Trifluoroacetic acid → (4E)-N-Methyl-5-(5-ethoxy-3-pyridyl)-4-penten-2-amine

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Reaction Steps

Under a nitrogen atmosphere, a cold (0–5° C.), stirring solution of (4E)-N-methyl-N-(tert-butoxycarbonyl)-5-(5-ethoxy-3-pyridyl)-4-penten-2-amine (0.67 g, 2.09 mmol) in anisole (10 mL) was treated dropwise over 30 min with trifluoroacetic acid (10.40 g, 91.17 mmol). The resulting solution was stirred for 45 min at 0–5° C. and was then concentrated by rotary evaporation. The light-yellow oil was further dried under high vacuum at 0.5 mm Hg. The resulting oil was cooled (0–5° C.), basified with 10% NaOH solution (10 mL), treated with saturated NaCl solution (7.5 mL), and extracted with CHCl3 (4×10 mL). The combined light-yellow CHCl3 extracts were washed with saturated NaCl solution (20 mL), dried (Na2SO4), filtered, concentrated by rotary evaporation, followed by further drying at 0.5 mm Hg producing a brown oil (0.46 g). The crude product was purified by column chromatography on silica gel (56 g), eluting with CH3OH-Et3N (98:2, v/v). Selected fractions containing the product (Rf 0.35) were combined and concentrated on a rotary evaporator. The residue was dissolved in CHCl3, and the CHCl3 solution was dried (Na2SO4), filtered, concentrated by rotary evaporation, and vacuum dried to give 327.5 mg (71.0%) of a light-yellow oil.

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