Absolute conformation and chiroptical properties. VII. 9(1 ')-msc and Psc forms of 9-(2-fluoro-1,1-dimethylethyl)- and 9-(1,1-dimethylpropyl)-11,12-bis(methoxycarbonyl)-9,10-dihydro-9,10-ethenoanthracenes

The racemic forms of sc-9-(2-fluoro-1,1-dimethylethyl)- and 9-(3-iodo-1,1-d imethylpropyl)-11,12-bis(methoxycarbonyl)-9,10- dihydro-9,10-ethenoanthrace ne were prepared by treatment of the corresponding carboxylic acid with xen on difluoride and by reduction of 9-(1,1-dimethyl-3-oxopropyl) compound fol lowed by a reaction with iodine in the presence of imidazole, respectively. The fluoro and the iodo compounds were resolved on a chiral column. The ab solute conformations of these compounds were determined by deriving them by the same methods from the carboxylic acid and the aldehyde of known absolu te conformations. Reduction of the iodo compound with Raney nickel in 1-pro panol afforded optically active sc-9-(1,1-dimethylpropyl) compound. In the CD spectrum, the Psc-(-) fluoro compound showed a broad and large trough at ca. 240 nm, similarly with the other halogen compounds, and a stronger Cot ton effect at ca. 220 nm than the other halogen compounds. The Psc-(+)-9-(1 ,1-dimethylpropyl) compound showed a quite different CD spectrum from those of other halogen compounds. Thus the importance of the halogen, though rem ote from any chromophore, in determining the CD spectra of the title compou nds and analogous ones was confirmed.