부산대학교 도서관

The diastereoselective and enantioselective intramolecular Diels-Alder reactions of 1,7,9-decatrien-3-ones to cisor trans-octalin derivatives were systematically investigated in the presence of different Lewis acids and chiral ligands. The best cis-selective promoter, consisting of diethylaluminum chloride and (R)-1,1'-bi-2-naphthol (BINOL), provided an enantiomeric excess (ee) of only 33%. For the trans-selective reactions, dichlorotitanium diisopropoxide was the best Lewis acid, and a 2-naphthyl-substituted (R,R)-α,α,α',α'-tetraaryl-1,3-dioxolane-4,5-dimethanol ligand (TADDOL) furnished excellent diastereoselectivities and enantioselectivities in the range of 50-68%. Subsequent reactions of a typical trans-octalin derivative led to compounds, which enabled the determination of the absolute configuration of the favored enantiomer and a deduction of the involved reaction mechanism. Interpretation of the NMR shifts of the enantio-enriched Mosher esters and an X-ray structure analysis were the keys for this structural assignment. We could demonstrate that Mosher analyses do not necessarily rely on enantiopure samples. [ABSTRACT FROM AUTHOR]