Studies On The Wagner-Meerwein Rearrangement And Synthesis Of Botryane-sesquiterpene

The thesis aims at the studies on the Wagner-Meerwein rearrangement and the synthesis of Botryane-sesquiterpene, which including two main parts:Partâ… : Investigation towards Wagner-Meerwein RearrangementWagner-Meerwein rearrangement, one of the well-known rearrangements, is prone to occur in highly strained polycyclic systems, and leads to tremendous change in their molecular structures. This character made it have lots of advantages in the synthesis of many special and complex natural products with polycyclic systems. However, the products of W-M rearrangement are usually mixtures due to the nature of the carboncations intermediates, which restrict its applications and developments.Based on the point above, this thesis disclosed a synthetically useful W-M rearrangement ofα-quaternaryβ-bromo vinyl methyl ethers. In this process, the stability of cations by introduction vinyl methyl ether group, the high migration ability of aryl group, and the thermodynamic stability ofα,β-unsaturated aldehyde directed the W-M rearrangement towards a special pathway in high yield. It afforded an excellent method not only to conquer the limitation of many competing migration pathways, but also place a aryl group atγ-position ofα,β-unsaturated aldehydes. As an application example of this WM rearrangement, n,6,6-tricyclic aromatic compounds were prepared efficiently by a tandem W-M arrangement/Friedel-Crafts alkylation, which provided a conveniently synthetic strategy to the related natural compounds.Based on the construction of n,6,6-tricyclic systems, n,7,6- tricyclic compounds were synthesized by W-M rearrangement of spirocyclicβ-bromo ketones. And many molecular frameworks of natural products with biological activities could prepared based on this process, for the most example : (±)-Colchicine.Partâ…¡: Synthetic studies on the botryane-sesquiterpene Botryane is a kind of novel sesquiterpenes, which is isolated from the metabolites plant pathogens Botrytis. During the course of synthetic studies on them, this thesis constructed the general subunit-the sterically hindered cyclopenta--ketone with a quaternary carbon conveniently and efficiently, the key step was based on a semipinacol rearrangement process of a-hydroxyl epoxides. Among this kind of sesquiterpenes, botrydial is the most representative one with six continuous chiral centers, its other sterically hindered ring with multi-stereocenter was expected to be synthesized based on the inter- and intra-molecular aldol reaction, tandem inter-molecular Reformatsky and carbonyl-alkene reductive coupling, Barbier, intra-molecular Reformatsky reactions promoted by SmI₂, and also the intermolecular D-A reaction. Although it has not been completed after persistent endeavor up to now, all those investigations below have afforded valuable information for the first asymmetric synthesis of botryane-sesquiterpene.