Studies On The Synthesis Of Melotenine A By Three-Membered Ring Expansion Stratdgy

The organic compounds with three membered rings have high reactivity due to its ring strain, thus they easily open the ring to synthesize the polyfunctional organic intermediates. Especially when three membered rings are fused to the polycyclic systems, the ring opening could lead to a ring expansion to afford some structurally complex compounds that are not readily obtained by other methods. In organic synthesis, especially in the total synthesis of some complex natural products, this kind of strategy has been used extensively. In this thesis, we aim at the construction of the crucial seven-membered aza-heterocyclodiene in Melotenine A by using the tactic of three members ring expansion of6/3bicyclic system. The main contents of this thesis are accounted for the following two parts:Part I:The cyclopropane chemistry is one of the most dynamic research areas in organic chemistry, and many reports about the structures and molecular orbitals as well as the ring opening reactions have been disclosed by chemists. So far, three types of the opening ring reactions of cyclopropanes are recorded in literature:the thermal rearrangements, the radical ring openings and Lewis acid-mediated ionic ring opening. In this chapter, we will manily review some research achievements of the opening reactions of two kinds of substituted cyclopropanes:one is gem-dihalocyclopropanes and another one is donor-acceptor cyclopropanes. In addition, we will introduce some examples of the ring expansion of cyclopropanes, which were applied in the total synthesis of natural products.Part II:Melotenine A, a unprecedented monoterpenoid-indole type alkaloids, was isolated by Chinese organic chemists in2010firstly. One of the challenges in the synthesis of Melotenine A is how to construct its novel6/5/5/6/7pentacyclic skeleton, and there is not report about its total synthesis so far. In this part, we explore the feasibility of the ring expansion reaction of cyclopropanes in the synthesis of the seven-membered aza-heterocyclodiene moiety of Melotenine A. For this purpose, some intermediates of gem-dihalocyclopropanes and ester substituted cyclopropanes were synthesized, and further investigations on the expansion of the6/3bicyclic ring systems were conducted preliminarily.