Photoinduced Electron Transfer Processes for the Synthesis of Enantiopure Alkaloids

点击翻译按钮获取中文摘要

The diastereo- and enantioselective synthesis of representatives of the secondary plant metabolite families pyrrolizidines, indolizidines and quinolizidines by photoinduced electron transfer (PET) methods is in the focus of this german/french joint grant application. We plan to evolve optimal strategies for the design of photo- and electroactive substrates for direct PET-induced cyclizations with high regio- and diastereoselectivity by variation of the core structures for ring-annulation as well as by substituent variations. Substrates from the pool of chiral natural molecules are included in the retrosyntheses in order to achieve maximum chiral information already in the starting materials. Medium effects are planned to be studied in order to find optimal conditions for the electron transfer step as well as the subsequent C-C bond forming steps. As target molecules, polyhydroxylated pyrrolizidines are triggered from maleimides and succinimides, polyhydroxylated indolizidines additionally from pyridinium salt PET-photochemistry. On the other hand, we plan to optimize PET-sensitized processes that generate radical cations via single electron oxidation of amines by excited electron acceptors and additional radical addition to chiral alkenes. The stereochemistry of these reactions is to be entirely controlled especially as chiral centers on the amine are concerned. The variation of the structures of the amines and the acceptor olefin will be studied in order to get information on the stereoselection process and to enlarge the scope of the reaction. In several cases, the reaction conditions need to be modified to increase the reactivity (e.g. many acyclic tertiary amines are less reactive than cyclic analogues). Radical tandem reactions of unsaturated tertiary amines will be investigated in the same way. A variety of nitrogen containing heterocycles such as pyrrolizidines, indolizidines, or tetrahydroisoquinolines is available. Many of them possess interesting biological activity (e.g. as neurotransmitter analogues) and derivatives are to be tested on their activities.