Study On Total Synthesis Of Euphorbia Diterpenoid (-)-Pepluanol B

This thesis stated a review on representative syntheses of the Euphorbia diterpenoids,and studied on total synthesis of the Euphorbia diterpenoid pepluanol B,resulting in its first racemic and asymmetric total synthesis.The full text contains the following three chapters:Chapter 1.Synthesis of Euphorbia and Related Diterpenoid-type Natrual Products?Review?.This chapter briefly introduces the synthesis of Euphorbia and related diterpenoid-type natural products.By presenting a large amount work of total synthesis,it exemplifies the strategies on constructing various polycyclic scaffolds of Euphorbia and related diterpenoid-type natural products.Chapter 2.Studies on Construction of Tetracyclic scaffold of Natural Product Pepluanol B and Conformational Control of the Eight-Membered-Ring.This chapter briefly introduces the isolation,structure confirmation,bioactivities of Euphorbia Diterpenoid pepluanol B.By employing the C₂-symmetric 5/5 bicyclic diol to facilitate the synthesis,a sterically hindered aldol reaction to construct the all-carbon quaternary center,a ring-closing metathesis?RCM?to forge the eight-membered ring and a stereoselective cyclopropanation to assemble the embedded cyclopropane motif,the 5/5/8/3 tetracyclic scaffold of natural product pepluanol B was successfully constructed.Subsequently we discovered the pivatol conformational issue of the eight-membered-ring system.After failure on a series of basic thermal conditions,the conformation of the eight-membered-ring was successfully inverted by introduction of a chloro-epoxide fuctionality in compound2-12.Chapter 3.Studies on Total Synthesis of Natural Product Pepluanol B.By introduction of a bromo-epoxide fuctionality in compound 2-12,the orientation of the C14 carbonyl was successfully inverted and subsequent release of the allylic alcohol moiety by Zn-Cu couple,ensued by a series of functional group transformations,we successfully completed the racemic total synthesis of natural product pepluanol B.Afterwards,the asymmetric total synthesis of?-?-pepluanol B was accomplished with 20 total steps by taking advantage of the obtained optically pure 5/5 bicyclic diol kinetically resolved by lipase.