Electron-deficient reagents

While die above reactions represent only a small fraction of die reactions known for palladium, they form the basis of a powerful methodology for building carbon structures. Several variations have been developed which utilize certain types of reactants and give particular types of products. All diese variations, however, contain a common theme. In each case an electron-deficient reagent (e.g., a vinyl halide or aromatic triflate) reacts with an election-rich reagent (e.g., an alkene, an organoborane, or an organotin) witii the formation of a new carbon-carbon bond. In that sense diese reactions are related to die reactions between carbon nucleophiles and carbon electrophiles discussed previously in diis chapter. They are quite different, however, because diey proceed only in the presence of Pd(0). In fact they proceed only in die coordination sphere of Pd(0). The ability of Pd(0) to catalyze diese reactions is nearly unique We will now examine some of die more common processes. 

As mentioned in Section I, one of the remarkable features of 1,1-enediamines is the enhanced enaminic reactivity of the / -carbon atom. 1,1-Enediamines can serve as nucleophiles in substitution of and addition reactions to a wide variety of electron-deficient reagents. In this section we discuss mainly the alkylation, arylation and acylation reactions of 1,1-enediamines, emphasizing their synthetic utilities, especially those of secondary enediamines. 

Just as different substituents are able to stabilise carbocations by releasing electrons towards them, substituents can release electrons into double bonds or draw them out from it. Electron donating groups such as alkyl groups and ethers will increase the electron density of double bonds to which they are attached. Therefore, in hydrocarbons the more heavily substituted double bonds will be more electron rich. So, if there are two or more double bonds in a molecule, electron deficient reagents such as ozone or peracids will preferentially attack the more/most electron rich olefin. 

The problem is particularly acute in the subject of addition reactions of alcohols, enols and phenols that is, there are two kinds of processes that might be imagined. First, there is the addition of the electron-deficient reagent to the electron-rich oxygen of the alcohol, enol, or phenol. Enols also undergo addition reactions with reagents that add to the carbon-carbon double bond. 

However, intermolecular C-F activation, as noted for some of the electron deficient reagents above, would be most important for catalytic or synthetic applications. 

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