Sensitivity of circular dichroism of β-diketones to minute changes in the orientation of chromophores

Synthesis and CD spectroscopic study of chiralC2-symmetric (+)-2-oxaadamantane-4,8-dione

The enantiomerically pure (-)-(1R,3S,4S,6R,8R)-4-bromo-3-methoxy-2-oxatricyclo[4.3.1.0(3,8)]decan-10-one 1 was transformed into a chiral C2-symmetric molecule (+)-(1R,3R,5R,7R)-2-oxatricyclo[3.3.1.1(3,7)]decane-4,8-dione (2-oxaadamantane-4,8-dione) 2 by a silver nitrate promoted molecular rearrangement/debromination reaction. The Cotton effect in the circular dichroism spectrum of the C2-symmetric (+)-2-oxaadamantane-4,8-dione was studied to prove the absolute configuration.

Determination of the absolute configuration of bicyclo[3.3.1]nonane-2,7-dione by circular dichroism spectroscopy and chemical correlation

A study of the enantiomers of bicyclo[3.3.1]nonane-2,7-dione, a chiral molecule containing two carbonyl chromophores, was performed. Enantiomers of this structure were obtained by HPLC resolution and the (+)-(1R,5S)-enantiomer by enantiospecific synthesis from(+)-(1S,5S)-bicyclo[3.3.1]nonane-2,6-dione. The title structure is an interesting molecule to demonstrate the validity of the octant rule. The location of the major chair-chair conformer into octants placing each chromophore into the origin of the octants led to the opposite configuration assignments. In order to prove unequivocally absolute configuration, enantiospecific synthesis of the title compound was carried out. The kinetic resolution of racemic bicyclo[3.3.1]nonane-2,6-dione using baker's yeast afforded (+)-(1S,5S)-2,6-dione. Employing a reaction sequence analogous to one developed earlier by us with racemic substrates led to carbonyl group shift giving enantiomerically pure (+)-(1R,5S)-bicyclo[3.3.1]nonane-2,7-dione. The absolute configuration of the investigated compound was established by combined use of the octant rule and chemical correlation.