Organolithium reagents kinetics

Functionalized organolithium reagents can be prepared and alkylated. The configuration of the dioxanyl reagent 2 proved to be subject to control.85 The kinetically favored trans lithio derivative is converted to the more stable cis isomer at 20° C. Both isomers were methylated with retention of configuration at saturated carbon. 

Reactivity of oxiranes with organolithium reagents TABLE 9. Kinetic resolution of racemic oxiranes using HCLA 53... 

Dimethylpyrimido[4,5-f]pyridazine-5,7-dione 23 and its derivatives undergo attack at both C-3 and C-4. Under conditions of kinetic control, addition occurs preferentially at the more electron-deficient C, whereas thermodynamic control conditions, or the use of bulkier nucleophiles, favor addition at the less hindered position 3. This duality is illustrated by the addition of Grignard and organolithium reagents to C of 3-chloro analogue 24 (Equation 9), whereas stabilized nucleophiles such as the anion of nitromethane add at C-3 (Scheme 10) <2000CHE975>. Displacement of the 3-chloride occurs also upon treatment of 24 with amines (Equation 10) <2000CHE1213>. 

Generation of Enantioenriched, Configurationally Stable Organolithium Reagents. (1 S,2E)-1 -(N.Af-Diisopropyl-carbamoyloxy)-l-methyl-2-butenyllithium-(—)-sparteine is configurationally stable in solution and is obtained by kinetic resolution of the racemic 2-alkenyl carbamate by n-butyllithium-(—)-sparteine with >80% de (eq 4). The enantioenriched allylstan-nane, obtained on y-stannylation, was used as chiral homoenolate reagent. The methoxycarbonylation (a, inversion) yields enantioenriched 3-alkenoates. ... 

Organolithium reagents generally add in 1,2-fashion to a)S-unsaturated carbonyl compounds. This addition takes place rapidly at low temperatures and is kinetically controlled. 

Coordination of the chromium tricarbonyl group onto an arene enhances the kinetic acidity of the aryl C—bonds. In order to avoid nucleophilic attack of the organolithium reagent onto a CO ligand, the reaction has to be run at low temperature. The reaction is regioselective as ortholithiation is observed with arene substituted by OCH3, F, Cl. 

In early investigations, Cohen established a powerful strategy for the synthesis of organolithium reagents based on the reductive cleavage of C-S bonds (Scheme 13.2) [36]. Thioacetals, such as 18/19, constitute a particularly useful class of precursors. Treatment of a mixture of 18 and 19 with LDMAN (20, lithium l-(dimethylamino)naphthalenide) leads to reductive lithiation, thus affording the carbanions 22 and 24 via the radical intermediate 21. Accompanying mechanistic studies revealed that the kinetically pre-... 

Fractional kinetic orders of homogenous reactions in solution may point to association of a particular reagent. The kinetics of the initiation step of styrene polymerization in the presence of n-BuLi (equation 33) is in accordance with the assumption that this organolithium compound in a nonbonding solvent forms aggregates of six molecules on the average" . 

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