Organocatalytic Umpolung Strategies: Beyond Classical Reactivity Patterns

The organocatalytic strategies for the reversal of normal mode of reactivity (umpolung) leading to the unconventional access to the synthesis of various organic molecules have received considerable attention in the last three decades. Among the various catalysts employed for reactivity umpolung, the N-heterocyclic carbene (NHC)-based catalysts are in the forefront. NHCs are useful for the umpolung of electrophiles such as aldehydes, aldimines, Michael acceptors, and halides. In addition to NHCs, other catalysts such as metallophosphites, phosphines, and secondary amines are also employed for catalyzing transformations proceeding via umpolung. This chapter is aimed at highlighting various organocatalytic protocols for the umpolung of electrophiles, thereby shedding light on the power of these catalysts for bringing unconventional access to target molecules.