Ambident, phenoxide

The Reimer-Tiemann reaction probably involves the attack of dichloro-carbene at the carbon of the ambident phenoxide ion. Conversely, only the oxy site of phenoxide ion intercepts the much harder difluorocarbene (13). Dibromocarbene attacks on the soft donor atom of thiophenoxide to give triphenylthiomethane (14) via further Sn2 displacement of the intermediate. 

Molecules having two reactive centers that are noninteracting or only weakly interacting, such as the carboxylate anions in malonate or succinate, are not considered to be ambident. The term bifunctional should be used to describe these compounds. If a molecule contains more than two interacting centers, the terms polydent or multident should be used. Examples of such nucleophiles include anions derived from malonic esters, /3-keto esters, /8-diketones, as well as phenoxide ions. 

This study reports on the reactions of ambident nucleophiles with electron-deficient nitroaromatic and heteroaromatic substrates anionic complex formation or nucleophilic substitution result. Ambident behavior is observed in the case of phenoxide ion (O versus C attack) and aniline (N versus C attack). O or N attack is generally kinetically preferred, but C attack gives rise to stable thermodynamic control. Normal electrophiles such as 1,3,5-trinitrobenzene or picryl chloride are contrasted with superelectrophiles such as 4,6-dinitrobenzofuroxan or 4,6-dinitro-2-(2,4,6-trinitrophenyl)benzotriazole 1-oxide (PiDNBT), which give rise to exceptionally stable a complexes. Further interesting information was derived from the presence in PiDNBT of two electrophilic centers (C-7 and C-l ) susceptible to attack by the ambident nucleophilic reagent. The superelectrophiles are found to exhibit lesser selectivity toward different nucleophilic centers of ambident nucleophiles compared with normal electrophiles. 

The first instance of the ambident reactivity of phenoxide ion toward nitroaromatics was reported from this laboratory. Thus, phenoxide ion reacted with TNB to yield the carbon-bonded adduct 7 (26) up to that time only the oxygen-bonded adduct 8 had been reported (27) ... 

Similarly, with phenoxide ions, oxygen attack is kineticaUy favored, while attack by the para- or ortho-ring carbons gives thermodynamically more stable adducts [130]. It is worth noting that earlier work was hampered by the competition with phenoxide of attack by hydroxide ions formed from small amounts of water in the solvent. Ambident attack by pyrrolide anions may involve reaction at nitrogen or carbon centers [132]. DMSO usually acts as an inert solvent for these measurements, but attack by its anion, the dimsyl ion, may involve successive reaction at oxygen, sulfur, and carbon centers [133]. 

The phenoxide ion has nucleophilic character both at the oxygen and at the carbon para to it it is ambident. 

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