173778-56-8Relevant articles and documents
Control of Diastereo- and Enantioselectivity in Metal-Catalyzed 1,3-Dipolar Reactions of Nitrones with Alkenes. Experimental and Theoretical Investigations
Gothelf, Kurt V.,Hazell, Rita G.,Jorgensen, Karl Anker
, p. 346 - 355 (1996)
The scopes and limitations of the catalytic effects of achiral and chiral Mg(II) and Cu(I) complexes on the stereochemistry of the 1,3-dipolar cycloaddition reaction of nitrones with alkenes have been investigated.A remarkable high degree of endo-selectivity (endo/exo > 20) is induced in the 1,3-dipolar cycloaddition reaction by the presence of a catalytic amount of, especially, a Mg(II)-phenanthroline complex.The diastereochemical assignement of the product is confirmed by an X-ray crystalographic determination of the exo-isoxazoline.By the reaction of an alkene bearing a chiral auxiliary, with different nitrones and a catalytic amount of the Mg(II)-phenanthroline complex, one of four possible diastereomers of the isoxazolines is exclusively formed.The absolute stereochemistry of this product is also assigned by an X-ray crystallographic investigation.The presence of a catalytic amount of a chiral Mg(II)-bisoxazoline complex in the 1,3-dipolar cycloaddition reaction leads to high endo-selectivity and occasionally with an ee > 80percent.The reaction mechanism of the Mg(II)-catalyzed reaction is discussed on the basis of the experimental results and semiempirical chemical calculations.The calculations are used to account for the catalytic effect of the Mg(II)-ligand complexes and to determine transition state energies for both the uncatalyzed and Mg(II)-ligand-catalyzed reactions.
