Electrophilic C=X double bonds

Unlike the nucleophilic substitution reactions which generate stable onium halide after the reaction, nucleophilic additions to electrophilic C=X double bonds (X=C, N, O) provide rather basic onium anion species as an initial product. If the anion is sufficiently stable under the reaction conditions, onium anion will then exchange the counter ion for the other metal carbanion at the interface to regenerate the reactive onium carbanion Q+R. In another scenario, the basic onium anion may abstract the acidic hydrogen atom of the other substrate to provide Q 1 R directly. Such a reaction system ideally requires only a catalytic amount of the base although, in general, a substoichiometric or excess amount of the base is used to lead the reaction to completion. An additional feature of this system is the substantial possibility of a retro-process at the crucial asymmetric induction step, which might be problematic in some cases. 

One possible solution of this problem is to differentiate a radical first as electrophilic or nucleophilic with respect to its partner, depending upon its tendency to gain or lose electron. Then the relevant atomic Fukui function (/+ or / ) or softness f.v+ or s ) should be used. Using this approach, regiochemistry of radical addition to heteratom C=X double bond (aldehydes, nitrones, imines, etc.) and heteronuclear ring compounds (such as uracil, thymine, furan, pyridine, etc.) could be explained [34], A more rigorous approach will be to define the Fukui function for radical attack in such a way that it takes care of the inherent nature of a radical and thus differentiates one radical from the other. 

Addition of two electrophiles to an electron-poor C-C-double bond (C=C) or a C-heteroatom double bond (C=X) ... 

Lithium metal or alkyllithium derivatives react with dihalocyclopropanes to provide the corresponding lithiohalocyclopropanes I which are stable at temperatures around —100 °C. These metalated species are easily trapped with electrophiles (R—X) like methyl or ethyl iodide, trimethylstannyl chloride, tri-methylsilyl chloride etc. In the case of the unsaturated bicyclic substrate II a double bond migration is observed, which in the presence of excess starting bromide is accompanied by isomerization of the axo-lithio intermediate III to its endo-isomer IV [58],... 

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