16.13 : Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Conjugated systems with an odd number of π-electron pairs undergo a disrotatory ring closure. For example, (2E,4Z,6E)-2,4,6-octatriene, a conjugated diene containing three π-electron pairs, yields cis-5,6-dimethyl-1,3-cyclohexadiene.
From Chapter 16:
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16.13 : Thermal Electrocyclic Reactions: Stereochemistry
Dienes, Conjugated Pi Systems, and Pericyclic Reactions
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16.1 : Structure of Conjugated Dienes
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16.2 : Stability of Conjugated Dienes
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16.3 : π Molecular Orbitals of 1,3-Butadiene
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16.4 : π Molecular Orbitals of the Allyl Cation and Anion
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16.5 : π Molecular Orbitals of the Allyl Radical
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16.6 : Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene
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16.7 : Electrophilic 1,2- and 1,4-Addition of X<sub>2</sub> to 1,3-Butadiene
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16.8 : Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control
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16.9 : UV–Vis Spectroscopy of Conjugated Systems
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16.10 : UV–Vis Spectroscopy: Woodward–Fieser Rules
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16.11 : Pericyclic Reactions: Introduction
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16.12 : Thermal and Photochemical Electrocyclic Reactions: Overview
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16.14 : Photochemical Electrocyclic Reactions: Stereochemistry
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16.15 : Cycloaddition Reactions: Overview
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