Preparation of substituted dihydrofluorenones by photoisomerization of benzotropolone derivatives

摘要

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.