96746-56-4Relevant articles and documents
Kinetics of the reactions of β-methoxy-α-nitrostilbene with methoxyamine and N-methylmethoxyamine. Direct observation of the intermediate in nucleophilic vinylic substitution
Bernasconi, Claude F.,Leyes, Aquiles E.,Eventova, Irina,Rappoport, Zvi
, p. 1703 - 1711 (2007/10/02)
A kinetic and spectroscopic study of the reactions of MeONH2 and MeONHMe with β-methoxy-α-nitrostilbene (1-OMe) in 50% Me2SO-50% water is reported. With MeONHMe, the reaction leads to the expected enamine substitution product, Ph(MeONMe)C=C(Ph)NO2 (1-MMA); with MeONH2 the product at high pH is the anion, MeON=C(Ph)C(Ph)=NO2-, while at low pH it is the imine form MeON=C(Ph)CH(Ph)NO2 rather than the enamine. At high pH and high amine concentrations, the SNV intermediates, Ph(OMe)(MeONR)CC(Ph)=NO2-, with R = H or Me, rise to detectable levels which allows their spectroscopic and kinetic characterizations. These reactions represent the first examples of a nucleophilic vinylic substitution by amine nucleophiles in which the intermediate is directly observable. Structure-reactivity comparisons between the MeONHMe reaction and the reaction of 1-OMe with piperidine and morpholine reported previously are consistent with a relatively weak dependence of the nucleophilic addition step (k1) on amine basicity (βnuc = 0.25) but a strong dependence of the leaving group expulsion step (k2) on amine pKa (βpush = 0.71); this explains why the intermediate is observable in the reaction with the relatively weakly basic MeONH2 and MeONHMe but not with more strongly basic amines. MeONH2 and MeONHMe show the enhanced reactivity expected for α-effect nucleophiles, but it is mainly reflected in an enhanced equilibrium constant for nucleophilic addition while the effect on k1 is relatively small. Steric effects are shown to play a major role in the MeONHMe reaction. One type of steric effect is caused by crowding in the intermediate which reduces the rate and equilibrium constant for intermediate formation and enhances leaving group departure. The other is steric hindrance to π-overlap in the product and the transition state leading to it which reduces the push by the nitrogen lone pair of the intermediate and hence decreases k2 for leaving group expulsion; this latter effect is stronger than the effect of crowding in the intermediate.
Kinetic analysis of elementary steps in nucleophilic vinylic substitution reactions of α-nitro-β-X-stilbenes (X = OCH2CF3, OCH3, NO2) with various nucleophiles.
Bernasconi, Claude F.,Schuck, David F.,Ketner, Rodney J.,Weiss, Minda,Rappoport, Zvi
, p. 11764 - 11774 (2007/10/02)
Rate constants of elementary steps in the addition-elimination mechanism of nucleophilic vinylic substitutions (SNV) were determined by studying the following reactions in 50% Me2SO-50% water at 20 °C: (1) α-nitro-β-(2,2,2-trifluoroethoxy)stilb
Kinetics of reactions of hydroxide ion and water with β-X-substituted α-nitrostilbenes (X = Cl, I, SEt, OMe, SCH2CH2OH) in 50% Me2SO-50% water. Search for the intermediate in nucleophilic vinylic substitution
Bernasconi, Claude F.,Fassberg, Julianne,Killion Jr., Robert B.,Schuck, David F.,Rappoport, Zvi
, p. 4937 - 4946 (2007/10/02)
The hydrolysis of Ph(LG)C=Cph(NO2) (4-LG, Lg = Cl, I, Set, Ome) in basic solution yields the anion of 1,2-diphenyl-2-nitroethanone, PhC(=O)C(=NO2-)Ph (8-), by the addition-elimanation mechanism of nucleophilic v
