And electrofuges

Whereas the terms nucleophile and electrofile refer to bond-formation reactions, the terms "nucleofuge" and "electrofuge" refer to bond-cleavage processes (see footnote 3 of ref 2b). 

It should be pointed out that this reaction has been carried out photochemically (i.e., the photo-Nazarov cyclization Fi2) or under near-critical water conditions. More importantly, it has been improved to occur in a controllable fashion, through a directed Nazarov cyclization or an interrupted Nazarov reaction. It is worth noting that two practically directed Nazarov cyclizations have been developed, one by Denmark by using the jS-cation stabilizing effect and electrofuge of silicon (Scheme 2),2 > 2tt,6,i3 and the other from Ichikawa by application of a /3-cation destabilizing effect and the... 

The terms nucleophile, electrophile, nucleofuge, and electrofuge are typically used in discussing reactivity and kinetics. Hence, when one refers to a good nucleophile or electrophile, this means that the nucleophile or electrophile reacts faster than some reference nucleophile or electrophile. The same can be said for a good electrofuge or nucleofuge. 

The following list of reactions shows the most common uses of the various acronyms. Many more exist, but we only show the ones that you are likely to encounter while reading the literature. N and E represent generic nucleophiles and electrophiles, respectively, while N and E are nucleofuges and electrofuges, respectively. X is typically a halogen, while Y is a group that can support a radical. We also list the section where discussions of these mechanisms can be found. 

Allylic titanates having an electrofugal leaving group, e.g., trimethylsilyl68 75 - 77, at the 3-position are powerful reagents for the highly stereoselective synthesis of 1-hetero-substituted 3-alkadienes. For the carbonyl addition of the appropriate titanated allyl sulfides ( ) or carbamates ( and ), reliable y-selectivity and anti diastereoselectivity are reported. The... 

In addition to protons, other electrofugic leaving groups such as SO3 (i. e., anions of sulfonic acids), Cl, Br, I, C02, and others can also be displaced in azo coupling reactions with aromatic substrates. The mechanism of such substitutions is in principle the same as that of dehydrogenation (see Fischer and Zollinger, 1972). 

The Stiles-Sisti reaction (Scheme 12-17) is an azo coupling reaction in which an a-hydroxyalkyl residue is the electrofugic leaving group (Stiles and Sisti, 1960 Sisti et al., 1962). The reaction is used to prepare aldehydes and ketones (e. g., 2-methoxy-... 

Step 1, Second Symbol. A bond is being broken between C and H. The symbol is D. In any process, the subscript is E if a core atom is forming a bond to an electrophile (Ag) or breaking a bond to an electrofuge (De). Since C is a core atom, the symbol here is De- Alternatively, the symbol could be Dh- The rules allow Ah or Dh to replace Ae or De if the electrophile or electrofuge is H. Because a core atom is involved in this primitive change the H in the subscript is capitalized. 

Effect of Leaving Group. For both SeI and second-order mechanisms, the more polar the C—X bond, the easier it is for the electrofuge to cleave. For... 

Two new reactivity indices related to electrophilicity and nucleophilicity, electro-fugality and nucleofugality, have recently been introduced by Ayers et al. [59-61]. Electrofugality AEe is defined as... 

In fact, this heuristic principle (HP-8), which refers to nucleophilic heteroatoms directly attached to sp carbon atoms, may be also applied to nucleophilic heteroatoms directly attached to sp olefinic carbon atoms. In such cases, however, rather than a "disconnection" we would have an "unri-elimination" which will afford the substituted heteroatom as the "nucleofuge" and a triple bond as the "electrofuge". 

Electrofugal leaving of further hydrogen atoms linked at this carbon atom is promoted by insertion of the strongly electronegative fluoride ion and the formation of the C-F bond. Repetition of this mechanism leads to perfluorina-tion. In these molecules the reaction proceeds until there is complete substitution of hydrogen atoms. After this, the perfluorinated molecule leaves the adsorption layer at the anode and moves into the bath. 

In the vast majority of aromatic electrophilic substitutions, the leaving group is H (it is certainly one of the best), and very little work has been done on the relative electrofugal... 

In this method decarboxylation takes place by the arenium ion mechanism,440 with H+ as the electrophile and C02 as the leaving group.441 Evidently, the order of electrofugal ability... 

Electrophilic substitution allows replacement of a proton or another electrofuge with a different group and is the most-used process for functionalizing aromatic rings, whereas nucleophilic substitution is often considered to be more difficult or to require special substituents or reaction conditions. Prior to 1970, only two significant classes of nucleophilic substitution processes on aromatic rings had been... 

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