4-Benzyloxy-indole-2-carboxylic acid (I) is converted into the corresponding dimethylamide (III), via the corresponding acid chloride (II); the dimethylamide (III) is reduced with LiAlH4 to give 4-benzyloxy-2-dimethylaminomethyl-indole (IV), which is hydrogenated to 4-hydroxy-2-methyl-indole (V). The reaction of (V) with epichlorohydrin (A) in aqueous NaOH gives the crude epoxide which without isolation is treated with isopropylamine (B) in refluxing dioxane.
4-Hydroxy-2-methyl-indole (IV) can be quaternized with MeI yielding the ammonium salt (VI), which by heating with aqueous NaCN in converted into 2-cyanomethyl-4-benzyloxyindole (VII). The hydrolysis of (VII) affords the corresponding acid (VIII), which is decarboxylated to 4-benzyloxy-2-methyl-indole (IX). Finally, this compound is hydrogenated to the previously obtained 4-hydroxy-2-methyl-indole (V).
The reaction of 4-hydroxy-2-methyl-indole (V) with 1-(N-benzylisopropylamino)-3-chloro-2-propanol (D) by means of NaOH in refluxing aqueous dioxane yields the corresponding benzylamine (X), which is debenzylated by catalytic hydrogenation. The reaction of 4-hydroxy-2-methyl-indole (V) with epichlorohydrin (A) and benzylamine (B) gives 4-(3-benzylamino-2-hydroxypropoxy)-2-methyl-indole (XI), which is debenzylated by hydrogenolysis to 4-(3-amino-2-hydroxypropoxy)-2-methyl-indole (XII). The condensation of (XII) with refluxing acetone (C) affords the corresponding N-isopropylidene derivative (XIII), which is finally hydrogenated with H2 over Pd/C in methanol.