This compound can be prepared by two related ways: 1) The condensation of methoxyacetaldehyde (I) with isopropylamine (II) gives methoxyacetaldehyde isopropylimine (III), which is treated with 4-benzyloxyindole (IV) in acetic acid yielding 4-benzyloxy-3-(1-isopropylamino-2-ethoxyethyl)indole (V). The reaction of (V) with ethyl nitroacetate (VI) in hot toluene affords ethyl 3-(4-benzyloxyindol-3-yl)-2-nitro-5-oxahexanoate (VII), which is reduced with H2 over Raney-Ni in ethanol giving ethyl 3-(4-benzyloxyindol-3-yl)-2-amino-5-oxahexanoate (VIII). Finally, this compound is cyclized with paraformaldehyde (IX) in refluxing benzene. 2) Compound (VIII) can also be cyclized with glyoxylic acid (X) yielding a mixture of the tetrahydrocarboline (XI) and the dihydrocarboline (XII), which, without separation, are decarboxylated and dehydrogenated with sulfur at 140 C.