Total Syntheses Of Isospongian Diterpenoids Kravanhins A-C And Synthetic Studies Toward Lycopodium Alkaloid Annotinolide B

The thesis describes recent advances of olefin [2+2] photocycloaddition reactions and efforts toward total syntheses of isospongian diterpenoids kravanhins A-C and Lycopodium alkaloid annotinolide B.Chapter 1.Olefin [2+2] Photocycloaddition Reactions(Review)The review aims to discuss advances in the synthesis of cyclobutanes by olefin [2+2] photocycloaddition reactions which occur by direct excitation or sensitization in the last 20 years.According to the photochemically excited olefin,nonconjugated alkenes,arene-conjugated alkenes,?,?-unsaturated ketones,and ?,?-unsaturated carboxylic acid derivatives were discussed in individual subsections.Chapter 2.Total Syntheses of Isospongian Diterpenoids Kravanhins A-CA brief introduction of the background for the isolation and syntheses of spongian diterpenoids is provided.Theree novel tetracyclic isospongian diterpenoids kravanhins A-C represent attractive targets for our group.In the first study,we report the first asymmetric total synthesis of(-)-kravanhin B(13 steps,6.2% overall yield).The synthesis features an intramolecular aldol cyclization to construct the desired trans-anti-cis fused tricyclic ring skeleton and an acid catalyzed dehydration and olefin isomerization to install the ?-butenolide ring.In the second study,we report the first asymmetric bioinspired total syntheses of kravanhins A and C.We proposed a plausible biosynthetic pathway for isospongian diterpenoids from labdane diterpenes,and then retrosynthetic analysis toward(-)-kravanhins A and C was described.A convergent pathway was used to construct the furanolabdane derivative,followed by a photooxidation with singlet oxygen gave the required ?-hydroxybutenolide labdane derivative.Then(-)-kravanhin C was obtained through a one-pot sequential aldol cyclization and lactonization.At last stage,the synthesis of(-)-kravanhin A was completing via a regioselective and stereoselective reduction.This work is worthy for searching biosynthetic pathway for terpenoids.Chapter 3.Synthetic Studies toward Lycopodium Alkaloid Annotinolide BA brief introduction of the isolation and representative syntheses of Lycopodium alkaloid lycopodine is provided.The novel Lycopodium alkaloid annotinolide B represents attractive target for our group.The retrosynthetic analysis features an aldol condensation to construct A-ring and an olefin [2+2] photocycloaddition reaction to construct cyclobutane ring and lactone ring.At present,an intramolecular aldol condensation has been used to construct the desired ABC tricyclic ring skeleton.This synthetic study is ongoing.