Visible-light Photoredox Catalyzed Deprotection Of 1,3-oxathiolanes And Synthetic Studies Towards Dasyscyphin B

This thesis mainly contains two parts of work:(1)visible light photoredox catalyzed deprotection of 1,3-oxathiolanes;(2)synthetic studies towards natural diterpenoid Dasyscyphin B.It was divided into three chapters.Chapter 1.Recent applications of intramolecular aldol reaction in total synthesis of natural products(review)In this chapter,we reviewed recent applications(2007-2020)of intramolecular aldol reaction in the construction of key framework of natural products according to their classification.Chapter 2.Visible-light photoredox catalyzed deprotection of 1,3-oxathiolanesIn this chapter,we develop a new method for visible light photoredox catalyzed deprotection of 1,3-oxathiolanes using organic dye Eosin Y as photocatalyst.The deprotection procedure features the use of a metal-free catalyst,mild conditions,a broad range of substrate scope,and good functional group tolerance.Based on several mechanistic experiments and related literatures,a possible mechanism was proposed.Chapter 3.Synthetic Studies toward dasyscyphin BIn this chapter,we firstly introduced the isolation,characterization,biological activities tests and previous synthetic reports of dasyscyphins.Then we chose the most bioactive dasyscyphin B as our target.We designed and attempted three synthetic routine to construct its core skeleton.Our first synthetic route featured a key asymmetric Michael reaction to construct the quarternary full carbon stereocenter.Unfortunately,we had to abandon this routine soon due to the low chemoselectivity of Rh catalyzed carbenoid insertion reaction.Our second synthetic route featured a Nazarov reaction to construct the desired 6/6/5/6 skeleton.However,this route did not work because of the poor reactivity of Nazarov reaction.The third route featured an key intramolecular aldol cyclization to construct the 6/6/5 tricyclic motif.It successfully provided us the unique tricyclic framework which is expected to be transformed into the targeted dasyscyphin B.