Transition-Metal-Free Synthetic Strategies for the Cross-Coupling Reactions in Water: A Green Approach

A natural driving force is always working behind the synthetic organic chemists towards developing ‘green’ synthetic methodologies for the synthesis of useful classes of organic molecules having potential applications. The majority of the essential classes of organic transformations, including C-C and C-X (X = heteroatom) bond-forming cross-coupling reactions, and cross dehydrogenative- coupling (CDC) mostly rely on the requirement of transition-metal catalysts and hazardous organic solvents. Hence, the scope of developing green synthetic strategies by avoiding the use of transition-metal catalysts and hazardous organic solvents for these important and useful classes of organic transformations is very high. Consequently, several attempts have been made so far. Water is the most abundant, cheap, and green solvent globally. Therefore, numerous synthetic methods have been developed in an aqueous medium. In this review, the development of transition-metalfree green synthetic strategies for various important classes of organic transformations such as C-C and C-X bond-forming cross-coupling, cross dehydrogenative-coupling, and oxidative-coupling in an aqueous media is discussed.