On the Absolute Configuration of (+)-Indane-1-carboxylic Acid

Article abstract of DOI:10.1002/hlca.19820650135

The (R)-configuration, attributed to (+)-indane-carboxylic acid ((+)-1) by Fredga, is unequivocally confirmed (Scheme 1).Configurational doubts, raised by an erroneous ORD. curve of (-)-1-methylindane ((-)-4) published by Brewster and Buta, are unfounded (cf. the following paper of Brewster and the corrections in <4>).This was further verified by preparing deuteriated 1-methylindanes starting with (-)-(R)-3-phenylbutyric acid ((-)-(R)-5) as well as with (+)-(R)-1 or (-)-(S)-1 (Scheme 2).The ORD. curves of the optically active 4 thus obtained were (disregarding deuterium isotope effects) identical or antipodal, respectively (cf.Fig.1,2, and 7a-e).Optically active methyl indane-1-carboxylates ((-)-(R)-14 or (+)-(S)-<1-2H>-14) show a strong solvent dependence of their ORD. and CD. spectra with a sign inversion occuring in going from isooctane to methanol or benzene.The observed changes can be explained by a change in the population of comformations where the ester carbonyl group is eclipsed either with the C(1),C(2)- or C(1),H-bond, with the n,?*-transition having a slightly different energy and the ester group an essentially enantiomeric environment with respect to its orientation relative to the benzene moiety.