Synthesis of Optically Active δ-Lactones by Rearrangement Reactions

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Nowadays, the discovery of a new reaction is a very rare event in organic chemistry – and yet it has fortunately happened to us recently. This occasion is the basis for this project: In the presence of a catalytic amount of potassium cyanide 1-hydroxy-2-cyclopentanone carboxylic esters rearrange into δ-valerolactone derivatives. The latter is a prominent structural motif of natural products and synthetic compounds with relevant biological activity. In this project we would like to develop the reaction further into an enantioselective method. We are pursuing two strategies: In a first project, we are planning to control the configuration of the new stereocenter in the product by introducing an additional stereocenter into the starting material. The main and second part of this project, however, is the development of a chiral organocatalyst that allows for an enantioselective transformation to the δ-lactones. On the one hand, it is planned to use cinchona alkaloids to prepare optically active quinuclidinium cyanides and to use them as catalysts. Furthermore, we will investigate chiral ammonium salts as catalysts which are based on the trans-1,2-diaminocyclohexane scaffold. The potential of the new methodology will then be demonstrated in a third project in the stereoselective total synthesis of the natural product chebulic acid and some insect pheromones.