Absolute Conformation and Chiroptical Properties. III. Optically Active Methyl sc-3-Methyl-3-(substituted 9-triptycyl)butanoate Rotamers

Abstract

Abstract Enantiomers of the title rotamers were resolved by the diastereomer method with use of optically active camphorsultam. The absolute conformations about the C9–Calkyl single bond were determined by the X-ray analysis of one of the diastereomeric amides. All the samples submitted to the X-ray analysis showed their absolute conformation to be Psc. Specific rotations of the Psc methyl esters of the methyl, methoxy, and chloro compounds at the Na D line were positive, whereas that of the fluoro compound negative. Although the absolute conformation of the methyl compound had been predicted, though not conclusive, to be Msc for the dextrorotatory isomer from calculation, it is proved to be Psc. Optical rotations and CD spectra were measured and these chiroptical properties were compared with each other. The chiral methyl esters showed similar patterns in CD spectra if their absolute conformations are the same, irrespective of the kinds of substituents in the benzene ring. Features of molecular structures of the triptycene compounds are also compared and the effects of substituents on the structural parameters are discussed.