Tetrahydrofuran → alpha-trimethylsilylethoxymethyl-DL-tryptophan methyl ester

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A solution of DL-tryptophan methyl esterbenzaldimine (4.0 g, 13 mmol) in 30 mL THF was added over 15 minutes to a mixture of 20.2 mL lithiumdiisopropylamide (10% suspension in hexan) and 70 mL dry THF, cooled to -10° C. under nitrogen atmosphere. The stirring was continued for an additional 45 minutes, keeping the temperature at -10° C. A solution of trimethylsilylethoxymethylchloride (2.2 g, 13.2 mmol) in 5 mL THF was added and the mixture stirred overnight at room temperature. The reaction mixture was decomposed with 100 mL distilled water, extracted with ethyl acetate (3×100 mL), and the organic solvent was removed in vacuo. The resulting oily residue was treated with 30 mL IN hydrochloric acid for 1 hour at room temperature after which the reaction mixture was made basic with sodium bicarbonate and extracted with ethyl acetate (3×100 mL). The organic layer was dried over Na2SO4, evaporated to give the crude product which was separated by flash chromatography on silica gel using a mixture of toluene/ethanol 500:30 (v/v) as elution solvent. The fractions, containing the main product (TLC on silica gel, toluene/ethanol 10:2 (v/v), Rf 0.38) were combined and evaporated to dryness in vacuo. Trituration of the oily residue with diethyl ether gave 2.0 g (44%) of α-trimethylsilylethoxymethyl-DL-tryptophan methyl ester, mp 113°-115° C.

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