Group 13 sulfides indole derivatives

Indok synthesis. Gassman and van Bergen have used a modification of the above-mentioned procedure for synthesis of 2-substituted indoles from anilines. The aniline IS treated as above with a chlorinating reagent at — 65° and then an equivalent of methyl-thio-2-propanone at the same temperature. An equivalent of a base (usually triethyl-amine) is added. Workup affords the indole derivative (2) in 60-70% yield. The thio-methyl group is removed with Raney nickel (>70% yield). The keto sulfide can be varied thus nse of methyl phenacyl sulfide [CH3SCH2C(=0)C5H5]4 in the synthesis leads to 2-phenylindoles. 

The above reaction sequence (Scheme 11), sometimes called the Katritzky method, has been exploited by a number of research groups for the preparation of 2-substituted IV-unsubstituted indoles [83, 102, 130, 218, 240-245], Gribble and Bergman used this chemistry to prepare 2-bromoindole and 2-iodoindole [246-248]. Bergman and Janosik further explored this sequence to prepare indol-2-yl sulfides and selenides [57,249,250]. Hudkins has used this chemistry to prepare 2-hydroxyatkylindoles en route to indolocarbazole derivatives [251, 252], The first step in Bergman s short total synthesis of yuehchukene used the Katritzky method and aldehyde 59, which gave 2-(hydroxyalkyl)indole 60 (Scheme 12) [253, 254]. 

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