1,3-HYDRON TRANSFER IN SOME 5- AND 7-SUBSTITUTED 1-METHYLINDENES. ENANTIOSELECTIVITIES AND ENANTIOMER-DEPENDENT KINETIC ISOTOPE EFFECTS

Article abstract of DOI:10.1002/poc.610080604

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 <(k_H/k_D)⁺ and (k_H/k_D)^-> were determined at 20 deg C using (+)-(8R,9S)-dihydroquinidine as chiral catalyst in the solvent o-dichlorobenzene.The rate constants vary according to the electronic effects of the substituents.The primary deuterium KIE, ranging from 4.73 to 11.3 , 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^- > 1; all substrates used are (+)-(S)/(-)-(R)>.The enantiomer dependence of the KIE is most pronounced for 1 <(k_H/k_D)⁺ = 5.71 and (k_H/k_D)^- = 6.46> and vanishes for the most acidic substrates (4 and 5).