PURPOSE: To obtain the titled compound useful as a raw material for medicines, agricultural chemicals, etc. in high yield at a low cost, by hydrogenating isoquinoline in the presence of a nickel catalyst and ruthenium catalyst as a hydrogenation catalyst under given conditions in two stages.
CONSTITUTION: Isoquinoline as a raw material is hydrogenated in the presence of a nickel catalyst at 100W250°C, preferably 160W230°C under ≥20kg/cm 2 .G, preferably ≥100kg/cm 2 .G hydrogen pressure. The resultant 1,2,3,4-tetrahydroisoquinoline is then hydrogenated in the presence of a ruthenium catalyst at 100W230°C, preferably 150W200°C under ≥100kg/cm 2 .G hydrogen pressure to afford the aimed compound. The amount of the above-mentioned nickel catalyst to be used is 5W20% based on the isoquinoline, and the amount of the ruthenium catalyst to be used is preferably 0.1W0.25wt% based on the above-mentioned intermediate product.