Polarized ketene S,S- and S,N-acetals. Part 52. Lead tetra-acetate oxidation of 3-anilino-3-methylthio-2-arylacrylonitriles. A novel approach to substituted indoles
Abstract
Lead tetra-acetate oxidation of 3-anilino-3-methylthio-2-phenylacrylonitrile (4a) gave the iminoacetate (5a) and 3-cyano-2-methylthio-1-phenylindole (6a). The corresponding methoxy substituted 2-arylacrylonitriles (4b–d), however, yielded the symmetric dimeric products (7a–c) and the unstable iminoacetates (5a–d) respectively under similar conditions. The corresponding p-chloro derivative (4e) afforded the stable iminoacetate (5e), dimer (7d), and 6-chloroindole (6e) in low yields. The iminoacetates (5a–e) could be cyclized to the respective indoles (6a–e) in the presence of boron trifluoride–diethyl ether. The probable mechanistic pathways for the formation of various products are described.