Synthetic Studies Towards Ent-Kaurane Diterpenoids

In this dissertation,the synthesis of ent-kaurane diterpenoid pharicin A was investigated via the iron-catalyzed hydrogen atom transfer(HAT)reaction.ent-Kaurane diterpenoids represent an important group of natural products with diverse ring scaffolds and complex stereostructure,featuring a 6/6/6/5 tetracyclic skeleton and a unprecedented [3.2.1] bridged ring.The synthesis of ent-kaurane diterpenoids,the ironcatalyzed HAT reaction and its application in the synthesis were summarized in the introduction section.Retrosynthetically,the construction of bicyclo [3.2.1] octane was expected to be completed by aldol reaction,and the 6/6/6 tricyclic skeleton of pharicin A could be rapidly constructed through the intermolecular HAT cyclization reaction between the A-ring fragment and the C-ring fragment.With the A-ring and C-ring fragments in hand,we tried a range of reaction conditions and substrates,but failed to achieve the intermolecular cyclization.Since intermolecular reactions failed,we changed the strategy to complete the B-ring construction by intramolecular HAT cyclization.the two fragments were connected by the nucleophilic attack via the lithium-halide exchange,providing the precursor of the key HAT reaction.Subsequently,the B-ring is constructed through the intramolecular HAT reaction,and the desired transdecalin and C-9 chiral center were successfully obtained.The synthesis of 6/6/6 tricyclic skeleton of the target natural product was completed.Subsequent studies on the construction of the bicyclo [3.2.1] octane and the synthesis of natural products pharicin A are still in progress.