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.