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-dimethylpropyl)-11,12-bis(methoxycarbonyl)-9,10-dihydro-9,10-ethenoanthracene were prepared by treatment of the corresponding carboxylic acid with xenon difluoride and by reduction of 9-(1,1-dimethyl-3-oxopropyl) compound followed by a reaction with iodine in the presence of imidazole, respectively. The fluoro and the iodo compounds were resolved on a chiral column. The absolute conformations of these compounds were determined by deriving them by the same methods from the carboxylic acid and the aldehyde of known absolute conformations. Reduction of the iodo compound with Raney nickel in 1-propanol 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 Cotton 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 remote from any chromophore, in determining the CD spectra of the title compounds and analogous ones was confirmed.