Absolute Configuration by X-ray and Circular Dichroism Methods of Calycanthine

Abstract

THE absolute configurations of both (+)-2,5-dimethoxy-7-dimethylaminotriptycene^1,2 and (−)-1,5-diamino-9,10-dihydro-9,10-ethenoanthracene³, as determined by the X-ray technique of Bijvoet^4,5, are antipodal to the absolute configurations obtained from the circular dichroism (CD) spectra by application of molecular exciton theory, as developed by Mason⁶. From the similar CD spectra of related (+)-2,7-disubstituted triptycenes⁷ and (−)-1,5-disubstituted 9,10-dihydro-9,10-etheno- or -ethano-anthracenes³, Tanaka and colleagues have concluded that the contradiction is general. If that is the case and the two techniques have been correctly applied, then the theoretical basis of one or the other is unsound. Tanaka et al.⁷ accept the molecular exciton theory considerations and conclude that “the present method of determining the absolute configuration by the X-ray analysis should be changed so as to give the antipodal configuration”. This is an assertion that all absolute configurations determined by the Bijvoet technique are, and will be, wrong.