Organometallic Enantiomeric Scaffolds in the Synthesis of Alkaloids: I. Homo-SN2'-like Reaction/Annulative Demetallation and the Application in the Synthesis of (+)-Isofebrifugine II. Uncatalyzed Electrophilic Carbon-Carbon Bond Forming Reactions of Pyranyl and Pyridinyl Molybdenum Complexes.

摘要

Chapter One A novel homo-SN2'-like reaction between neutral TpMo(CO)2(5-acyloxy-η3-pyranyl) and TpMo(CO)2(5-acyloxy-η3-pyridinyl) scaffolds and a variety of stabilized carbonanion nucleophiles provided a powerful methodology to construct C-C bonds stereoselectively. Moreover, it proceeded through an interesting anionic mechanism and preliminary mechanistic study was reported. Based on the Mo complex produced in the reaction, a mechanistically related annulative demetallation was developed to furnish the framework of 2,7-dioxabicyclo[4.3.0]nonane and 2-aza-7-oxabicyclo[4.3.0]nonane in good to excellent yields. In order to demonstrate the power of this new reaction sequence, (+)-isofebrifugine was synthesized in a concise route by employing the homo-SN2'-like-annulative demetallation sequence.;Chapter Two Neutral TpMo(CO)2(5-trifluoroacetate-η 3-pyranyl) and TpMo(CO)2(5-trifluoroacetate-η 3-pyridinyl) scaffolds underwent an uncatalyzed Friedel-Crafts-like reaction with a variety of electron-rich arenes and olefins to form substitution products in high yields. A preliminary study of the mechanism showed that TpMo(CO)2(5-trifluoroacetate-η3-pyranyl) in DMSO rapidly rearranged to TpMo(CO)2(2-trifluoroacetate-η 3-pyranyl) complex first, which then reacted with indole derivatives. By contrast, TpMo(CO)2(5-trifluoroacetate-η3-pyranyl) in acetonitrile or chloroform reacted with electron-rich arenes and olefins without the initial rearrangement. And, silyl enol ethers and allylsilanes could only react with the unrearranged TpMo(CO)2(5- trifluoroacetate-η 3-pyranyl) complex. Further annulative demetallation proved to be successful with a series of substrates to form oxygen heterocycles and carbocycles in 5 or 6 membered rings in a mild condition. This methodology has been successfully utilized to access the tetracyclic structure of vindoline in a model system.;Chapter Three A short, practical route to a versatile 5-oxo-4-methyl-(η-2,3,4)- allylmolybdenum pyranyl and 5-oxo-4-methyl-(η-2,3,4)-allylmolybdenum pyridinyl scaffold has been developed using the Achmatowicz rearrangement. Further transformation through reduction and dehydration enabled a rapid access to Δ5-4-methyl-(η-2,3,4)-allylmolybdenum pyridinyl scaffold.