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Paper | Special issue | Vol 44, No. 1, 1997, pp.169-176
Published online, 1st January, 1970
DOI: 10.3987/COM-95-S4
Reduction of Indigo: Simple Syntheses of 3-Acetoxy-, 1-Acetyl-2,3-dihydro-, 3-Acetoxy-3'-acetyl-, 3-Acetoxy-1,3'-diacetyl-2,2'-bisindoles, and 2,2'-Bisindole

Masanori Somei,* Hiroyuki Hayashi, and Shinobu Ohmoto

*Faculty of Pharmaceutical Sciences, Kanazawa University, 13-1 Takara-machi, Kanazawa 920-0934, Japan


Indigo was converted to 2,2’-bisindole by the direct reduction with zinc in acetic acid and acetic anhydride under argon or hydrogen atmosphere. Reduction with tin and iron afforded 3-acetoxy-2,2’-bisindole predominantly. Useful building blocks such as 1-acetyl-2,3-dihydro-, 3-acetoxy-3’-acetyl-, and 3-acetoxy-1,3’-diacetyl-2,2’-bisindoles were also produced depending on metal and reaction conditions.