A new method for synthesis of 4-substituted indoles has been developed by using the 7-arylthio-6-7-dihydroindol-4(5H) one5 as a common intermediate. The method was applied to the synthesis of (S)-(−)-pindolol (11) and (±)-chuangxinmycin (16).
New, Concise Route to Indoles Bearing Oxygen or Sulfur Substituent at the 4-Position. Synthesis of (.+-.)- and (S)-(-)-Pindolol and (.+-.)-Chuangxinmycin.
A new method for the synthesis of 4-alkoxy- and 4-[alkyl (or aryl)thio]indoles has been developed by using the indolone 3 as a common intermediate. The indolone 3 was prepared from N-(phenylsulfonyl)pyrrole (7) and the α-chlorosulfide 8 in four steps. Heating of a mixture of 3 and an appropriate alcohol in the presence of p-toluenesulfonic acid and cupric chloride afforded the 4-alkoxyindoles 11a-d. The method was applied to the synthesis of (±)-pindolol (19) and (S)-(-)-pindolol (20). Thiols also reacted with 3 in the presence of boron trifluoride to give 4-[aryl (or alkyl)thio]indoles 12, 21a, b, and 22a-d. The (indol-4-ylthio)acetate 22c was employed as a key intermediate for a concise total synthesis of (±)-chuangxinmycin (27).