New entry to 1,4,5,6-tetrahydro-2h-indol-2-ones using a cationic 5-endo-trigonal cyclization onto enamides

Article abstract of DOI:10.3987/COM-97-S8

A new method for the synthesis of 1,4,5,6-tetrahydro-2H-indol-2-ones by means of 5-endo-trigonal cyclization of α-thiocarbocations generated from sulfoxide (12) and α-chlorosulfide (17) is described. The sulfoxide (12), upon heating with TsOH, gave 14, which eliminated benzenethiol to give tetrahydroindolone (15). By contrast, the chlorosulfide (17), upon treatment with TiCl₄, gave the desulfurized tetrahydroindolone (18). The mechanism for the formation of 18 is also discussed.