Aromatization of 1,6,7,7a-tetrahydro-2H-indol-2-ones by a novel process.: Preparation of key-intermediate methyl 1-benzyl-5-methoxy-1H-indole-3-acetate and the syntheses of serotonin, melatonin, and bufotenin

Imine 7 of 1,4-cyclohexanedione mono-ethylene ketal 6 was reacted with maleic anhydride, affording the cyclized adduct 8. Methyl esterification of 8, accompanied by transacetalization, led to the dihydrooxindole derivative 10. Aromatization of 10 was then accomplished with POCl3, leading directly to the key-intermediate title compound 11 in 74% yield from ketone 6. Serotonin, melatonin, and bufotenin were then obtained by standard reactions.