TADDOL-TICL2 CATALYZED DIELS-ALDER REACTIONS - UNEXPECTED INFLUENCE OF THE SUBSTITUENTS IN THE 2-POSITION OF THE DIOXOLANE RING ON THE STEREOSELECTIVITY
B. Altava et al., TADDOL-TICL2 CATALYZED DIELS-ALDER REACTIONS - UNEXPECTED INFLUENCE OF THE SUBSTITUENTS IN THE 2-POSITION OF THE DIOXOLANE RING ON THE STEREOSELECTIVITY, Tetrahedron : asymmetry, 8(15), 1997, pp. 2561-2570
Several (3,5-dimethylphenyl)-1,3-dioxolane-4,5-demethanols have been s
ynthesized, and their TiCl2 derivatives used as catalysts in the react
ion of cyclopentadiene with (E)-2-butenoyl-1,3-oxazolidin-2-one. The s
ubstituents in the 2-position of the dioxolane ring exert a decisive i
nfluence on the extent and direction of the asymmetric induction and,
consequently any possible enantiomer of the cycloadducts can be prefer
entially obtained by changing these substituents. Molecular mechanics
calculations of the structures and relative energies of the possible d
ienophile-catalyst complexes offer a tentative explanation for the res
ults described. (C) 1997 Elsevier Science Ltd.