Indium‐catalyzed reductive coupling of aromatic carbonyl compounds and imines in the presence of aluminum and chlorosilanes

Abstract

AbstractReductive homocoupling of aromatic aldehydes, ketones, and imines has been achieved in tetrahydrofuran (THF) at room temperature using a catalytic amount of InCl3 (0.5–3.0 mol %) under a nitrogen atmosphere in the presence of chlorotrimethylsilane (TMSCl) and aluminum metal (Al) to provide the corresponding 1,2‐diols and 1,2‐diamines, respectively, in good to moderate yields. Other indium compounds such as In(NO3)3, cyclopentadienylindium, and indium metal have also been revealed to be effective as catalysts. The catalytic effect of the indium compound is remarkable, and, thus, without it, no reaction occurs in the case of aromatic aldehydes and aldimines, and an induction period is quite long in the case of aromatic ketones. Without either TMSCl or Al, no reaction proceeds even in the presence of the catalyst. Unfortunately, the diastereoselectivity of the products (dl and meso) is not high. Although the precise reaction scheme is not yet clear, we tentatively propose that a redox‐active In‐Al alloy might be formed on the surface of aluminum in the presence of TMSCl, and an electron transfer from the alloy to substrate might occur. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:309–316, 2001