Studies On The Total Syntheses Of Walsucochin B And Lycospidine A

This dissertation is mainly focused on the total synthetic studies of Nortriterpenoid Walsucochin B,Bisnorditerpene rel-(5β,8α,10α)-8-hydroxy-13-methylpodocarpa-9(11),13-diene-3,12-dione and Lycopodium alkaloid Lycospidine A.It consists of the following four chapters: Chapter 1 Applications of Cationic Domino Reactions in Organic Syntheses(review)Cationic domino reactions could be used to synthesize multiple stereocenters or multiple ring systems in one step.The reactions are environment-friendly and atomeconomic,inherently with high chemoselectivity,regioselectivity,stereoselectivity,and entioselectivity.Based on these advantages,cationic domino reactions received extensive attention and application.In this chapter,applications of cationic domino reactions in organic syntheses were briefly summarized.Chapter 2 Studties on the Total Synthesis of Nortriterpenoid(–)-Walsucochin B.In this chapter,Nortriterpenoid(–)-Walsucochin B was introduced including isolation,structure,and potential biological properties.A convergent strategy was used to obtain the cyclization precursor,starting from commercially available 2,3-dimethylanisole.The cationic polyolefin cyclization was employed to construct the core architecture as a single diastereoisomer with [6,5,6,6] fused tetracycle,four contiguous stereocenters,including two quaternary carbon stereocenters in one step under the condition of Lewis acid.Also late-stage site-selective free-radical halogenation and oxidation was utilized to accomplish the site-selective oxidation of the two methyl group on the aromatic ring.And a Seyferth-Gilbert homologation was adopted to install the acetylene moiety to construct the phenylacetylene.We have accomplished the first enantioselective total synthesis of(–)-walsucochin B and confirmed its absolute configuration.Chapter 3 Studties on the Total Synthesis of Bisnorditerpene(+)-(5β,8α,10α)-8-hydroxy-13-methylpodocarpa-9(11),13-diene-3,12-dioneIn this chapter,Bisnorditerpene(+)-(5β,8α,10α)-8-hydroxy-13-methylpodocarpa-9(11),13-diene-3,12-dione was introduced including isolation,structure,and potential biological properties.A Corey–Seebach umpolung reaction was used to synthesize the cyclization precursor,starting from a known aldehyde.A cationic domino cyclization was employed to construct [6,6,6] fused framework,and three stereocenters(two of which are quaternary stereocenters)in one step.And an oxidative dearomatization reaction was utilized to form 1,4-quinoid moiety.We have accomplished the first enantiselective total synthesis of this bisnorditerpene by 7 steps in 18.5% overall yield.Chapter 4 Studties on the Total Synthesis of Lycospidine A.In this chapter,Lycopodium alkaloid Lycospidine A was introduced including isolation,structure,and potential biological properties.And the key precusor was prepared via Michael-type addition,staring from known sulfoxide.The key intramolecular amidation/aza-Prins cyclization was used to construct the [6,6,6] fused tricylclic.An intramoleculr aldol condensation was utilized to achieve [5,6,6,6] fused tetracylic skeleton of Lycospidine A.