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Communication | Special issue | Vol 5, No. 1, 1976, pp.233-238
Published online, 1st January, 1970
DOI: 10.3987/S-1976-01-0233
Rections and Synthetic Applications of β-Ketosulfoxides. VII. A Novel Synthesis of Pyranocarbazole Alkaloids, Girinimbine and Murrayacine

Yuji Oikawa* and Osamu Yonemitsu

*Faculty of Pharmaceutical Sciences, Hokkaido University, Kita 12 Nishi 6, Kita-ku, Sapporo, Hokkaido 060-0812, Japan

Abstract

On treatment with p-toluenesulfonic acid in acetonitrile, 1-(3-indolylmethyl)ethyl-4-methyl-1-methylsulfinyl-3-pentenyl ketone (6a) prepared from methyl indoleisobutyrate (8) with sodium methylsulfinylmethide followed by prenylation gave dihydrogirinimbine (7) through three consecutive acid-catalyzed reactions. Compound (7) was converted into N-phenylsulfonamide (11), which was dehydrogenated with N-bromosuccinimide in the presence of azobisisobutyronitrile to afford N-phenylsulfonylgirinimbine (12). Lithium aluminium hydride reduction of 12 gave girinimbine (4). Oxidation of 4 with DDQ furnished murrayacine (5). Under similar conditions, 7 gave cycloheptaphylline (13). The results in this communication may provide a shortcut and convenient method for the synthesis of pyranocarbazole alkaloids.