Application of organocatalysts having dipeptide structure in asymmetric organic reactions

Asymmetric synthesis of chiral compounds have great importance in organic synthesis. Asymmetric transformations provide various ways to produce enantiomerically rich and enantiopure compounds which are widely used in pharmaceutical industry and chemical synthesis. Chiral catalysts are used to synthesize highly enantiopure compounds. Enzymes, metal and organocatalysts are the molecules which ensure obtaining chiral products with high selectivity and yield. The development of organocatalysts for asymmetric enantioselective reactions which do not contain metalic waste has great importance from the view of green chemistry. Organocatalysts are generally stable, inexpensive, easily available and non-toxic compounds. Because of their stability, they do not need harsh conditions such as inert atmosphere and dry solvent. These advantages put the enantioselective organocatalytic processes as carbon-carbon bond formation reactions into important position in organic chemistry. Aldol reaction is one of the basic reactions in carbon-carbon bond formation. Especially, the use of proline as asymmetric catalyst in these type reactions is noteworthy. Proline has some disadvantages, although, high enantioselectivity is observed in the reactions in which it is used. The low solubility of proline in most of the organic solvents affects the reactivity, moreover, some unwanted side product formations are observed, and the selectivity is low with planar aromatic aldehydes. Proline derivatives are synthesized to overcome these disadvantages. The researches on the asymmetric aldol reactions are focused on the design of new catalysts with high activity and selectivity and evaluation of their catalytic activity. Furthermore, researches on the catalytic activities in organic reactions of (S)-1,2,3,4-tetrahydroisoquinolin-3-carboxylic acid ((S)-THIQA) derivatives, which biological activities are investigated widely, are rare in the literature. In this thesis, L-Proline and (S)-THIQA based chiral organocatalysts having dipeptide structure have been designed and synthesized. The catalytic activities of these organocatalysts have been investigated on the enantioselective aldol reactions under various reaction conditions. Also, the structures of the catalysts have been determined by FTIR, 1H NMR, 13C NMR and GC-MS spectral data. As a result, positive results have been observed to show that (S)-THIQA-based organocatalysts are suitable alternatives to L-Prolin analogues which are widely used in the literature processes.