Electrofugal

Compounds 1, which bear in X an electrofugical leaving group, such as trialkylsilyl or diphenylphosphinyl, are of high value for the synthesis of stereochemically homogeneous 1,3-dienes via stereospecific anti or urn elimination. 

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... 

The replacement of an electrofugic atom or group at a nucleophilic carbon atom by a diazonium ion is called an azo coupling reaction. By far the most important type of such reactions is that with aromatic coupling components, which was discovered by Griess in 1861 (see Sec. 1.1). It is a typical electrophilic aromatic substitution, called an arylazo-de-hydrogenation in the systematic IUPAC nomenclature (IUPAC 1989c, see Sec. 1.2). 

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-... 

Replacement of electrofugic leaving groups other than protons is called //750-substitution. For a discussion of o-complexes see Sec. 12.8. 

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. 

Unlike alkylation, Friedel-Crafts acylation has been generally considered to be irreversible, but a number of instances of electrofugal acyl groups have been reported, especially where there are two ortho substituents, for example the hydro-de-benzoylation of 42. ... 

CO2 as the leaving group. Evidently, the order of electrofugal ability is CO2 > H + > COOH, so that it is necessary, at least in most cases, for the COOH to lose a proton before it can cleave. 

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". 

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). 

To summarize, by modifying in -C-O- either the leaving group abilities of the carbon moiety (the electrofuge) (e.g., by alkyl substitution at or by ionization of OH) or those of the nitrobenzene (by substitution at the ring) it is possible to go all the way from pure addition to what appears to be pure electron transfer. The heterolysis rates increase with increasing electron push ... 

A leaving group that departs with the bonding electron pair. The tendency of such a moiety to leave is referred to as nucleofugicity. See also Electrofuge Nucleophile... 

BASE STACKING NUCLEOFUGE ELECTROFUGE NUCLEOPHILE NUGLEOPHILE... 

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