Competitive processes in the hydration of dicarbonyl .eta.5-(cyclopentadienyl) alleneiron cations

cis-1,2-Bis(9-anthryl)ethylene. Prearation and photochemical properties

“…A solution of anthrone (2 g) in acetic acid (10 mL) containing concentrated hydrochloric acid (1.2 mL) and granulated zinc (1.2 g) was refluxed for 2.5 h. After cooling the reaction mixture to room temperature, the crystalline precipitate was removed by filtration, washed successively with acetic acid, dilute hydrochloric acid, and water, and then dried (yield 1.69 g). Column chromatography (SÍO2/CH2CI2) gave 0.60 g of g.O'-bianthryl (33%), and 0.84 g (43%) of anthrapinacolin (5) (aromatic C), 202.5 ppm (CO). The aromatic carbons of the 9,10-dihydroanthracene moiety are pairwise equivalent.…”

“…When the temperature is lowered, the overlapping two-proton absorption first separates into two broad bands which finally give rise to an additional AB spectrum («7 = 14.5 Hz). This finding leaves no doubt that anthrapinacolin actually has the previously rejected dibenzocycloheptadienone structure 5 in which the methylene protons of the seven-membered ring become magnetically nonequivalent as the intramolecular mobility of the ring system decreases. From the observed coalescence temperature of about 5 °C, the free energy of activation for the folding motion of the cycloheptadienone ring was calculated9 to be 13 kcal/mol.…”

“…The existence of two geometrical isomers of dianthrylethylene was first mentioned in a spectroscopic context in 1963 when cis-dianthrylethylene was reported to be formed in the thermal decomposition of 9-anthralazine at 270-290 °C and when its spectral properties were described.6-8 However, we have recently pointed out that (5) Becker, H.-D.; Sandros, K.; Hansen, L. J. Org. Chem.…”