The reaction ofn-butyllithium with benzoic acid: is nucleophilic addition competitive with deprotonation?
摘要:
An evaluation of a branching vs sequential mechanism for the reaction of benzoic acid with n-butyllithium favors the latter. (C) 1997 by John Whey & Sons, Ltd.
Selectivities in reactions of organolithium reagents with aryl bromides which bear proton-donating groups
摘要:
Studies of substrates which offer an acidic hydrogen and an aryl bromide for reaction with an organolithium reagent have been carried out with a series of benzene bromo amides and bromo anilides as well as selected benzene bromo carboxylic acids, bromoanilines, and bromobenzylamines. A representative example is the reaction of N-ethyl-N-deutero-o-bromobenzamide (6-d) with 1-lithio-3-phenylpropane to give N-ethyl-o-deuterobenzamide (46%, 94%-d) (7-d), N-ethyl-o-bromobenzamide (6)(49%), 3-deutero-1-phenylpropane(51%, 92%-d), and 1-bromo-3-phenylpropane (48%). Product formation in this and related cases is explained by the operation of a two step sequence in which an initial deprotonation is followed by a bromine-lithium exchange which is accelerated with respect to mixing. Such a sequence is consistent with the results of deuterium labeling and with changes in product ratios on different mixing and with differently aggregated organolithium reagents. Support is provided for the operation of two pathways for the expedited bromine-lithium exchange reactions. In one pathway a high local concentration of the organolithium reagent promotes rapid reaction and in the second the exchange reaction occurs within an initially formed complex. The selectivity for removal of a bromine ortho to a lithiated carboxamide is found to be 5-8 with n-butyllithium, and satisfactory synthetic ortho selectivity is obtained for N-ethyl-2,5-dibromobenzamide with phenyllithium.
The reaction of 1-arylpropenyl-lithium (1a–c) with t-alkylbromides proceeds by either a nucleophilic substitution or single electron transfer mechanism, the preferred pathway being a function of electronicsubstituenteffects and the absence or presence of tetramethylethylenediamine or hexamethylphosphoramide.
A Cu-mediated one-pot Michael addition/α-arylation strategy using a diaryliodonium salt: a direct and efficient approach to α-aryl-β-substituted cyclic ketone scaffolds
A direct and efficient construction of [small alpha]-aryl-[small beta]-substituted cyclicketone scaffolds has been achieved using Cu-mediated one-pot Michael addition/[small alpha]-arylation strategy. The reaction features easily available materials, broad substrate scope, moderate to...
Dihydropyridines in Organometallic Synthesis. Formation of Pyridine and Dihydropyridine-Stabilized Alkylidene Complexes of Tungsten(0) and Chromium(0) from Fischer Carbene Complexes: Structure and Reactivity
1,2- and 1,4-dihydropyridines react with alkoxycarbene complexes of chromium and tungsten to give, upon an unprecedented hydride transfer, alcohol elimination, and pyridine fixation on the carbene carbon, a new class of air-stable pyridinium ylide complexes. These pyridine-protected alkylidene complexes of chromium(0) and tungsten(0) were fully characterized by X-ray crystallography. In the case of
Enantioselective Inverse Electron Demand (3 + 2) Cycloaddition of Palladium-Oxyallyl Enabled by a Hydrogen-Bond-Donating Ligand
作者:Yin Zheng、Tianzhu Qin、Weiwei Zi
DOI:10.1021/jacs.0c11504
日期:2021.1.20
Cycloaddition reactions between oxyallylcations and alkenes are important transformations for the construction of ring systems. Although (4 + 3) cycloaddition reactions of oxyallylcations are well-developed, (3 + 2) cycloadditions remain rare, and an asymmetric version has not yet been developed. Moreover, because oxyallylcations are highly electrophilic, only electron-rich olefins can be used as