Novel Tartaric Acid Derived Asymmetric Organocatalysts

The ability to control the three-dimensional structure of the molecular architecture is one of the primary targets in synthetic organic chemistry. Amongst the various ways of creating enantiomerically enriched products, catalytic methods are considered to be the most appealing as the use of stoichiometric amounts of valuable chiral reagents can be avoided, thus making optimum use of the chiral pool. Besides enzymatic and metal catalyzed asymmetric transformations, the use of sub-stoichiometric amounts of organic molecules (so called organocatalysts) has proven to possess an enormous potential for the catalysis of stereoselective reactions. Among the easily available natural chiral sources, tartaric acid has obtained a prominent position not only for historical reasons, but especially due to the fact that both enantiomers are readily available from natural sources. Surprisingly, although tartaric acid derivatives are almost omnipresent in metal catalysis, their use as chiral organocatalysts has so far been limited to a few applications only. Due to the fact that tartaric acid represents a very unique carbon skeleton possessing electronic and steric properties different from other commonly used chiral moieties the primary target of this project is the synthesis of novel tartaric acid derived organocatalysts and their application in asymmetric catalysis. As both, L- and D-tartaric acid are easily and cheaply available, access to both enantiomers of new catalysts is guaranteed. Among the different activation modes, which are hitherto known in organocatalysis, the main focus herein lies on the synthesis of chiral ammonium salts, chiral Lewis acids/bases, and bifunctional catalysts. These compounds should enable the catalysis of a wide variety of different fundamental reactions. Therefore, in each case the ability of the new catalysts for the asymmetric catalysis of reactions like alkylations, allylations, aldol type reactions, or cyclizations will be investigated. Furthermore, a careful investigation concerning the crucial structural parameters of the novel catalysts will be undertaken. The development of these novel organocatalysts will broaden the scope of organocatalysis as it will make use of one of the most easily available and cheapest natural chiral sources which has so far not been exploited much in this field. Furthermore, due to the characteristic and unique structural features of these catalysts, different reactivities compared to the currently used organocatalysts seem to be possible.

The ability to control the three-dimensional structure of the molecular architecture is one of the primary targets in chemistry. Amongst the various ways of accessing chiral compounds catalytic methods are considered to be the most appealing. Thus, the development of novel powerful catalysts is an important task. Among the easily available natural chiral sources, tartaric acid has obtained a prominent position, especially due to the fact that both enantiomers are readily available. Surprisingly, although tartaric acid derivatives are almost omnipresent in metal catalysis, their use as chiral organocatalysts (small molecule organic catalysts) has so far been limited to a few applications only. Due to the fact that tartaric acid represents a very unique carbon skeleton possessing electronic and steric properties different from other commonly used chiral moieties the primary target of this project was the synthesis of novel tartaric acid derived organocatalysts and their application in asymmetric catalysis. In the course of this project we succeeded in introducing two novel promising classes of asymmetric organocatalysts as well as new methods for the syntheses of important organic target molecules. More specific, a new family of promising chiral spiro-ammonium salt catalysts and a new generalized approach to access a so far not accessible class of very interesting chiral bifunctional ammonium salts were developed. In addition we reported the first ammonium ylide-based protocol for the high-yielding synthesis of amide-based epoxides. This result also laid the basis for a new recently granted FWF project (P 26387 Syntheses of (chiral) hetero- and carbocycles using ammonium enolates).