The products derived from the acid-catalyzed dehydration of 4-hydroxy-2,3,4-triphenyl-2-cyclopentenone

Protonation of Tetraphenyl‐ and 2,3,4‐Triphenylcyclopentadienone – An NMR and X‐ray Crystallographic Study

“…Many of the reported products were characterized from their 1 H NMR, UV and mass spectra. On the basis of its spectra and its Diels–Alder reaction with DMAD to form 31 , dimer 30 was suggested to be a crucial intermediate . We now report the isolation and X‐ray crystal structure of 30 that not only confirms its identity, but also provides a rationale for its conversion to the tetracyclic system 32 (Scheme ).…”

“…The acid‐catalyzed dehydration of 4‐hydroxy‐2,3,4‐triphenylcyclopent‐2‐en‐1‐one ( 28 ), which leads to the short‐lived species 2,3,4‐triphenylcyclopentadienone ( 29 ), has been extensively studied . Many of the reported products were characterized from their 1 H NMR, UV and mass spectra.…”

“…In the original report of the isolation of the dienone 30 , identification was based mainly on its IR and UV spectra as well as 1 H NMR spectroscopic data acquired at 60 MHz . Fortunately, due to the availability of a 600 MHz spectrometer, a more complete analysis is now achievable (for 1 H, 13 C, HSQC, HMBC and TOCSY spectra, see the Supporting Information).…”

“…Protonation of 2,3,4‐triphenylcyclopentadienone: 4‐Hydroxy‐2,3,4‐triphenylcyclopenten‐1‐one (653 mg. 2.00 mmol) dissolved in dry dichloromethane (10 mL) under nitrogen was treated with HCl (7.50 mL of a 4 m solution in dry dioxane, 30 mL) and heated at reflux for 20 h. The red solution was cooled to room temperature and the solvent removed under vacuum. Chromatography on silica using dichloromethane/pentane (1:4) as eluent gave an intensely coloured blue solid (4 mg), now known to be 33 ,, and 2‐(2′‐oxo‐3′,4′,5′‐triphenylcyclopent‐3′‐enyl)‐3,4,5‐triphenylcyclopenta‐2,4‐dienone ( 30 ) (100 mg, 0.162 mmol; 16 %), m.p. 208–209 °C (lit.…”