Electroreductive Intermolecular Coupling of 3-Methoxycarbonylindoles with Ketones

The electroreductive coupling of 1-alkoxycarbonyl-3-methoxycarbonylindoles with aromatic ketones in the presence of chlorotrimethylsilane gave cis-adducts stereoselectively. The cis-adducts were readily transformed to trans-adducts by treatment with catalyst DBU. On the other hand, the electroreductive coupling of 1-methyl-3-methoxycarbonylindole with aliphatic ketones in isopropanol afforded trans-adducts exclusively. The adducts are the precursors for the synthesis of 2-substituted 3-methoxycarbonylindoles and indolines.