Nucleophiles conjugated with

The allylic esters 189 and 191 conjugated with cyclopropane undergo regio-selective reactions without opening the cyclopropane ring. The soft carbon nucleophiles are introduced at the terminal carbon to give 190, and phenylation with phenylzinc chloride takes place on the cyclopropane ring to form 192[120]. 

In agreement with these analyses, it was found that conqiound S was unreactive toward base-catalyzed cyclization to 6, even though the double bond would be expected to be reactive toward nucleophilic conjugate addition. On the other hand the acetylene 7 is readily cyclized to 8 ... 

In the absence of heteroatom containing substituents (e.g. halo-, cyano-), at or conjugated with the radical center, carbon-centered radicals have nucleophilic character. Thus, simple alkyl radicals generally show higher reactivity toward electron-deficient monomers (eg. acrylic monomers) than towards electron-rich monomers (e.g, VAc, S) - Table 3.6. 

Michael addition is a 1,4-addition reaction of a nucleophile to an a, /1-unsaturated system in which the double bond is conjugated with a carbonyl group, enabling the formation of the corresponding enolate as an intermediate (equation 27). 

In the first mechanism (equation 74) the nucleophile function attacks the aromatic ring in an ipso-type displacement involving a Meisenheimer complex intermediate243,244, and leads to the rearranged product after expulsion of sulfinate anion (X-). This mechanism should be favoured by the presence of an electron-withdrawing substituent in conjugation with the anion. The second mechanism (equation 75) involves a direct displacement of sulfinate anion (X ) by Y-, without involvement of the aromatic n electrons. 

Alcohol (34) is needed and we shall want to use a photocycloaddition to make some derivative of it (ether or ester). One partner in the cycloadd ition will be nucleophilic (CH2=CH0R) so we need a carbonyl group conjugated with the cyclohexene. FGA is required. 

The (3-carbon atom of an enamine is a nucleophilic site because of conjugation with the nitrogen atom. Protonation of enamines takes place at the (3-carbon, giving an iminium ion. 

In general these reactions are base-catalysed in that it is necessary to remove a proton from HCXYZ in order to generate the carbanion, eCXYZ, the effective nucleophile one or more of X, Y and Z are usually electron-withdrawing in order to stabilise it. The initial adduct (84) acquires a proton from the solvent (often H20 or ROH) to yield the simple addition product (85). Whether or not this undergoes subsequent dehydration (86) depends on the availability of an H atom, either on an a-carbon or where X, Y or Z = H, and also on whether the C=C so introduced would, or would not, be conjugated with other C=C or C=0 linkages in the product ... 

A 7r-bond can react with various active species, such as the electrophile oxene and its isoelec-tronic species (nitrenes and carbenes) and radicals. A 7r-bond can also react with a nucleophile, when it is conjugated with an electron-withdrawing group. In these reactions O, N, or C atom(s) are transferred from the active species to the olefins, forming two tr-bonds, such as C—O, C—N, and C—C, at the expense of the 7r-bond. If the 7r-bond is prochiral, chiral center(s) are... 

The formation of a phosphorimidazolide intermediate provides better reactivity toward amine nucleophiles than the EDC phosphodiester intermediate if EDC is used without added imidazole. The EDC phosphodiester intermediate also has a shorter half-life in aqueous conditions due to hydrolysis than the phosphorimidazolide. Although EDC alone will create nucleotide phosphoramidate conjugates with amine-containing molecules (Shabarova, 1988), the result of forming the secondary phosphorimidazolide-activated species is increased derivatiza-tion yield over carbodiimide-only reactions. 

There does not have to be a leaving group if the nucleophile reacts with a double bond however, in general, alkenes are not very reactive toward nucleophiles. An exception is if the double bond is polarized by conjugation with a carbonyl group. The reaction of... 

Some drugs such as penicillin have been shown to induce autoimmunity as well as anaphylaxis (Gleichman et al., 1989). The carbonyl of the /1-lactam ring of penicillin can form a covalent penicilloyl conjugate with nucleophilic sites on proteins, particularly the amino groups of lysine residues. This conjugate, which acts as the major immunogenic determinant, may become biotransformed to other isomeric forms of clinical relevance (Batchelor et al., 1965). 

---