Carbon-centered nucleophiles organolithiums

As nucleophiles, these compounds react with the electrophilic carbon atom of the carbonyl groups of aldehydes and ketones (Chapter 16) and of carboxylic esters and acid chlorides (Chapter 18). Herein lies the value of organomagnesium and organolithium reagents in synthetic organic chemistry—as carbon-centered nudeo-philes, they enable the formation of new carbon-carbon bonds. 

Reaction with even harder nucleophiles such as organolithiums and Grignard reagents is substantially limited by virtue of the fact that these carbon nucleophiles add by direct attack at the metal center, as opposed to the softer carbon nucleophiles which add by attack on the allyl ligand. Direct metal addition can lead to the opening of alternative reaction pathways, e.g. 3-H elimination, in competition with reductive elimination which accomplishes nucleophile allylation (equation 40). 

The addition of Grignards and organolithium reagents proceeds by attack at the metal center in ir-allylpalladium complexes. The regiochemical selectivity exhibited by these hard carbon nucleophiles with ir-allyl complexes substituted at the termini with alkyl or aryl groups is comparable to the soft carbon nucleophiles (ligand attack) in most cases, with addition occurring predominantly at the less substituted terminus (equations 248 and 249).1591387... 

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