Research On The Total Synthesis Of Natural Products Of Cephalotane-type Cephalotaxus For Reducing Carbon Diterpenoids

In this paper,palladium-catalyzed cascade reactions were reviewed and the total synthesis of Cephalotane-type norditerpenoids isolated from cephalotaxus have been studied.The main contents include the following two chapters:Chapter 1:Application of Pd-cascade Reactions in Total SynthesisIn this chapter,we divided the palladium-catalyzed cascade reactions into five categories:(1)palladium-catalyzed coupling-type cascade reactions;(2)cascade coupling between palladium-catalyzed coupling reactions and redox reactions;(3)palladium-catalyzed reduction cascade reactions;(4)palladium-catalyzed cascade reactions involving the insertion of other components;(5)other types of palladium-catalyzed cascade reactions.Moreover,we reviewed the application of palladium-catalyzed cascade reactions in total syntheses of natural products.A number of examples of palladium-catalyzed cascade reactions in the synthesis of natural products were documented,and the role of palladium-catalyzed cascade reactions in these synthetic studies was described.Chapter 2:Total Synthesis of Cephalotane-Type NorditerpenoidsThis chapter first introduced the isolation,structure identification and research background of 28 natural products of cephalotaxus.The total synthesis of Harringtonolide has been briefly described.Secondly,we focused on the total synthesis of Cephalotane-type norditerpenoids.Cephalotane-type norditerpenoids contain an aromatic ring,a fused 5/6/6 cis-tricyclic system and a cage-type structure,as well as a lactone bridged bicyclic ring system.Based on the above structural characteristics,we designed a palladium-catalyzed intramolecular cascade carbonylation reaction to construct a 6/5/6/6 tetracyclic system.Since the ketone type substrate that was originally designed is difficult to cyclize,we changed the strategy to use the bridged ring structure to complete the reaction.However,the steric hindrance of the bridged lactone unit leads to poor stereoselectivity.We have tried the acetal type substrate,and finally successfully completed the stereoselective cascade reaction,and further completed the synthesis of Cephanolides B and C.For the synthesis of Cephanolide A,we have not yet constructed a five-member ether ring,but further studies are still in progress.