Preparation of Substituted Dihydrofluorenones by Photoisomerization of Benzotropolone Derivatives

Abstract

The photoisomerization of the Diels–Alder adduct formed between tetramethylpurpurogallin and maleic anhydride is described. The process is highly stereoselective, involves the β,γ-unsaturated ketone chromophore present in the adduct, proceeds through the formation of allyl and aroyl radical intermediates, and leads to a novel substituted dihydrofluorenone in good yields.

Keywords:

• Benzotropolones
• Diels–Alder reaction
• photoisomerization
• substituted dihydrofluorenones
• β,γ-unsaturated ketone chromophores

ACKNOWLEDGMENTS

Financial support from the Agencia Nacional de Investigación e Innovación, the Comision Sectorial de Investigación Científica, the National Science Foundation, and the Royal Society of Chemistry is acknowledged. We also thank Alexander Khrizman for technical support.