Control of Diastereo- and Enantioselectivity in Metal-Catalyzed
1,3-Dipolar Cycloaddition Reactions of Nitrones with Alkenes.
Experimental and Theoretical Investigations
Kurt V. Gothelf
Rita G. Hazell
Karl Anker Jørgensen
10.1021/jo951204e.s001
https://acs.figshare.com/articles/journal_contribution/Control_of_Diastereo-_and_Enantioselectivity_in_Metal-Catalyzed_1_3-Dipolar_Cycloaddition_Reactions_of_Nitrones_with_Alkenes_Experimental_and_Theoretical_Investigations/3700827
The scopes and limitations of the catalytic effects of
achiral and chiral Mg(II) and Cu(II) complexes
on the stereochemistry of the 1,3-dipolar cycloaddition reaction of
nitrones with alkenes have been
investigated. A remarkably high degree of
<i>endo-</i>selectivity (<i>endo</i>/<i>exo</i> > 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 assignment of the
product is confirmed by an X-ray
crystallographic determination of the structure of the
<i>exo</i>-isoxazolidine. 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
isoxazolidines 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
<i>endo-</i>selectivity and occasionally with an ee >
80%.
The reaction mechanism of the Mg(II)-catalyzed reaction is
discussed on the basis of the
experimental results and semiempirical quantum 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.
1996-01-12 00:00:00
quantum chemical calculations
reaction mechanism
cycloaddition
endo
Mg
dipolar
transition state energies
chiral
diastereochemical assignment
Theoretical Investigations