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


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

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

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

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

Experimental Section

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

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

Experimental Section

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

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

Experimental Section

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