2-Thioether-indole compounds

Conversion of (144) to (145) has been previously shown to occur on treatment of the hexahydropyrroloindole (147) obtained by peracetic acid oxidation of tryptophan (see Section III. 1.1.). (147) is converted by 2N HCl to the oxindole (145) in dilute acetic acid (147) can also add thiols giving 2-thioether indole compounds (141) 339). 

In contrast to the 5-endo-trig anionic cyclization reactions, rarely observed, there are several examples in which 5-endo-dig processes are involved. Hence 2,3-disubstituted benzofurans, benzothiophenes and indoles 374 have been synthesized starting from triflu-oroethyl ethers, thioethers and anilines 373, respectively, and alkyllithium compounds. A 5-endo-dig carbolithiation reaction on 375, generated by two successive eliminations, one substitution and one ortho-lithiation reactions, is proposed to account for the formation of the corresponding 2-lithiated heterocycles. Further reaction of these intermediates with electrophiles affords compounds 374 (Scheme 98)159. In the case of thioether 373 (X = S) a bromine substituent must be present at the ortho position. 

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