To a stirred solution of 162.2 g (0.50 mol) of (E)-6-benzyloxy-2-nitro-β-pyrrolidinostyrene in 1 L of THF and 1 L of methanol at 30°C under nitrogen is added 10 mL of Raney nickel followed by 44 mL (0.75 mol) of 85% hydrazine hydrate. Vigorous gas evolution is observed. The red color turns dark brown within 10 minutes, and the reaction temperature rises to 46°C. An additional 44 mL of 85% hydrazine hydrate is added after 30 min and again 1 hr later. The temperature is maintained between 45 and 50°C with a water bath during the reaction and for 2 hr after the last addition. The mixture is cooled to room temperature, and the catalyst is removed by filtration through a bed of Celite. The catalyst is washed several times with methylene chloride. The filtrate is evaporated, and the residue is dried by evaporating with 500 mL of toluene. The reddish residue (118.5 g), dissolved in ca. 1 L of toluene-cyclohexane (1 : 1), is applied to a column of 500 g of silica gel (70–230-mesh, Merck) prepared in the same solvent. Elution with 6.0 L of toluene–cyclohexane (1 : 1) followed by 3 L of toluene–cyclohexane (1 : 2) affords 108.3 g of white solid, which is crystallized from 150 mL of toluene and 480 mL of cyclohexane. 107.3 g (96% yield) of 4-benzyloxyindole is obtained in three crops as white prisms, mp 60–62°C.
