines, which could be purified by either recrystallization or solvent evaporation. The reaction proceeded smoothly under “green” conditions without an additive and catalyst, giving the target molecules in good to excellent yields.