[10]annulene: Electrocyclization mechanisms

Area of Science:

• Organic Chemistry
• Computational Chemistry

Background:

• [10]annulene isomers undergo 6-π electrocyclization to form 4a,8a-dihydronaphthalene.
• Understanding the reaction mechanism and stereochemical outcomes is crucial for synthetic chemistry.

Purpose of the Study:

• To elucidate the detailed quantum-chemical mechanism of 6-π electrocyclization for all-cis, mono-trans, and double-trans [10]annulene isomers.
• To compare computational predictions with experimental findings for these cyclization reactions.

Main Methods:

• Utilized various quantum-chemical methods to explore reaction pathways.
• Analyzed transition states and energy profiles for different [10]annulene configurations.

Main Results:

• Mono-trans [10]annulene preferentially cyclizes to trans-4a,8a-dihydronaphthalene, aligning with experimental data.
• All-cis [10]annulene requires a rate-limiting bond shift to a double-trans naphthalene-like conformation before electrocyclization to cis-4a,8a-dihydronaphthalene.
• Computed rate coefficients for all-cis cyclization match experimental values, supporting the proposed mechanism.

Conclusions:

• The study confirms the distinct cyclization pathways for different [10]annulene isomers.
• Computational results validate the stereochemical assignments of isolated isomers by Masamune et al.