Photochemical Approach to the Cyclohepta[b]indole Scaffold by Annulative Two-Carbon Ring-Expansion

Area of Science:

• Organic Chemistry
• Photochemistry
• Synthetic Methodology

Background:

• π-donor-π-acceptor chromophores are crucial in various chemical applications.
• Developing efficient methods for molecular expansion and functionalization is essential in organic synthesis.

Purpose of the Study:

• To report the implementation of a photochemical two-carbon homologation strategy.
• To synthesize novel cylohepta[b]indole and indolo[2,3-d]tropone derivatives.
• To elucidate the mechanism of the observed multibond reorganization.

Main Methods:

• Photochemical reaction of a π-donor-π-acceptor chromophore with a phenyl connector.
• Metal-free, one-pot, two-carbon ring expansion.
• Post-irradiation structural elaboration.
• Mechanistic studies using control experiments and computational chemistry.

Main Results:

• Successful synthesis of cylohepta[b]indole building blocks via a two-carbon ring expansion.
• Formation of novel indolo[2,3-d]tropone compounds through post-irradiation modification.
• Establishment of a mechanistic hypothesis for the multibond reorganization process.

Conclusions:

• The developed photochemical method enables efficient two-carbon homologation and ring expansion of chromophores.
• This strategy provides access to valuable indolo[2,3-d]tropone scaffolds.
• The mechanistic insights contribute to the understanding of photochemical multibond reorganization reactions.