Organolithium reagents, addition mechanism

Mechanisms for the addition of organolithium reagents have been investigated... 

Mechanisms for the addition of organolithium reagents have been investigated much less.434 Addition of a cryptand that binds Li+ inhibited the normal addition reaction, showing that the lithium is necessary for the reaction to take place.43s... 

The mechanism of 1,2-nucleophilic addition is the same as already described. It is found that Grignard reagents and organolithium reagents will react with a,p-unsaturated aldehydes and ketones in this way and do not attack the p-position ... 

Wittig-type olefinations can also be performed using selenoaldehydes. Phosphorus ylides initially attack the carbon atom of the selenocarbonyl functionality.405 Aromatic selenoketones undergo reductive dimerization with organo-lithium reagents probably via an electron transfer mechanism.406 Also the addition of organolithium reagents takes... 

This reaction follows the general mechanism for nucleophilic addition (Section 20.2A)—that is, nucleophilic attack by a carbanion followed by protonation. Mechanism 20.6 is shown using R"MgX, but the same steps occur with organolithium reagents and acetylide anions. 

With organolithium reagents, stable intermediates are produced by addition to a carboxylic acid. On workup, these intermediates produce ketones. As with Grignard reagents, the reaction of organolithium reagents with esters produces tertiary alcohols because the intermediates decompose to ketones under the reaction conditions. The mechanisms for these processes are illustrated in the examples that follow. 

Evidence for a radical coupling mechanism (as opposed to a carbanionic carbonyl addition mechanism) in the intramolecular Smh-promoted Barbier reactions has come from studies on appropriately functionalized substrates in the 3-keto ester series. It is well known that heterosubstituents are rapidly eliminated when they are adjacent to a carbanionic center. Indeed, treatment of a 3-methoxy organic halide (suitably functionalized for cyclization ) with an organolithium reagent leads only to alkene (equation 48). No cyclized material can be detected. On the other hand, treatment of the same substrate with Sml2 provides cyclized product and a small amount of reduced alcohol, with none of the alkene detected by gas chromatographic analysis (equation 49). ... 

The first prominent catalytic asymmetric Michael-type addition reaction of an organolithium reagent was shown by the reaction of 1-naphthy[lithium with 1-fluoro-2-naphthylaldehyde imine in the presence of 6 to afford the binaphthyls in high ee. Only catalytic amounts of 6 (0.05 mol%) effects the reaction to give 82% ee, in which an enantioselective Michael-type addition-elimination mechanism is operative (Eq. (12.12)) [31],... 

The first prominent catalytic asymmetric addition of an organolithium reagent was realized in the reaction of 1-naphthyllithinmwith l-fluoro-2-naphthy-laldehyde imine in the presence of the chiral diether 1 to afford chiral binaphthyls in over 82% ee (Scheme 2). Merely a catalytic amount of 1 (5 mol %) is required to effect the reaction, in which an enantioselective conjugate addition-elimination mechanism is operative [18]. 

Esters react with two equivalents of an organolithium reagent to yield a tertiary alcohol in which two of the alkyl groups are derived from the organolithium reagent (Following fig.). The mechanism of the reaction is the same as that described in the Grignard reaction, i.e., nucleophilic substitution to a ketone followed by nucleophilic addition. 

Show what products result from the addition of Grignard and organolithium reagents to acid derivatives, and propose mechanisms for these reactions. 

Mechanism 22.14 Addition of Grignard and Organolithium Reagents (R-M)to Nitriles... 

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