[CH3:1][O:2][C:3]1[CH:4]=[CH:5][C:6]([CH:13]2[CH2:18][CH2:17][CH2:16][NH:15][CH2:14]2)=[C:7]2[C:11]=1[NH:10][C:9](=[O:12])[CH2:8]2.[CH2:19]=O.[BH4-].[Na+]>CO.O>[CH3:1][O:2][C:3]1[CH:4]=[CH:5][C:6]([CH:13]2[CH2:18][CH2:17][CH2:16][N:15]([CH3:19])[CH2:14]2)=[C:7]2[C:11]=1[NH:10][C:9](=[O:12])[CH2:8]24.5 g of the product of Example 1 were dissolved in 100 ml of methanol with stirring under an inert atmosphere and after cooling to about 5° C., 3.4 ml of 40% formic aldehyde were added dropwise. After stirring for 1 hour, 1.8 g of 95% sodium borohydride were added in small fractions and the mixture was stirred for 1 hour. The temperature was allowed to return to ambient and after diluting with iced water, extracting with methylene chloride, drying and evaporating to dryness under reduced pressure, filtering, washing with ether and drying, 4 g of 1,3-dihydro-7-methoxy-4-(1-methyl-3-piperidinyl)-2H-indol-2-one were obtained in the form of a base melting at ≃170° C.
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