Studies On Synthesis Of Mycorrhizins And The Prins Cyclization Via C-H Activation

This thesis main focused on the synthetic research of Mycorrhizin A and its analogues. An efficient 3-exo cascade reaction has been developed for the synthesis of angularly fused 6,3,5-tricyclic skeleton. Meanwhile, A novel Prins cyclization through benzylic/allylic C-H activation are also studied. It consisted of the following three parts:Chapter 1. The development of cascade reactions induced by carbocation. (review)The recent development of cascade reactions induced by carbocation and application in natural products syntheses were briefly reviewed.Chapter 2. Synthetic studies toward Mycorrhizin A and its analogues.The bioactivity and synthetic background of Mycorrhizins were introduced briefly. The angularly fused 6,3,5-tricyclic system is readily generated via a 3-exo cascade cyclization under acid promotion. The reaction proceeds at room temperature with high stereochemical fidelity from the electrophilic center of the epoxide to the cyclopropane product. This methodology provides a potentially useful approach for the synthesis of mycorrhizin A and its analogues.Chapter 3. A novel Prins cyclization through benzylic/allylic C-H activationThe Prins cyclization and methodologies based on DDQ oxidation were reviewed in briefly. A step-economic method to construct tetrahydropyran ring, involving sequential benzylic/allylic C-H bond activation via DDQ oxidation and nucleophilic attack of an unactivated olefin, is described. The equatorial-trisubstituted Prins products are obtained from benzyl-and allyl-homoallylic ethers with high yield and stereochemical fidelity.