The Sonogashira Coupling was proposed in the year 1975 by Nobue Hagihara, Yasuo Tohda and Kenkichi Sonogashira in their publication. This reaction is an extension to Cassar and Dieck and Heck reactions, that carries coupling with the use of palladium catalyst. But the Sonogashira reaction uses copper and palladium catalysts continuously.
It is a cross-coupling reaction is one of the most used reaction for coupling of aryl or vinyl halides and also used in organic synthesis to produce carbon – carbon bonds. It is important in wide variety of areas and has become essential in synthesis of compounds with application in material science pharmaceuticals, nanomaterials and natural product chemistry. It can be followed in a mild condition like room temperature to synthesize complex molecules.
A simple example of the sonogashira coupling reaction is tazarotene synthesizing in a treatment of acne and psoriasis, also called as Altinicline.
The mechanism of the sonogashira coupling reaction is not completely understood as it is difficult to analysing and isolating of organometallic compounds. These organometallic compounds are present in the reactions as intermediates. However, the mechanism are predicted around copper cycle and palladium cycle.
The formation of pi-alkyne complex and complex E is based on the presence of base. It makes the proton more acidic on alkyne. While, the compound F reacts with the palladium and regenerates the copper halide.