Selective 2,3′‐Homodimerization of Indoles Using Mechanochemistry: a Convenient Synthesis 2,3′‐Biindoles

Abstract 2,3‐biindole (or 2,3‐bisindole) is an important structural feature found in many biologically active synthetic and natural products. Though many excellent methods have been reported to achieve selective 2,3′homodimerization of indole to produce 2,3‐biindole compounds, most of them need strong co‐oxidants and other additives to enable the reactions. In recent times, mechanochemistry is picking up as a promising sustainable, environmentally‐benign tool in modern organic chemistry. Because, mechanochemistry not only presents a fair deal to avoid the use of environmentally hazardous, unsafe, expensive large quantities of solvents (waste reduction), it is also found to accelerate reactions and even enable new chemical transformations. We herein report such greener, atom‐economical, solvent‐free, and oxidant‐free Pd‐catalyzed 2,3′homodimerization of two indolyl groups to furnish 2,3‐biindole compounds in an environment‐friendly fashion using Liquid Assisted Grinding (LAG) mechanochemical process.