The title compound, C(21)H(26)N(2)O, was obtained as an unexpected by-product when attempting to prepare (S)-2-benzyl-N-tert-butyl-1,2,3,4-tetra-hydro-isoquinoline-3-carboxamide from (S)-2-benzyl-amino-N-tert-butyl-3-phenyl-propanamide and dimethoxy-methane. The mol-ecules are linked by weak C-H⋯O hydrogen bonds, generating linear chains parallel to the b axis. C-H⋯π inter-actions provide further stability for the crystal structure. The planes of the two phenyl rings make a dihedral angle of 84.1 (1)°. The absolute configuration was known from the starting material.