6-chloro-spirocyclohexenindol-2-ones: An unusual ring transformation to ethyl 2-(cyclohexa-1,4-dienyl)phenylcarbamates

The Diels-Alder cycloaddition reaction of 3-chloromethylen-2-indolones 1 with a series of dienes 2 was studied in order to synthesize spirocyclohexenindolones 3 and 4. The reaction proceeded with good diastereoselectivity and regioselectivity. Chlorospirocyclohexenindolones 3 and 4 were transformed into 2-aminobiphenyl derivatives 5 by reacting with sodium ethoxide. Starting from the indolone 1c and 2,3-dimethylbutadiane the spiro compounds 3 f and 4e were obtained. On treatment with sodium ethoxide, 3f was transformed into the phenanthridone derivatives 7 and 8.