The design of effective organocatalyst for asymmetric organic reactions

The increasing importance of chiral molecules in pharmaceutical industry, agriculture, biology and chemistry has led to increase in the number of studies to synthesize opticaly active compounds. There are several methods for the synthesis of chiral molecules. One of them is resolution of rasemic mixtures, the second one is the synthesis of single enantiomers using chiral auxiliaries and starting materials, and the most important third one is using of chiral catalysts. The aim of all these three methods is the cheap asymmetric synthesis of highly enantiopure molecules with high yield as possible. Asymmetric catalysts can be divided into three class; these are enzymes (biological catalysts), synthetic metal complex catalysts and pure organic catalysts. Non-metal content and non-toxicity are the most important properties of organocatalysts. Besides, organocatalysts are not sensitive to oxygen and moisture, they do not require hard reaction conditions such as inert gas atmosphere and anhydrous solvent. In addition, organocatalysts are cheap, readily available and recyclable pure compounds. The Aldol reaction is one of the most important C-C bond forming reaction which allows to synthesise β-hydroxy carbonyl compounds which are the precursors of biologically active substances. Proline is the most common natural amino acid used in asymetric reactions as organic catalysts. Proline has some disadvantages, even though high enantioselectivity is observed in the reactions in which it is used. The low solubility of prolin in many organic solvents effects the reactivity, and also unwanted side product formation is observed with proline catalyst and the selectivity is low in the aldol reactions with planar aromatic aldehydes. To overcome these disadvantages, new organocatalyst derivatives have been synthesized by the modification of acid part in the L-Proline and adding new groups which can form hydrogen bond interactions. The aim of this study is the synthesis of new chiral organocatalysts with dipeptid structure based on L-Proline and investigation of their catalytic activities in asymmetric direct aldol reaction under various reaction conditions. The structures of catalysts were determined by the spectral data such as FTIR, 1H NMR, 13C NMR and LC-MS. The positive results regarding L-proline derivatives will provide an insight and contribute to the related literature.