Mechanism of the Deprotonation Reaction of Alkyl Benzyl Ethers with n‐Butyllithium

Abstract

Kinetic study of the α-lithiation of benzyl methyl ether (BME) by nBuLi has revealed that increasing the concentration of the organolithium compound does not necessarily increase the reactivity, and this is a consequence of the reactivities of the different nBuLi aggregates present in solution. We propose a dimer-based mechanism, in which a pre-complexation step is a key process for substrates bearing a donor oxygen atom that can interact with the lithium cation to form mixed dimers. For these studies, we have developed a system based on UV/Vis spectroscopy that allows kinetic measurements to be conducted at -80 °C under argon.

Reversible Lithium Storage at Highly Populated Vacant Sites in an Amorphous Vanadium Pentoxide Electrode

“…To reduce the irreversible reaction, a -V 2 O 5 was treated with n -BuLi, which is a strong base that reacts with acidic surface hydroxyl groups. , An expectation here is the decrease of H 2 evolution due to the removal of surface hydroxyl groups. Figure a shows the FT-IR spectra for two a -V 2 O 5 samples.…”

The Two Alternative Rate-Determining Steps in Benzylic Lithiation Reactions of Esters and Carbamates

“…Because reactivity is strongly dependent on n- BuLi aggregation, the lithiation of benzyl ether 1 follows a pathway in which n -BuLi tetramer–dimer deaggregation occurs in a fast equilibrium step, followed by dimer complexation to the oxygen atom of the ether, and a subsequent proton transfer as the rate-determining step . When the same mechanistic scheme is applied to the lithiation of ester 2 , a rate equation is obtained, k obs = K 1 k 2 [dimer] ( K 1 and k 2 being the precomplexation equilibrium and proton transfer rate constants respectively), which predicts a linear dependence between the observed rate constant and [dimer] (see Figure , right).…”

“…Our studies on the lithiation of benzyl methyl ether ( 1 ) (Figure ) with n -BuLi in THF/hexane at −80 °C showed that a precoordination step between base and acid occurs prior to the rate-determining proton transfer reaction. We now describe the results of a study on the lithiation of benzyl ester 2 and carbamate 3 , substrates analogous to ether 1 in which the O -substituents show enhanced donor ability.…”

“…Because reactivity is strongly dependent on n-BuLi aggregation, 10 the lithiation of benzyl ether 1 follows a pathway in which n-BuLi tetramer−dimer deaggregation occurs in a fast equilibrium step, followed by dimer complexation to the oxygen atom of the ether, and a subsequent proton transfer as the rate-determining step. 9 When the same mechanistic scheme is applied to the lithiation of ester 2, a rate equation is obtained,…”

Base or nucleophile? DFT finally elucidates the origin of the selectivity between the competitive reactions triggered by MeLi or LDA on propanal

“…13 Similarly, Garcia-Rio et al have identified, by kinetics and NMR measurements, a dimer of n-BuLi solvated by 3 THF and on which the substrate of a deprotonation docks before the reaction starts. 14 The situation is also very clear for LDA, the disolvated dimer (LDA) 2 -2THF of which has been depicted in solution. 15 The electrophile we have retained is propanal, viz.…”