Rational Design and Reaction Mechanism Study of the Photochemical Rearrangement of Fulvene Derivatives

Area of Science:

• Organic Photochemistry
• Computational Chemistry
• Reaction Mechanism Elucidation

Background:

• Photochemistry offers efficient organic synthesis routes.
• UV light-triggered synthesis of spiro[2,4]heptadiene from fulvenes was recently reported but lacks mechanistic understanding.
• Uncharacterized intermediates hinder the application of this novel photochemical reaction.

Purpose of the Study:

• To elucidate the mechanism of UV light-induced photorearrangement cyclopropanation of fulvenes.
• To design and synthesize novel fulvene derivatives for mechanistic studies.
• To identify critical intermediates and reaction pathways.

Main Methods:

• Theoretical design of fulvene derivatives using second-order n-electron valence state perturbation theory.
• Synthesis of representative fulvene derivatives.
• Time-resolved transient absorption spectroscopy (TA) for intermediate characterization.
• Photoproduct analysis.

Main Results:

• Second-order n-electron valence state perturbation theory proved essential for accurate theoretical characterization.
• Designed fulvenes underwent photorearrangement cyclopropanation.
• Key intermediates in intramolecular hydrogen atom transfer and cyclization were identified via TA spectroscopy.
• Complete reaction pathways were proposed.

Conclusions:

• The detailed mechanism of the fulvene photorearrangement cyclopropanation reaction was revealed.
• The study highlights the importance of selecting appropriate theoretical methods for molecular design and mechanistic studies.
• This work facilitates broader applications of this photochemical synthesis.