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.
Room-temperature Suzuki-Miyaura coupling of heteroaryl chlorides and tosylates
Yang, Junfeng,Liu, Sijia,Zheng, Jian-Feng,Zhou, Jianrong
supporting information, p. 6248 - 6259,12 (2020/09/16)
Suzuki-Miyaura coupling of heteroaryls is an important method for the preparation of compound libraries for medicinal chemistry and materials research. Although many catalysts have been developed, none of them have been generally applicable to the coupling reactions of heteroaryl chlorides and tosylates at room temperature. We discovered that a catalyst combination of Pd(OAc)2 and XPhos (2-dicyclohexylphosphanyl-2',4',6'- triisopropylbiphenyl) could efficiently catalyze these couplings. Besides the choice of catalyst, the use of hydroxide bases in an aqueous alcoholic solvent was essential for fast couplings. These conditions promoted fast release of active catalyst (XPhos)Pd0, and accelerated the transmetalation in the catalytic cycle. Most of the major families of heteroaryl chlorides (31 examples) and tosylates (17 examples) reached full conversion within minutes to hours at room temperature. The method could be easily scaled up for gram-scale synthesis. Furthermore, we examined the relative reactivity of coupling partners in whole reactions. Electron-rich heteroaryl chlorides and tosylates reacted more slowly than electron-deficient ones, in the order of indole, pyrrole furan, thiophene > pyridine. Similarly, electron-deficient arylboronic acids were less reactive than electron-neutral and electron-rich ones. The reactivity trends from this study can help to choose appropriate coupling partners for Suzuki reactions.
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.
