Current Organic Chemistry - Volume 21, Issue 15, 2017

Background: Polyheterocyclic compounds have numerous applications in different fields ranging from medicinal chemistry to material science. Cascade reactions represent the most direct and efficient method to obtain polyheterocyclic molecules with functional diversity and increased complexity. Moreover, novel polycyclic systems can be generated which can possess interesting properties such as biological activity or luminescence. The number of polyheterocyclic compounds obtained through cascade reactions, including multi-component reactions, is wide and this review will be limited to polyheterocycles obtained from aromatic N-heterocycles: pyrrole, pyrazole, triazole, pyridine, pyrimidine, indole, benzimidazole, quinoline and other mono- or bicyclic compounds. Objective: The review will cover the period ranging from 2006 to 2015 and will focus on processes involving the formation of C-N bonds with the heterocyclic nitrogen.

Background: Cascade reactions, as an attractive branch of organic chemistry, have been the subject of intense research in the recent years. In these reactions numerous transformations occur in a single sequence, and the subsequent reactions are formed as a consequence of the functionality of the previous step. Cascade reactions are environmentally benign processes due to their one-pot procedure which accordingly proceed in a single reaction solvent, work-up, and purification step. Therefore, they are often associated with cost savings in terms of solvents, catalysts, and reagents in addition to time and effort. Objective: In the recent years, cascade reactions have been used for the construction of complicated molecular scaffolds, especially heterocyclic natural products. Different naturally occurring compounds were synthesized through cascade (tandem) reactions; this review has been focused on the use of cascade sequences for the synthesis of heterocyclic natural products.

Background: Cascade reactions are well-known as powerful process to design complex molecular structures from simple and cheap starting compounds by using two or more reactions in a single consecutive transformation. These reactions, forming a number of bonds by one operation, are useful for the creation of polycyclic and spirocyclic compounds. Thus, cascade reactions play important role in modern organic chemistry. The importance of cascade reactions are based not only on contemporary demands for more efficient and less labour-consuming methodologies for the synthesis of pharmaceuticals and other fine chemicals, but also from growing necessity to coincide the modern environmental demands. The development of electrosynthesis during last few decades have created a lot of important synthetic methodologies in the field of modern organic synthesis. Electroorganic synthesis is known as an environmentally benign methodology for many redox processes, since utilization of reagents with expressed toxicity are substituted by electric current, and the quantity of waste thus, tends to be considerably diminished. The electrochemical step is often only the first reaction in complex multi-step process, but it plays important role in producing starting reactive intermediates. Thus, organic electrochemistry offers remarkable alternatives to usual organic synthetic methods and creates a modern tool for carrying out organic synthesis. Objective: The review deals with the last trends of the application of electrochemical methods to start the assembling of heterocyclic compounds by cascade reactions.

Background: The design and performing of cascade reactions is a challenging but stimulating and interesting facet of organic synthesis, yet one that can convey conspicuous novelty, efficiency as well as elegance and sophistication to synthetic approaches. On the other hand, isocyanides are well-recognized as privileged synthons in the synthesis of a wide range of heterocycles. Objective: In this review, we try to illustrate the power, efficiency, and convenience of combining cascade process as an expedient strategy with versatility of isocyanide-based multicomponent reactions in the synthesis of aza-heterocycles from 1993 till date. Comprising isocyanides in cascade or sequential pathway also represents a milestone in combinatorial chemistry which is a bounce for this contented marriage.

Background: Heterocyclic scaffolds widely occur in natural products and pharmaceutical molecules and because of their broad biological activities, the synthesis of such frameworks with diverse approaches is one of the most attractive fields in modern organic chemistry. Recently, cascade reactions catalyzed by transition metals made astounding advances in the synthesis of heterocyclic compounds for their step economy. Among them, gold-catalyzed cascade reactions emerged as important tools to construct complicated heterocyclic architecture from simple precursors in the past decade. Objective: This review presents an overview of recent advances in gold-catalyzed cascade reactions to generate diverse heterocyclic scaffolds and its applications in total synthesis of natural products.