A slurry of 10.36 g of 1-(2-aminophenyl)-1'-methylspiro[indoline-3,4'-piperidine]dihydrochloride of Example 1b in 60 ml of chloroform is treated portionwise with 12.3 ml of triethanolamine. The resulting mixture is cooled in an ice bath and treated dropwise over 40 minutes with a solution of 2.7 ml of ethyl chloroformate in 20 ml of chloroform. After stirring at room temperature for 1 hour, an additional 3.0 ml of ethyl chloroformate is added and the mixture is permitted to stand 16 hours. The product is washed thrice with water, brine, dried over anhydrous sodium sulfate, concentrated and pumped on under high vacuum to give a crude carbamate. Chromatography on silica gel (100 g) using ether-methylene chloride affords an oil. The material crystallizes on prolonged standing to yield 1-[2-(ethoxycarbonyl)aminophenyl]-1'-methylspiro[indoline-3,4'-piperidine], mp 99.5°-101.0° C.
