Unequal primary kinetic isotope effects in the base-catalysed H–D exchange of diastereotopic protons

Fraser, Robert R.; Champagne, Philippe

doi:10.1139/v80-012

Cited by 8 publications

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1,3‐Hydron transfer in some 5‐ and 7‐substituted 1‐methylindenes. Enantioselectivities and enantiomer‐dependent kinetic isotope effects

Aune

Bergson

Matsson

1995

J of Physical Organic Chem

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Base‐catalysed substrate‐enantioselective 1,3‐hydron transfer (kinetic resolution) was studied in the indene system. A series of 1‐methylindenes substituted in the aromatic ring [5‐methoxy‐ (2), 5‐fluoro‐ (3), 5‐nitro‐ (4) and 7‐nitro (5)] and 1‐methylindene (1) were employed as substrates. The rate constants, the enantioselectivities and the kinetic isotope effects (KIEs) for the enantioselective reactions [(kH/kD)+ and (kH/kD)−] were determined at 20°C using (+)‐(8R, 9S)‐dihydroquinidine as chiral catalyst in the solvent o‐dichlorobenzene. The rate constants vary according to the elecronic effects of the substituents. The primary deuterium KIE, ranging from 4·73 [for (+)‐(S)‐2] to 11·3 [for (−)‐(R)‐5], is correlated with the rate constants as expected on the basis of the Melander–Westheimer postulate. The introduction of a substituent in the aromatic ring decreases the enantioselectivity. All compounds except 5 show the same sense of the enantioselectivity [k+/k− > 1; all substrates used are (+)‐(S)/(−)‐(R)]. The enantiomer dependence of the KIE is most pronounced for 1 [(kH/kD)+ = 5·71 and (kH/kD)− = 6·46] and vanishes for the most acidic substrates (4 and 5).

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