Enantiomeric Scaffolds. Molybdenum Pyranyl π-Complexes for the Asymmetric Construction of Oxa-Heterocycles Open Access

Cheng, Bo (2008)

Permanent URL: https://etd.library.emory.edu/concern/etds/xd07gt51k?locale=en
Published

Abstract

Enantiomerically pure TpMo(CO)2(η 3-pyranyl) complexes have proven to be excellent enantiomeric organometallic scaffolds for the symmetric construction of structurally diverse oxygen-containing heterocyclic systems. Chiral, non-racemic η 3-(2,3,4)-2-methyl-5-oxopyranyl molybdenum scaffold was prepared with high enantiopurity. An improved method was developed for the synthesis of chiral, non-racemic η 3-(2,3,4)-5-oxopyranyl molybdenum scaffold.

Neutral TpMo(CO)2(η 3-pyranyl) scaffolds bearing an internal alkoxide can undergo a novel intramolecular '1,5-Michael-like' reaction. Through a one-pot '1,5-Michael-demetalation' sequence, the 6,8-dioxabicyclo[3.2.1] oct-3-en-2-one frame work can be rapidly accessed in good to excellent yields with high enantiopurity. An enantiocontrolled total synthesis of (+)-(1R,2S,5S,7R)-2-hydroxy-exo-brevicomin was completed utilizing the intramolecular '1,5-Michael-demetalation' cascade.

Solid sodium methoxide participates in an unprecedented intermolecular '1,5-Michael-like' reaction with neutral TpMo(CO)2(5-oxo-η 3-pyranyl) complexes with complete regio- and stereocontrol. The resulting dimethoxy complexes lead to the formation of various 2,2,6-trisubstituted and 2,6-trans disubstituted pyranyl molybdenum complexes. The synthetic potential of this methodology was demonstrated by the synthesis of (2S,6R)-2,6-dially-2-ethyl-2H-pyranone and (2R,6S)-2-ethyl-6-phenyl-pyranone.

Table of Contents

Chapter 1 Application of Stoichiometric Transition Metal Complexes in Organic Synthesis

Introduction
Zirconium Complexes
Chromium complexes
Molybdenum Complexes
Tungsten Complexes
Cobalt Complexes
Iron complexes
Conclusion

Chapter 2 Synthesis of 6,8-Dioxabicyclo[3.2.1]oct-3-en-2-one through a Molybdenum-mediated Intramolecular '1,5-Michael-like' Reaction

Introduction
Results and Discussion

Synthesis of Racemic and Chiral, Non-racemic 5-Oxapyranyl Scaffold 86
Mukaiyama-aldol Reaction and Aldol Reaction of 5-Oxopyranyl Scaffold 86 and 2-Methyl-5-oxopyranyl Scaffold 88
Intramolecular '1,5-Michael-like' Reaction
Intramolecular '1,5-Michael-demetalation' cascade
Total synthesis of (+)-(1R,2S,5S,7R)-2-Hydroxy-exo-Brevicomin

Conclusion
Experimental Section

Chapter 3 Synthesis of Highly Substituted Pyranones via a Molybdenum-mediated Intermolecular '1,5-Michael-like' Reaction

Introduction
Results and Discussion

Precursors for Intermolecular '1,5-Michael-like' Reaction
Intermolecular 1,5-Michael-like Reaction with NaOMe
Synthetic Application of Intermolecular '1,5-Michael-like Reaction' of NaOMe

Conclusion
Experimental Section

Chapter 4 Toward the Total Synthesis of (-)-Malyngolide

Introduction
Results and Discussion

The Synthesis of 3-Methyl-5-oxopyranyl Molybdenum Scaffold 147
Model Study toward the Synthesis of (-)-Malyngolide
Attempts to Carry out the Key Semipinacol Rearrangement

Conclusion
Experimental Section

About this thesis

Rights statement
  • Permission granted by the author to include this thesis or dissertation in this repository. All rights reserved by the author. Please contact the author for information regarding the reproduction and use of this thesis or dissertation.
School
Department
Degree
Submission
Language
  • English
Research field
Keyword
Committee Chair / Thesis Advisor
Committee Members
Last modified

Primary PDF

Supplemental Files