63361-59-1Relevant articles and documents
Base-Strength Effects in Syn Eliminations from trans-2,3-Dichloro-2,3-dihydrobenzofuran in Dimethyl Sulfoxide
Baciocchi, Enrico,Ruzziconi, Renzo,Sebastiani, Giovanni V.
, p. 827 - 830 (1980)
Syn eliminations from trans-2,3-dichloro-2,3-dihydrobenzofuran (1), to give 3-chlorobenzofuran, promoted by substituted phenoxides (substituents: p-CH3, H, p-Br, p-Cl, m-NO2) and 4-chloro-2-nitroanilide anion have been investigated in 99percent Me2SO.The reaction rate is very sensitive to the base strength, and from the Broenstedt plot a β value of 0.67 can be calculated.Introduction of a chlorine substituent at the 5-position causes a 19-fold rate increase for the reaction with phenoxide ions, and with the same base a kH/kD value (in comparison with the 3-deuterated counterpart of 1) of 2.4 is observed.These values clearly suggest that the reaction of 1 occurs by a highly carbanionic transition state.The substituent effect and kH/kD value remain, however, substantially unchanged when the base strength is changed, thus indicating that the transition-state structure of the eliminations from 1 is not significantly influenced by the strength of the attacking base.These results are discussed in the light of the current theories concerning the effects of structural changes on the E2 transition state.
Anti and Syn Eliminations from 2,3-Dihalo-2,3-dihydrobenzofurans. The Role of the Substrate Structure and the Base-Solvent System on the Reaction Mechanism
Baciocchi, Enrico,Ruzziconi, Renzo,Sebastiani, Giovanni V.
, p. 6114 - 6120 (2007/10/02)
The anti and syn β-eliminations from a series of 31 2,3-dihalo-2,3-dihydrobenzofurans (to give 3-halobenzofuran) have been kinetically investigated in t-BuOK-t-BuOH, in the presence and in the absence of 18-crown-6 ether (18C6), and in EtOK-EtOH.Reaction mechanisms have been assigned on the basis of leaving group, kinetic deuterium isotope, ring substituent (5-chlorine), and β-halogen effects.These data have provided information concerning structure and solvent effect on the mechanism of β-elimination reactions that lead to the following conclusions: (a) an E1cBI mechanism is likely to be operating, regardless of stereochemistry, with chlorine as β-activating atom and fluorine as the leaving group and (b) an E2 reaction is likely to be operating for the opposite structural situation, i. e., with β-fluorine activation and chlorine as the leaving group.The mechanism is likely to change from E2 to E1cBI as the reaction stereochemistry changes from anti to syn and as we move from EtOK-EtOH to t-BuOK-t-BuOH and from here to t-BuOK-t-BuOH-18C6.
