To a suspension of 1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-carboxaldehyde, oxime (1.0 g, 2.9 mmol) in 15 ml of acetic acid is added 0.9 g (14.6 mmol) of sodium cyanoborohydride (0.9 g, 14.6 mmol). The reaction mixture is stirred vigorously for three hours whereupon an additional 0.35 g (5.6 mmol) of the reducing agent is added. After an additional 45 minutes the reaction mixture is diluted with ethyl acetate and methylene chloride, cooled to 0° C., and 300 ml of a saturated solution of sodium bicarbonate is added dropwise while continuing to stir vigorously. This mixture is diluted further with 400 ml of ethyl acetate and separated from the aqueous phase (pH=9). The organic phase is washed again with a saturated solution of sodium bicarbonate, water, and finally a saturated solution of sodium chloride. It is dried over magnesium sulfate, filtered, and concentrated to a yellow oil which is crude 1-(4-chlorobenzoyl)-N-hydroxy-5-methoxy-2-methyl-1H-indole-3-methanamine and is used without further purification in the subsequent reaction. Mass balance is quantitative. A sample recrystallized from methylene chloride has a mp of 164°-165° C. (dec).
