-Toluenesulfonic acid-promoted organic transformations for the generation of molecular complexity.

Since the beginning of this century, -toluenesulfonic acid (-TSA) catalysed organic transformations have been an active area of research for developing efficient synthetic methodologies. Often, catalysis using -TSA is associated with many advantages, such as operational simplicity, high selectivity, excellent yields, and ease of product isolation, which make organic synthesis convenient and versatile. Notably, -TSA is a non-toxic, commercially available, inexpensive solid organic compound that is soluble in water, alcohols, and other polar organic solvents. -TSA is a strong acid compared to many protic or mineral acids and its high acidity helps activate different organic functional groups. -TSA-promoted conversions are fast, have a high atom and pot economy, and feature a multiple bond-forming index. Therefore, the utilization of -TSA enables the synthesis of many important structural scaffolds without any hazardous metals, making it desirable in numerous applications of sustainable and green chemistry. Recently, this emerging area of research has become one of the pillars of synthetic organic chemistry to synthesise biologically relevant, complex carbocycles and heterocycles. This study provides a comprehensive summary of methods, applications, and mechanistic insights into -TSA-catalysed organic transformations, covering the literature reports that have appeared since 2012.