The reaction of methyl-2-oxoglutarate (I) with triethyl orthoformate (A) by means of H2SO4 in refluxing methanol gives methyl 2,2-diethoxyglutarate (II), which is hydrolyzed partially with NaOH in water yielding methyl 2,2-diethoxy-4-carboxybutanoate (III). The reduction of (III) with NaBH4 and BF3 ethearate affords methyl 5-hydroxy-2-oxopentanoate (IV). The controlled oxidation of (IV) with pyridinium chlorochromate and sodium acetate in methylene chloride gives methyl 2,5-dioxopentanoate (V), which is condensed with N-ethyltryptamine (VI) by means of acetic acid in refluxing benzene yielding the tricyclic ketoester (VII). Finally, this compound cyclizes again spontaneously.

The reaction of methyl-2-oxoglutarate (I) with triethyl orthoformate (A) by means of H2SO4 in refluxing methanol gives methyl 2,2-diethoxyglutarate (II), which is hydrolyzed partially with NaOH in water yielding methyl 2,2-diethoxy-4-carboxybutanoate (III). The reduction of (III) with NaBH4 and BF3 ethearate affords methyl 5-hydroxy-2-oxopentanoate (IV). The controlled oxidation of (IV) with pyridinium chlorochromate and sodium acetate in methylene chloride gives methyl 2,5-dioxopentanoate (V), which is condensed with N-ethyltryptamine (VI) by means of acetic acid in refluxing benzene yielding the tricyclic ketoester (VII). Finally, this compound cyclizes again spontaneously.