Chapter 9: Other 2-Substituted Pyrrolidines as Asymmetric Organocatalysts

Over the past decades, use of l-proline and its derived small organic molecules as catalysts for organocatalytic reactions has gained considerable attention. The replacement of the carboxylic acid functionality at the C-2 position in the pyrrolidine ring, has proven to be effective in catalysing various chemical transformations. Numerous 2-substituted pyrrolidines, such as diamines, triamines, dithioacetals, guanidines, sulfonamides, thioamides, thioureas, ureas and heterocycles (including triazoles, tetrazoles and benzothiazoles) have been studied extensively as organocatalysts. The pyrrolidine scaffold is a unique backbone for catalytic activity, which facilitates enamine and iminium ion formation and subsequent processes. The stereochemistry of the final products is generally obtained with satisfactory to excellent selectivities through covalent-bond and/or hydrogen-bonding catalysis. In this chapter we discuss the role of a wide range of 2-substituted pyrrolidine derived organocatalysts and their uses in asymmetric transformations.