Recent advancements in the Ullmann homocoupling reaction for the synthesis of biaryl compounds

In the realm of biaryl synthesis, the Ullmann homocoupling reaction is a fundamental process for constructing biaryl compounds and has historically been driven by copper catalysis. However, significant studies have been made in Ullmann-type coupling reactions, particularly in the formation of biaryl structures, leading to more sustainable and efficient synthetic pathways. Recent research has concentrated on devising innovative catalytic systems, including palladium, gold, and nickel nanoparticles, and bimetallic species, to surmount the limitations of conventional copper catalysts. These advancements have broadened the range of substrates and enhanced reaction efficiency under gentler conditions, in line with the principles of green chemistry. Mechanistic studies have been instrumental in these developments, particularly focusing on the nonchain single-electron transfer (SET) mechanism. Additionally, the use of recyclable heterogeneous catalysts has mitigated the stringent reaction conditions associated with the original Ullmann reaction. As research continues to evolve, asymmetric Ullmann coupling is anticipated to become a key tool in the synthesis of complex natural products and heterocyclic systems pertinent to medicinal chemistry. This review aims to cover the recent developments in the Ullmann homocoupling reaction in sustainable and asymmetric catalytic systems for the synthesis of biaryl compounds.