Organometallic Scaffolding as a Practical Approach toDiversity-Oriented Synthesis: Stereo- and RegiocontrolledSequential Functionalization of Pyranylalkylidene AllylmolybdenumComplexes Público
Lee IV, Maurice duPont (2008)
Abstract
Organometallic enantiomeric scaffolding is a powerful and versatile tool for enantiocontrolled bond construction. Tp(CO)2allylmolybdenum complexes of pyrans and piperidines are noteworthy examples of this approach to synthesis. A streamlined procedure for the construction of the key h3(2,3,4)-5-oxopyranyl molybdenum complex was developed, facilitating scale up, and making these scaffolds more available to the synthetic community. The key scaffold was derivatized to include an alkylidene moiety that provided new opportunities for synthesis of heterocyclic skeletons and stereochemical relationships not accessible with existing methods. An unprecedented intermolecular 1,5-Michael reaction of this substrate was evaluated for its scope and mechanism, whereby the addition of alkoxide nucleophiles to neutral allyl molybdenum complexes is apparently favorable, and likely goes through an anionic molybdenum intermediate. The products of this reaction were studied for use in a novel and general sequential functionalization protocol, whereby iterative leaving group abstraction/nucleophilic addition sequences afford highly substituted pyran architectures with divergent, yet predictable regiochemical outcomes, notably those bearing 2,6-trans and 2,2,6- functionality. Other highlights include a [5+2] cycloaddition reaction to 5,6-disubstituted pyranyl complexes, and hetero Diels-Alder reaction to form spiroketals. The full utility of the method is ultimately demonstrated by the synthesis of highly functionalized enantiomerically pure pyran rings bearing functionality equipped for further manipulations.
Table of Contents
Chapter 1: Highlights of recent developments in the synthesis of 2,6-cis and 2,6-trans substituted pyrans. Introduction to organometallic scaffolding as a means of generating highly functionalized pyran architectures
Introduction:
Reductions of Hemiketals
Hetero Diels-Alder Cycloadditions
Metal-Catalyzed Cycloetherification Reactions
Ring Opening/Cyclization onto Epoxides
Prins Cyclizations and Related Reactions
Enantiomeric Scaffolding Approach to Stereocontrolled Synthesis
Results and Discussion:
Improved Synthetic routes to 5-oxopyranyl scaffold
Conclusions:
Experimental Details:
Chapter 2: Efforts toward the synthesis of non-anomeric spiroketals using pyranylalkylidene η3-allylmolybdenum complexes
Introduction:
Spiroketals and the Anomeric Effect
Synthesis of Non-Anomeric Spiroketals
Project Design
Improved Synthetic Routes to Enone Complexes
Hetero Diels-Alder Cycloadditions
Attempts to Functionalize the 2-Position of Spiroketal Complex
Conclusions:
Experimental Procedures:
Chapter 3: The intermolecular 1,5-Michael Reaction: Mechanistic studies, and efforts toward its application to spiroketal synthesis
Introduction:
Results and Discussion:
Investigating the Scope of the Intermolecular 1,5-Michael Reaction
Synthetic Applications of the Intermolecular 1,5-Michael Reaction
Rationalizing the Ionization Selectivity
Conclusions:
Experimental Details:
Chapter 4: A highly regio- and stereoselective ionization/nucleophilic addition
sequence leading to the construction of functionalized pyrans bearing stereochemical,
substituent and skeletal diversity
Introduction:
Results and Discussion:
Investigation into INA reaction of 78
Synthetic Elaboration if INA Products to Diverse and Highly Functionalized Pyrans
Second INA Sequence to Provide Trifunctionalized Pyrans
Synthetic Elaboration and Demetalation of Products
Stereo- and Regiocontrolled Synhtesis of Functionalized Pyrans of High Enantiopurity
Conclusions:
Experimental Details:
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Organometallic Scaffolding as a Practical Approach toDiversity-Oriented Synthesis: Stereo- and RegiocontrolledSequential Functionalization of Pyranylalkylidene AllylmolybdenumComplexes () | 2018-08-28 12:14:34 -0400 |
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