Intramolecular Diels-Alder and Alder Ene Reactions (Reactivity and Structure: Concepts in Organic Chemistry 18)
By: Douglass F. Taber (author)Hardback
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The Diels-Alder reaction has long been a powerful tool in organic synthesis. In recent years, the Alder ene reaction has also achieved some prominence. From the beginning, it was apparent that the intramolecular variants of these reactions would be feasible. Many such have been reported, but the results are widely scattered in the chemical literature. This volume is an attempt to synthesize results observed to date, and to suggest directions for future development. One of the limiting factors in the application of the intramolecular Diels- Alder reaction has been the development of methods for the preparation of the requisite trienes. The fIrst chapter of this volume summarizes methods for the preparation of dienes and dienophiles. Examples representative of every general approach to 1,3-dienes and to dienophilic functional group combinations have been included. There are two questions one might ask in considering the prospective cyclization of a given triene: what are the factors that govern the rate of cyclization? and, for cyclizations that lead to the creation of one or more new chiral centers, what are the factors that govern diastereoselectivity?
These questions are addressed in Chapter Two. The third chapter is devoted to the all-carbon intramolecular Alder ene reaction. The tables in that chapter summarize all examples that could be found in the literature through 1981, with several additional examples from 1982. Leading references to heterocyclic ene reactions are also included in this chapter.
1. The Intramolecular Diels-Alder Reaction: Variations and Scope.- I. Introduction.- II. Range and Preparation of Dienes.- III. Range and Preparation of Dienophiles.- IV. Heterodienes and Dienophiles.- V. Catalysis of the Reaction.- VI. Conclusion.- VII. References.- 2. The Intramolecular Diels-Alder Reaction: Reactivity and Stereocontrol.- I. Introduction.- II. Factors Influencing the Rate of Cyclization.- 1. Influence of Dienophile Substitution on the Rate of Cyclization.- 2. Influence of Diene Substitution on the Rate of Cyclization.- 3. Influence of the Elements Bridging the Diene and Dienophile on the Rate of Cyclization.- a) Effect of Ring Size.- b) Effect of Buttressing.- c) Effect of Heteroatoms in the Bridge on the Rate of Cyclization.- III. Factors Influencing the Stereochemical Outcome of the Cyclization.- 1. Triene Geometry.- 2. Cis vs. Trans Ring Fusion.- a) Preference for an Endo Transition State.- b) Influence of Diene Substitution on the Geometry of Ring Fusion.- c) Influence of the Bridge Between the Diene and the Dienophile on the Geometry of Ring Fusion.- 3. Diastereomeric Control by Remote Chiral Centers.- a) Diastereomeric Control by a Rigid Skew in the Bridge.- b) Diastereomeric Control by a Substituent on the Bridge.- c) Diastereomeric Control by an Alkoxy Substituent on the Bridge.- d) Diastereomeric Control by Chiral Centers not Included in the Bridge.- IV. Summary.- V. References.- 3. The Intramolecular Alder Ene Reaction.- I. Introduction.- II. Reactivity of Ene Acceptors.- 1. Unactivated Olefins.- 2. Activated Olefins.- 3. Acetylenes.- III. Reactivity of Ene Donors.- 1. Unactivated Donors.- 2. Speculations on Activated Donors.- IV. Steric and Stereoelectronic Control Elements in the Intramolecular Ene Reaction.- 1. Cis vs. Trans Relationship of the Two Interacting Side Chains.- 2. Diastereometric Control by Substituents on the Bridge Between the Ene Donor and the Ene Acceptor.- 3. Diastereomeric Control of Carbon-Carbon Bond Formation by Other Remote Substituents.- V. Directions for the Future.- VI. Tables.- 1. Carbocyclic, Type I, Unactivated Olefin Acceptor.- 2. Carbocyclic, Type I, Activated Olefm Acceptor.- 3. Carbocyclic, Type I, Acetylene Acceptor.- 4. Heterocyclic, Type I, Unactivated Olefin Acceptor.- 5. Heterocyclic, Type I, Activated Olefin Acceptor.- 6. Heterocyclic, Type I, Acetylene Acceptor.- 7. Type II.- 8. Type III.- 9. Organometallic.- VII. References.
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