The reaction of 1-aminoindolin-2-one (I) with phenylacetone (A) by means of acetic acid in refluxing ethanol gives 1-(alpha-methylphenethylidiene-imino)indolin-2-one (II), which by reaction with refluxing ethanolic hydrogen chloride affords ethyl alpha-(2-methyl-3-phenylindol-7-yl)acetate (III). The ozonolysis of (III) in acetic acid yields ethyl 2-acetamido-3-benzoylphenyl-acetate (IV), which is cyclized by refluxing with HCl in acetic acid to give 7-benzoylindolin-2-one (V). Finally, of the ester (III) with KOH in refluxing water affords the corresponding acid (this compound is hydrolyzed with NaOH in refluxing water). The hydrolysis of the ester (III) with KOH in refluxing water affords the corresponding acid (VI), which can be ozonolyzed as before yielding 2-acetamido-3-benzoylphenylacetic acid (VII). This acid can be cyclized to (V) by refluxing with HCl in acetic acid as before.

The reaction of 1-aminoindolin-2-one (I) with phenylacetone (A) by means of acetic acid in refluxing ethanol gives 1-(alpha-methylphenethylidiene-imino)indolin-2-one (II), which by reaction with refluxing ethanolic hydrogen chloride affords ethyl alpha-(2-methyl-3-phenylindol-7-yl)acetate (III). The ozonolysis of (III) in acetic acid yields ethyl 2-acetamido-3-benzoylphenyl-acetate (IV), which is cyclized by refluxing with HCl in acetic acid to give 7-benzoylindolin-2-one (V). Finally, of the ester (III) with KOH in refluxing water affords the corresponding acid (this compound is hydrolyzed with NaOH in refluxing water). The hydrolysis of the ester (III) with KOH in refluxing water affords the corresponding acid (VI), which can be ozonolyzed as before yielding 2-acetamido-3-benzoylphenylacetic acid (VII). This acid can be cyclized to (V) by refluxing with HCl in acetic acid as before.