Basicity organolithium compounds

Halogen-lithium exchange is an equilibrium process favoring formation of fhe more stable, less basic, organolithium compounds. As shown in Tab. 1.5, fhe equilibrium constants for iodine-lithium exchange of Phi wifh different organolithium compounds (RLi) [40] can be correlated wifh fhe pK of RH. 

A more promising procedure for the formation of alkenes from tosylhydrazones is represented by the Shapiro reaction It differs from the Bamford-Stevens reaction by the use of an organolithium compound (e.g. methyl lithium) as a strongly basic reagent ... 

Organomagnesium and organolithium compounds are strongly basic and nucleophilic. Despite their potential to react as nucleophiles in SN2 substitution reactions, this reaction is of limited utility in synthesis. One limitation on alkylation reactions is competition from electron transfer processes, which can lead to radical reactions. Methyl and other primary iodides usually give the best results in alkylation reactions. 

Since Lewis base additives and basic solvents such as tetrahydrofuran are known to deaggregate polymeric organolithium compounds, (21,23,26) it was postulated that ketone formation would be minimized in the presence of sufficient tetrahydrofuran to effect dissociation of the aggregates. In complete accord with these predictions, it was found that the carbonation of poly(styryl)lithium (eq. 9), poly(isoprenyl)-lithium, and poly(styrene-b-isoprenyl)lithium in a 75/25 mixture (by volume) of benzene and tetrahydrofuran occurs quantitatively to produce the carboxylic acid chain ends (8 ). 

The relative basicity of eighteen organolithium compounds was studied by calorimetric measurements of the compounds dissolved in hexane-Et20 (9 1 by volume) interacting with isopropyl alcohol. The order of exothermicity is shown in equation 32 °. ... 

Lewis bases effect dramatic changes in microstructure, initiation rates, propagation rates, and monomer reactivity ratios for alkyllithium—initiated polymerizations of vinyl monomers (1-6). Some insight into the molecular basis for these observations has been provided by a variety of NMR, colligative property, and light-scattering measurements of simple and polymeric organolithium compounds in hydrocarbon and basic solvents... 

In general, simple alkyllithiums exist predominantly as either hexamers (for sterically unhindered RLi) or tetramers (for sterically hindered RLi) in hydrocarbon solvents and as tetramers in basic solvents (9-12). Polymeric organolithium compounds such as poly(styryl)lithium exist as dimers in hydrocarbon solution and are unassociated in basic solvents such as tetrahydrofuran (13-15). The state of association of poly-(dienyl)lithiums in hydrocarbon solution is a subject of current... 

Lewis bases exert dramatic effects on the rate, stereochemistry, and reaction pathway in organolithium chemistry 4). A partial explanation for these observations can be deduced from the effects of Lewis bases on the degree of association of organolithium compounds as shown in Table 3. In general, the presence of basic molecules tends to decrease the average degree of association of organolithium compounds. Thus, simple alkyllithiums which are hexameric in hydrocarbon solution... 

Pure monomeric forms can be produced if one adds 1-3 equivalents of HMPA (Figure 2.17) to the organolithium compound in diethyl ether or better still in THF solution, since the basic oxygen of this additive is an excellent electron pair donor, as illustrated in Figure 10.3 using the formation of [phenyllithium(HMPA)(THF)2] monomer B as an example. 

The reaction of Grignard reagents and organolithium compounds with aldehydes and ketones is perhaps the most useful method for the preparation of alcohols. The reaction is conducted under basic conditions and proceeds according to the following general mechanism ... 

Reactions involving strongly basic organometallic compounds, e.g. Grignard reagents, organolithiums, and metal hydrides, require the use of carefully dried solvents. Anhydrous solvents (< SOppm of water)... 

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