Executive Summary : | Successful results of hydrogen bonding (HB) in the field of organocatalysis via noncovalent interactions, inspired the chemists to explore the other weak interactions for catalyzing various organic transformations. In this direction halogen bonding (XB) is becoming a growing field of research area. A noncovalent interaction between a Lewis basic center and an electrophilic halogen substituent is known as the halogen bond (XB). An XB is regarded as a soft and hydrophobic version of hydrogen bond and thus these interactions might gain countless value in the field of organocatalysis. Numerous methods have been developed to strengthen the XB, which include the preferential use of the iodine atom over the other halogens as the bonding donor, the incorporation of positive charges into the core structural motifs of XB donors, as well as the usage of various counterions which are noncoordinating in nature and also solvents. The key structural motifs of organic XB donors which have been developed so far are usually based on cationic backbones that include iodo-substituted heteroarenium salts such as iodopyridiniums, iodotriazoliums and iodoimidazoliums. The other class of XB donors are mainly based on neutral polyfluorinated and alkyne derivatives. Many from both categories have been utilized for catalyzing a diverse array of organic reactions. Besides these most potent currently available iodine(I)-based XB catalysts, hypervalent iodine(III)-derived compounds, which are also used as versatile reagents in various organic transformations is of growing attention in recent years for XB catalysis. Chemists are now become highly interested to utilize the corresponding Lewis acidity of hypervalent iodine(III) compounds as XB catalysts for important organic transformations. To date, the diaryliodonium salts have been used as a catalyst only for a few limited reactions e.g. halide abstraction reaction, Mannich reaction, and Diels–Alder reactions. Although new methods are still being in progress, there are several challenges associated with these XB catalysts which include: (I) the C−I bonds present on these catalysts being very polarized in nature, are very fragile and for this reason, the reaction conditions need to be very mild. (II) Besides this the haloarenium catalysts are decomposed very easily by light irradiation, high reaction temperature, strong nucleophiles and even the presence of a small amount of weak bases or moisture also deactivates the catalysts through decomposition. As a result, many side reactions are frequently observed. The above-mentioned undesirable side reactions will eventually result in low reaction efficacy, limited reaction type and which also lead to very poor functional group tolerance. If this problem long lasts, the applicability of XB catalysis will be greatly undermined. For avoiding the above problems instigated due to the catalyst instability, a careful design of halogen bond donor catalyst is highly awaited. |