Designing Cobalt(II) Complex for Chemoselective Synthesis of 2‐Aryl‐3‐Formyl Indoles from Amino Alcohols and Alcohols†.

An air‐stable, inexpensive, and isolable cobalt(II) complex (C1) of N‐((1‐methyl‐1H‐imidazol‐2‐yl)methyl)‐2‐(phenylselanyl)ethan amine (L1) was synthesized and characterized. The complex was used to catalyze a one‐pot cascade reaction between 2‐(2‐aminophenyl)ethanols and benzyl alcohol derivatives. Interestingly, 2‐aryl‐3‐formylindole derivatives were formed instead of N‐alkylated or C‐3 alkylated indoles. A broad substrate scope can be activated using this protocol with only 5.0 mol % catalyst loading to achieve up to 87 % yield of 2‐aryl‐3‐formylindole derivatives. The mechanistic studies suggested that the reaction proceeds through tandem imine formation followed by cyclization. [ABSTRACT FROM AUTHOR]