Cyclopropenium Ions as Organic Lewis Acid Catalysts in Reactions Involving Carbonyl Activation

Abstract

The research work presented in this thesis primarily focuses on cyclopropenium ion-catalyzed approaches to access 1,4-skipped dienes, carbocycles, heterocycles and alkyl amines derivatives. This thesis is divided into five chapters; Chapter 1 describes the general introduction to carbocations and their applications in organocatalysis. Chapter 2 describes the cyclopropenium ion catalyzed bis vinylation of aldehydes with electron-rich alkenes to access 1,4-skipped dienes. Chapter 3 involes the synthesis of 2H-chromene, quinolone, phenanthrene, and chalcone derivatives through cyclopropenium ion-catalyzed carbonyl-alkyne metathesis reaction. Chapter 4 describes the cyclopropenium ion-catalyzed direct reductive amination of aldehydes with indolines in the absence of an external hydride source. Chapter 5 portrays the synthesis of highly substituted indenone derivatives via HMPA-H2O mediated oxygenative carbocyclization of 2-alkenyl phenyl-substituted p-quinone methides. This protocol was also elaborated to the formal synthesis of one of the resveratrol based natural product called (±)-isopaucifloral F. Chapter 1: General Introduction on the Organocatalytic Applications of Carbocations. Carbocations are often considered as highly unstable and reactive species or intermediates which are thought to be non-isolable. However, in reality, it is possible to prepare some of the carbocations in a stable form and store them under ambient conditions without decomposition.