Autoassembling of the cage structures - 11. Absolute configuration and chiroptical properties of 1,4-di-tert-butyl-2,5-dioxabicyclo[2.2.1]heptane-3,6-dione enantiomers

Enantiomeric dilactones ((1R,4R)-(+)-1 and (1S,4S)-(-)-1) of alpha,alpha'-dihydroxy-alpha,alpha'-di-tert-butylglutaric acid have been prepared. The Cotton effect sign of the n-->pi*-transition of the lactone chromophore in enantiomers I is determined by the contribution of the uncompensated bonds of the delta-dilactone ring, but not by that of the gamma-monolactone ring of 1. The correlation of the Cotton effect sign of the n-->pi*-transition with the chirality of the cage structure and the absolute configuration for the series of 1,4-dialkyldilactones of type 1 has been suggested. The contribution of the pseudo-a-oriented amide group to the Cotton effect sign of the lactone n-->pi*-transition (the effect of the third chiral sphere) in diastereomeric lactonamides 2a,b predominates over that of the nonplanar bonds of the heterocycle (over the effect of the second chiral sphere).