Nucleophiles moderate

The reaction of chlorodifluorotnethane with alkoxide ions generated in low concentration from halide ions and epoxides [28, 29] is an interesting, higher temperature method that gives good to excellent yields of gem-difluorocyclo-propanes from just moderately nucleophilic olefins (equation 9)... 

The pyrolysis of sodium chlorodinuoroacetate is still a widely used, classical method for generating difluorocarbene, especially with enol and allyl acetates [48, 49, 50, 51] (equation 21) A convenient alternative that avoids the hygroscopic salt uses methyl chlorodifluoroacetate with 2 equivalents of a lithium chlonde-hexa-methylphosphoric triamide complex at 75-80 °C in triglyme [52], Yields are excellent with electron-rich olefins but are less satisfactory with moderately nucleophilic alkenes (4-5% yields for 2-bulenes)... 

It is now clear that acridizinium compounds and their benzo analogs are more susceptible to cycloaddition than are their quinolizinium counterparts. Fields et al. (68JOC390) showed that, even with the strong nucleophile 1,1-diethoxyethylene, 2,3-dimethylquinolizinium ion (35a) does not react. As yet the only quinolizinium derivative known to undergo cycloaddition is the anhydride (35b) of quinolizinium-2,3-dicarboxylic acid which, because of the increased electrophilicity provided by the electron-withdrawing substituents, undergoes cycloaddition even with the more moderately nucleophilic styrene to yield (36). 

Then we have the moderate nucleophiles. These are nucleophiles with a negative charge that is very stable. The halogens (F, Cl, Br, I) are excellent examples. When they have a negative charge, they are fairly stable. Other examples include resonance-stabilized ions, where the charge is spread out over more than one electronegative atom ... 

Answer We look at the substrate and we see that it is secondary. That doesn t tell us much, so we move on to the nucleophile and we see that it is a moderate nucleophile (not strong and not weak) that doesn t tell us much either. We then look at the LG and see that it is a good LG (not excellent and not bad), which that doesn t tell us anything either. Finally, we look at the solvent. This is a polar aprotic solvent, and that serves as the tie breaker. S>j2 wins. 

Coordination catalysts, which are usually applied for the polymerisation and copolymerisation of heterocyclic and heterounsaturated monomers, involve a wide range of metal derivatives characterised by a moderate nucleophilicity and relatively high Lewis acidity. Compounds of group 2 and 3 metals, such as zinc, cadmium and aluminium, as well as transition metals, such as iron, are representative coordination catalysts. The appropriate Lewis acidity of the metal and the appropriate nucleophilicity of the metal substituent in the catalyst make the monomer coordination favourable prior to the nucleophilic attack of the metal substituent on the monomer not yet coordinated. 

When we wish to make (3-lactams by the alternative addition of an isocyanate to an alkene, a substituent on nitrogen is again required, but for quite a different reason. Because alkenes are only moderately nucleophilic, we need a strongly electron-withdrawing group on the isocyanate that can be removed after the cycloaddition, and the most popular by far is the chlorosulfonyl group. The main reason for its popularity is the commercial availability of chlorosulfonyl isocyanate. It reacts even with simple alkenes. 

The 3jS-chloro compound (8) reacts by the Sh2 mechanism with moderately nucleophilic species, including acetate ion and benzylamine, to give mainly 3a-substituted products. The weaker base aniline failed to react in this way, giving the 3/S-anilino derivative. 

If, on one hand, isosafrole is considered a moderately nucleophilic alkene, owing to the injection of electron density into the styrene structure by the oxygen substituent, the three electrophilic centers of compound I (denoted by asterisks) ostensibly do not participate as bonding centers in this reaction. The electrophilic or receptor role is somehow assumed in turn by the potentially... 

Chloride ion generally is a moderate nucleophile and a weak base. However, in the following dehydrohalogenation reaction, chloride ion functions as a base, removing a proton to bring about elimination of the elements of HCl. 

Thioacyl chlorides, RCSCl, are powerful thioacylating agents as is obvious from the quantitative thiobenzoylation of the only moderately nucleophilic nitrogen in thiocarbamate (13 equation 5). However, severe limitations are the difficult accessibility of thioacyl chlorides and their thermal lability. Even if they are prepared from dithiocarboxylic acids using an improved procedure, only thioaroyl chlorides, particularly PhCSCl (12), can be handled sufficiently easily to be used in synthetic work. Thus, various azoles react with (12) to furnish /V-thiobenzoyl azolides (14) in the presence of excess azole or NEts (equation 6) a particularly clean and fast reaction is achieved if IV-silylated azoles are employed. However, considering the fact that the chloride has to be prepared from the dithiocarboxylic acid, the approach of equation (4) presents a shortcut to the products. 

Compared with alcohols, which possess a high standard potential of oxidation, moderate nucleophilicity and weak basicity, amines very often serve as good electron donors and relatively strong bases and nucleophiles in chemical reactions. Photoinduced electron transfer (PET) processes, in which an amine donates an electron to the reaction partner in either its ground or excited electronic state, result in the formation of an amine substrate exciplex (Scheme 6.196).670 1224 The driving force for electron transfer is related to the standard potential of oxidation of the donor, the standard potential of reduction of the acceptor and the excited state energy of the absorbing partner (see Chapter 4). 

Diazoketone decomposition. Cyclopropanation of a proximal electron-rich double bond, for example, of an indole nucleus, is inescapable once carbenoid generation is initiated. By placing a moderately nucleophilic chain that is stericaUy interactable with the emerging cyclopropane, skeletal reorganization is feasible. Such transformation based on careful design is conducive to synthetic purposes. ... 

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