STEREOCHEMICAL STUDIES OF BICYCLO[5.3.1]UNDECANE-8,11-DIONE - CONFORMATIONAL-ANALYSIS, ENANTIOMER SEPARATION, CD-SPECTROSCOPY AND ENOLIZATION

The stereochemical properties of the title compound have been examined by various methods. Dynamic NMR spectroscopy shows the existance of t wo conformers or sets of conformational families separated by a barrie r of 8.2+/-0.4 kcal/mol. At low temperatures only one conformer was ap preciably populated. Chromatographic enantiomer enrichment was perform ed on a microcrystalline triacetylcellulose column and the circular di chroism (CD) spectrum was recorded. The conformational space was explo red by MM3 calculations giving six conformers within 2 kcal/mol. The h igh energy barrier observed by DNMR was assigned a chair-boat inversio n of the eight-membered ring. The CD spectrum of the conformational mi xture given by the MM-computations was calculated by the method develo ped by Schellman, giving information about the absolute configuration of the first eluted enantiomer, and about the conformational mixture i n solution. Formation of enol esters under equilibrium conditions gave 83% of the bridgehead enol ester. (C) 1997 Elsevier Science Ltd.