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Development of tandem synthesis of heterocycles

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Title
Development of tandem synthesis of heterocycles
Author
Choi, Subin
Advisor
Park, Cheol-Min
Issue Date
2020-08
Publisher
Graduate School of UNIST
Abstract
C-C and C-N bond formation in organic synthesis is a very important process. Whereas, small pieces are paired to form large units in intermolecular reaction, complex molecules are formed by cyclization in intramolecular reactions. The subject of modern organic synthesis is to improve efficiency, exclude toxic reagents, control pollutants and utilize resources efficiently. One way to achieve this goal is the development and application of the tandem reaction. The tandem reaction consists of several bond-forming reactions and can cause two or more transformations in one pot reaction. The tandem reaction is an economically and ecologically advantageous synthetic method capable of high efficiency synthesis of structurally complex molecules from simple substrates. This thesis deals with research on the synthesis of carbazole, dihydro[4,3-b]indolopyran and 2,3-dihydrofurans synthesis methods in tandem reaction. In chapter 1, we have developed viable reaction conditions that allow the synthesis of carbazoles in a three-step one-pot sequence. Our strategy involves tandem gold-copper catalysis in which respective catalysts work in sequence to activate respective functionalities leading to the formation of carbazoles without isolation of intermediates. The optimization process for reaction conditions and the substrate scope will be discussed in this chapter. In chapter 2, the synthesis of dihydropyrano[4,3-b]indoles and 2,3-dihydrofurans based on direct C-C radical-radical cross-coupling under transition-metal-free conditions is described. This iodine-mediated oxidative coupling features extremely mild conditions and fast reaction kinetics. A distinct reaction mechanism involving charge­accelerated SET (single electron transfer) between coupling partners followed by cage­collapse allows highly efficient cross­coupling despite the use of equimolar amounts of coupling partners. These unusual characteristics prompted us to examine the underlying mechanism of the reaction in depth. In chapter 3, Oxidative [3+3] cycloaddition based on electrolysis offer an efficient route for dihydropyrano[4,3-b]indoles and 2,3-dihydrofurans. In this approach, respectively reactive intermediates formed after radical-radical cross-coupling of indoles/enamines with active methylene compounds undergoes cyclization to produce a final product in a tandem reaction. The synthetic pathway is especially notable by taking advantage of chemistry occurring at both the anode and the cathode. The HAT-mediated cross-coupling was supported by extensive mechanistic studies, and some of the applications are shown in chapter 3.
Description
Department of Chemistry
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