Carey

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Pericyclic Reactions
Carey Sundberg Part A Chapter 11 Carey
Sundberg Part B Chapter 6 Fleming, Chapter 4
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Pericyclic Reactions  Introduction/Definitions
A pericyclic reaction is characterized as a
change in bonding relationships that takes place
as a continuous, concerted reorganization of
electrons.
The term "concerted" specifies that there is one
single transition state and therefore no
intermediates are involved in the process. To
maintain continuous electron flow, pericyclic
reactions occur through cyclic transition states.
More precisely The cyclic transition state must
correspond to an arrangement of the participating
orbitals which has to maintain a bonding
interaction between the reaction components
throughout the course of the reaction.
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Major Categories of Pericyclic Reactions
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Major Categories of Pericyclic Reactions
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Major Categories of Pericyclic Reactions
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Analysis of Pericyclic Processes
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Electrocyclic Reactions
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Electrocyclic Ring Closing/Opening
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Electrocyclic Reactions Stereochemical
Considerations
It was noted that butadienes undergo conrotatory
closure under thermal conditions, while
hexatrienes undergo disrotatory closure under
thermal conditions. The microscopic reverse
reactions also occur with the same rotational
sense (i.e. cyclobutenes open in a conrotatory
sense when heated, and cyclohexadienes open in a
disrotatory sense when heated.)
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Molecular Orbitals in Conjugated Systems
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FMO Treatment of Electrocyclic Reactions
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FMO Treatment of Electrocyclic Reactions
Photochemical activation
When light is used to initiate an electrocyclic
rxn, an electron is excited from ?2 to ?3.
Treating ?3 as the HOMO now shows that
disrotatory closure is allowed and conrotatory
closure is forbidden.
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Sigmatropic Rearrangements
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Sigmatropic Rearrangements
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1,2 Sigmatropic Rearrangements
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Sigmatropic Rearrangements
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Sigmatropic Rearrangements
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Sigmatropic Rearrangements
1,3
1,5
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Examples of Sigmatropic Rearrangements/Shifts
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Sigmatropic Rearrangements
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2,3 Sigmatropic Rearrangements
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2,3 Sigmatropic Rearrangements
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Examples of 2,3 Sigmatropic Rearrangements
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Coupled 2,3 Sigmatropic Rearrangement/ Reductive
Cleavage
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2,3 Sigmatropic Rearrangements Transition
State Structures
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2,3 Sigmatropic Rearrangements in Synthesis
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Sigmatropic Rearrangements
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3,3 Sigmatropic Rearrangements
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3,3 Sigmatropic Rearrangements
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3,3 Sigmatropic Rearrangements
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3,3 Sigmatropic Rearrangements
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3,3 Sigmatropic Rearrangements
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3,3 Sigmatropic Rearrangements
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Complex Total Synthesis An Introduction
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Complex Total Synthesis An Introduction
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Complex Total Synthesis An Introduction
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Complex Total Synthesis An Introduction
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Complex Total Synthesis An Introduction
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Complex Total Synthesis An Introduction
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Complex Total Synthesis An Introduction
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The Claisen Rearrangement
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Traditional Claisen Rearrangements
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The Claisen Rearrangement in Cyclic Systems
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Synthesis of Allyl Vinyl Ethers
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Other Claisen Variants
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Other Claisen Variants
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Introduction to Retrosynthesis
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Introduction to Retrosynthesis
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Introduction to Retrosynthesis
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Introduction to Retrosynthesis
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Introduction to Retrosynthesis
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Introduction to Retrosynthesis
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Introduction to Retrosynthesis
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Acyclic Chirality Transfer in the Claisen
Rearrangement
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Acyclic Chirality Transfer in the Claisen
Rearrangement