Sequential four-component protocol for the synthesis of pyrido[1,2-a]pyrimidin-6-one derivatives in water

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

Since the beginning of this century, p-toluenesulfonic acid (p-TSA) catalysed organic transformations have been an active area of research for developing efficient synthetic methodologies. Often, catalysis using p-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, p-TSA is a non-toxic, commercially available, inexpensive solid organic compound that is soluble in water, alcohols, and other polar organic solvents. p-TSA is a strong acid compared to many protic or mineral acids and its high acidity helps activate different organic functional groups. p-TSA-promoted conversions are fast, have a high atom and pot economy, and feature a multiple bond-forming index. Therefore, the utilization of p-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 p-TSA-catalysed organic transformations, covering the literature reports that have appeared since 2012.

A versatile approach for one-pot synthesis of hybridized quinolines linked to fused N-containing heterocycles in water

Here, highly efficient one-pot protocols for the synthesis of structurally diverse fused N-containing heterocycles containing 2-chloroquinoline employing 1,1-bis(methylsulfanyl)-2-nitroethene, diamines, 2-chloroquinoline-3-carbaldehydes and dimedone/Meldrum's acid in green media in the absence of catalyst are reported. The current report proposes sustainable, simple, four-component and straightforward strategies for generating interesting N-containing heterocyclic compounds from a range of diamines and 2-chloroquinoline-3-carbaldehydes. The utilization of water as green media furnishes sustainability by preventing the usage of toxic solvent. A range of quinoline-containing aldehydes and diamines can be converted to two types of products with respect to using dimedone or Meldrum's acid via an inexpensive, one-pot and easy route.

Pyrazole-promoted synthesis of pyrrolo[3,4-c] quinoline-1,3-diones in a novel diketene-based reaction

We describe the first classic example of green synthesis of pyrrolo[3,4-c]quinolones scaffolds by catalyst-free unusual reaction of diketene, isatin, and primary amines in ethanol in the presence of pyrazole as a promoter for 4 h. The whole structure of the new product was confirmed by X-ray analysis. The overall transformation involves the cleavage and generation of multiple carbon-nitrogen and carbon-carbon bonds. This report represents a simple and straightforward approach for the synthesis of pyrrolo[3,4-c]quinoline-1,3-diones, which has significant advantages like readily available precursors, non-use of toxic solvent, operational simplicity, mild conditions, good atom economy, and excellent yields; therefore it provides a green and sustainable strategy for access to a range of interesting N-containing heterocyclic compounds in medicinal and organic chemistry.