Potassium Hydroxide → 6-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole

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Reaction Steps

To a solution of potassium hydroxide (16 g) in methanol were added at 5° C. 4-piperidone hydrate hydrochloride (30 g) and a solution of 6-methyl-1H-indole (10 g) in methanol (50 ml). The mixture was refluxed for 16 hours. After cooling precipitated inorganic salts were filtered off. Methanol was evaporated and the remaining oil was dissolved in ethyl acetate (200 ml) and subsequently washed with brine (2×100 ml). After drying (anh. MgSO4) the solvent was evaporated leaving 15 g of crude 6-methyl-3-(1,2,3,6-tetrahydro-4-pyridyl)-1H-indole, which was used without further purification. The pure tetrahydropyridyl derivative crystallized from diethyl ether. Mp: 150°-152° C. To a solution of 1-(2-chloroethyl)-3-(2-propyl)-2-imidazolidinon (32 g) in MIBK (500 ml) were added 6-methyl-3-(1,2,3,6-tetrahydro-4-pyridyl)-1H-indole (15 g), potassium carbonate (16 g) and potassium iodide (5 g). The mixture was refluxed for 19 hours and finally filtered while still hot. MIBK was evaporated and the resulting oil was dissolved in ethyl acetate (500 ml) and washed with brine (2×100 ml). After drying (anh. Na2SO4) ethyl acetate was evaporated. The remaining oil was stirred with diethyl ether (200 ml) and the precipitated, crystalline 3-[1-[2-[3-(2-propyl)-2-imidazolidinon-1-yl]ethyl]-1,2,3,6-tetrahydro-4-pyridyl]-6-methyl-1H-indole was filtered off. Yield: 14.5 g. Mp: 170°-174° C. To a solution of the thus prepared imidazolidinon derivative (14 g) in acetic acid (300 ml), was added PtO2 (600 mg). This mixture was hydrogenated in a Parr apparatus at 3 atm. for 72 hours. The catalyst was filtered off and most of the acetic acid was evaporated in vacuo. The remaining oil was dissolved in H2O and pH was adjusted to 9-10 by addition of dil. NaOH solution. The title compound 14a was extracted with dichloromethane (2×200 ml) and isolated as above. The crude product was purified by eluting (eluent:ethyl acetate/dichloromethane/ethanol/triethylamine (40:40:20:5) through silica gel. Yield: 4.5 g. Mp: 185° C.

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